Preliminary Draft $Id: wavetrain.html,v 3.3 2000/02/15 22:35:08 douzzer Exp douzzer $ Author: Daniel Pouzzner email: <email@example.com> Copying: This paper, including this header, may be redistributed freely provided it is unaltered and unabbreviated. The author retains any and all copyrights.
Please note (2001-Apr-25): this paper is currently under massive revision. The material in this version is for the most part fundamentally correct, if wrong on various important physiological and dynamical details, but the dearth of detail and support is overwhelming. The version in preparation rectifies largely these faults. Browse some prospective references.
preview of upcoming revision, 2001-Aug-19:
The mammalian cerebral cortex and thalamus are interconnected by an exhaustive array of excitory projections that support self-sustaining reverberation associated with the sensory, cognitive, emotive, and motor domains. This reverberation exhibits a dynamic that is chaotic to a degree dependent on the instantaneous conditions of the reverberation and of the myriad projections that influence and drive it. The chaotic dynamic of the corticothalamic reverberation, as guided by the striatal complex, constitutes a default mode of goal pursuit that emerges in the absence of focused and directed goal pursuit. The chaotic meander through corticothalamic phase space tends to identify specific, often novel strategies of goal pursuit. The chaotic meander collapses in a spontaneous and coordinated fashion into the strategy of focused and directed goal pursuit that precipitated from the meander. When goal pursuit by the identified strategy is exhausted, the chaotic meander resumes. Complex goals consist of subgoals, and a chaotic meander due to exhaustion of a strategy for pursuit of a subgoal is typically constrained by unexhausted pursuit strategy for higher goals.
Corticocortical projections, and nonreciprocal pathways from cortex through the thalamic association nuclei and the claustrum and back to cortex, interrelate otherwise segregated reverberative channels, adding degrees of freedom. The pallidum and SNr differentially modulate the gain of this reverberatory system, effecting a sequence of transient attractors. When the input stage of the striatal complex is strongly and focally excited, this leads to a deep focal inhibition of the pallidum/SNr, focally facilitating corticothalamic excitation (multiple foci can coexist at each stage). Pallidal inhibition leads to subthalamic disinhibition, which enhances the inhibitory output of the pallidum/SNr outside the focal disinhibition. This eliminates or greatly attenuates the chaotic dynamic of the corticothalamic reverberation.
Prefrontal cortex is a zone of convergence for projections from all (or very nearly all) sensory, cognitive, and motor modalities represented in cortex. The incoming signals are combined, and some patterns trigger a signal to VTA (corresponding to either reinforcement or deterrence). A goal is, in short, the association of one of these prefrontopetal patterns of activation with a level of reinforcement or deterrence. Prefrontal cortex is distinguished in that it, alone among neocortical regions, is innervated by VTA. Goals are first formed in PFC in response to reinforcement and deterrence generated by the amygdala and hypothalamus (embodying phylogenetic goals) through their projections to VTA. Subsequently, goals also form in PFC in sympathetic response to the action of existing PFC goals. Phylogenetic and PFC goals can also dismantle another PFC goal, by generating deterrence coincident with the activation of the other goal. PFC reciprocates with the widely distributed regions that innervate it, and projects to the input stage of the striatal complex, and to the subthalamic nucleus. When a pattern of excitation initiated by PFC to those regions is followed by reinforcement, the pathways that generated that pattern are strengthened so that they are more easily excited, and the pattern is more likely to recur. In a fashion analogous to PFC, the amygdala and hypothalamus send signals to cortex, thalamus, and the striatal complex, that tend to directly precipitate amygdalar and hypothalamic goal pursuit behavior. These signals are of necessity far less precise and versatile than those with prefrontal origin: indeed, the basal forebrain emotive centers are reliant on the modeling and executive acumen of the prefrontal cortex for effective pursuit of phylogenetic goals.
Through corticostriatal and striatopallidal divergence and convergence (including ventral and nigral pathways), information (sensory, cognitive, motivational, motor) represented in cortical state (and the corticothalamic reverberation) is associated with itself in a grand variety of combinations at the input stage of the striatal complex. This combinational corticostriatal synaptic interface is sculpted (through reinforcement/deterrence coordinated via SNc, VTA, PPT, LDT, Meynert, and other loci) so that it transforms input patterns into output patterns that tend to lead to reinforcement. The output of the striatal complex, driven largely by PFC, disambiguates the direct output of the PFC to other cortical regions.
The claustrum and cortex constitute a reverberatory system akin to that of the thalamus and cortex, but without a counterpart to the reticular nucleus (nRt) of the epithalamus (which inhibits unrestrained synchronous corticothalamic oscillation) and without differential damping by the pallidum and SNr. A chaotic dynamic may be prominent in this subsystem, but it is well established that the claustrum is a sensitive site for kindling of seizures, suggesting that the absence of an nRt-like regulator facilitates global synchronized oscillations that are not particularly chaotic. The anterior nuclei are also unregulated by nRt and the striatal complex, and the hippocampal region - with which the anterior group is intimate - is the brain's most sensitive site for kindling. Since the hippocampal region participates intimately in the corticothalamic reverberatory dynamic, the corticoclaustral reverberation probably does too, probably in a similarly distinguished capacity.
In this summary I have neglected various important organizational and dynamical schemes, among which are (1) the topical scheme in cortex, striatum, and thalamus, (2) the functional implications of the separable organs, pathways, and compartments, of the striatal complex - particularly, the intimacy of the ventral complex with VTA and the dorsal complex with SNc, (3) the effects of intralaminar thalamic innervation of the neostriatum, and the functional implications of the thalamic nuclear divisions in general, (4) the automatic recapitulation of rote condition-response associations by the cerebellum, (5) phylogenetic motivation and goal centers other than the amygdala and hypothalamus, and relay pathways for signals from these emotive centers, and (6) a large set of nuclei that integrally and inseparably support and affect the operation of the anatomy mentioned herein, particularly those in the pons and midbrain. I will address all of these in detail in the final product.
Most of isocortex is segmented into maps that are quasicontinuous topographical representations of qualia spaces. Isocortical maps are in two dimensions. The array of maps is phylogenetically predetermined, in rough form, by cytoarchitectural and myeloarchitectural distinctions, particularly regarding connectivity with the thalamus. The least associative such representations are in distorted but regular spatial registration with sensory and motor organs. The most associative such representations relate a class of complex geometric, temporal, or logical (i.e. topological, symbolic, abstract) relation to a topographic field consisting of a representive and graded range of the members of the class. Nearby maps are often closely related in their meaning, and such maps are often in partial or complete topographic registration with each other. These maps are plastic, and adapt to the pattern of usage, expanding representations of frequently encountered qualia (enhancing resolution in its vicinity, thereby more closely approximating a truly continuous representation for frequently encountered qualia), and shrinking representations of seldom encountered qualia. Prefrontal cortex includes regions that are transiently mapped from moment to moment, providing utmost versatility and associativity.
The thalamus is segmented into nuclei most of which are associated with a particular usually contiguous set of one or more isocortical maps, so that most of the thalamus is, like isocortex, segmented into maps that are quasicontinuous topographical representations of qualia spaces. Thalamic maps are in three dimensions. Many thalamic nuclei receive topographically organized signals via the brain stem and optic tract from sensory organs, and these nuclei impose a phylogenetically predetermined map on the isocortical maps with which they are intimate. Nearly any particular locus in the thalamus is part of a map that is related in a regular topographic fashion to some isocortical map with which it is physiologically intimate. Associative thalamic nuclei have additional relationships with isocortical maps with which they do not share a regular topographic relationship. A thalamic map adapts plasticly in conjunction with adaptation in the cortical maps with which it is intimate. The mediodorsal nucleus is the thalamic counterpart of the transient frontal cortical maps.
Corticothalamic reverberations (and, in a more specialized role, corticoclaustral reverberations) are short term working memory, engendering mental continuity on the scale of seconds by simultaneously representing recent mental history on that time scale. A momentary state of consciousness is equal to the contents of this reverberative system at that moment. This mechanism makes no direct use of neural plasticity in representing mental history, though over longer periods plasticity will lead to adaptation for patterns of usage.
Corticocortical and non-reverberative corticothalamocortical and corticoclaustrocortical pathways cause automatic, rapid self-association of the mental world-state according to a phylogenetic blueprint of adaptive associations. These structures engender mental continuity on an inter-generational time scale of millenia. Corticothalamocortical and corticoclaustrocortical association pathways have timing that matches that of corticothalamic reverberations, so that propagative spatiotemporal registration between reverberations and associations is maintained. Pathways through the thalamus bring the cortex under the influence of several major modulatory systems, among them the striatal complex, the cerebellum, and the thalamic reticular nucleus. These modulatory systems sculpt and tune the corticothalamic dynamic (hence, awareness, attention, and action).
Long term declarative/episodic memories are a form of self-association embodied in corticocortical relationships, existing within and enriching phylogenetic corticocortical relationships, engendering mental continuity for the lifetime of the individual. Mental states that share features of a memory tend to stimulate the recall of that memory. The probability of recall increases as the number of shared features increases.
The striatal complex selects and directs focused attention and action, computing and directing plans for efficient transit from current cognitive and motor state to the target state represented or identified within the current state. It is informed by isocortex, thalamus, and the hippocampal region, and causes effects by focally disinhibiting the thalamus (whence the signal returns to cortex). It has a rough phylogenetic configuration, with an array of plastic maps akin to those of the cortex and thalamus. Striatal maps are three dimensional. The cortical input is distributed in a highly associative manner, relating each cortical map with several striatal maps, each striatal map with several cortical maps, and certain intensely associative cortical maps with great arrays of striatal maps. There is nonetheless a substantial degree of domain segregation, particularly in the stages following the neostriatum. The whole complex is arranged for rapid reinforcement-based learning, by which it develops expertise in relating particular cortical input patterns to effects (attention and action) that lead to reward. The expertise of the striatal complex engenders logical continuity of mental states for the lifetime of the individual. Its output returns via the thalamus to key regions of isocortex, completing a closed circulatory system whereby trains of directed thought (streams of consciousness) are conducted. These key regions contain the same intensely associative cortical maps that have extraordinarily broad projections to the striatum, and are the cortical centers of command and planning.
The hippocampal region engenders mental continuity on time scales longer than the few seconds bound together by short term working memory, by simultaneously representing selected portions of mental history from the preceding two weeks. This mechanism is based on the intense plasticity of the hippocampal region. The pathways from cortex and thalamus to the hippocampal region supply the latter with a mental world-state, and the pathways from the hippocampal region to isocortex allow recreation of that mental world-state. The hippocampal region acts as an intermediate-term memory, standing in for memories until they are consolidated in isocortex. During sleep, hippocampal memories revive while isocortex is in a state of heightened plasticity, causing their consolidation in isocortex as long term memories. Each memory initially has a set of handles - loci the stimulation of which revives all the cortically disparate components of the memory - which the hippocampal region initially simulates. The consolidation process is the selective construction of these handles in isocortex at successively greater geometric and topological distance from the hippocampi and dentate gyri proper, until finally the interconnections between the memory components are so established that no distinguished handle is needed. However, recall of the memory causes the consolidation process to begin again, starting with a parahippocampal representation.
The cerebellum stores and reproduces simple, well-defined habits akin to programmable reflexes. These habits are stereotyped transformations of current attentive, intentional, or motor state into an immediately subsequent such state. Moreover, by chaining transformations together, the cerebellum effectively stores short sequences (and even cycles) of such states. Domains of state (most broadly, the externally directed motor and internally directed cognitive domains) are largely segregated and unassociated in the cerebellum. State transformation by the cerebellum is very rapid, and after a lengthy process of learning supervised by the cortico-striato-thalamic system, is very precise. Indeed, because of its anatomical position (its peduncles attach directly to the brain stem), it is able to coordinate action with an agility the forebrain cannot match. Thus, the cerebellum can learn actions that the forebrain evaluates and corrects, but cannot itself perform. The cerebellum receives a diverse, though not exhaustive, array of sensory, cognitive, and motor signals. The cerebellum generates cognitive and motor activity through a variety of output pathways, some of which return through relays to the areas from which cerebellar inputs are derived. The cerebellum attempts to associate each input pattern with a habit cue (initial state) in its store of habits. If a sufficiently similar cue is identified, the cerebellum generates output that reproduces the attentive, intentional, or motor habit (subsequent state). These automatic signals can be intentionally inhibited by action of the cortico-striato-thalamic complex. Cerebellar, striatal, and neocortical output signals converge in the thalamus, and the striatal signal may impose a mask that inhibits cerebellar signals outside the scope of the current context, to a degree proportional to the intensity of striatal activity.
The thalamus, cerebral cortex, and striatal complex, and more selectively, the cerebellum, are modulated for excitement, inhibition, reinforcement, aversion, and sleep coordination by chemically specific diffuse ascending modulatory systems emanating from portions of the pons and midbrain, hypothalamus, and basal forebrain, which are influenced to widely varying degrees (from subtle and slow to preeminent and rapid) by descending pathways.
Most of the structures implicated above are innervated by emotive structures within and neighboring the basal forebrain, most notably the amygdala and hypothalamus, which impose a wide variety of phylogenetic and learned actions, responses, and biases, triggered principally by signals from isocortex, allocortex, and thalamus. These impositions are a phylogenetic companion to the phylogenetic pathways of cortical association, operating on a similar timescale.
This paper presents and supports the thesis that consciousness is a fundamentally motive phenomenon which serves to integrate and coordinate activity throughout the neuraxis at the broadest level, and that this systemic coordination is achieved through circulation of a wavetrain through a circuit which encompasses diencephalic and telencephalic structures. This neural wavetrain is the essence of consciousness, and innumerable other wavetrains are the essence of the subconscious. The transformation and interaction of these wavetrains comprise the tapestry of mind. Throughout, I specifically and directly address issues of neurophysiology, psychology, and complex systems behavior.
2. Summary proposal
3. Myeloarchitectural hypotheses
3.1 The myeloarchitecture of consciousness
3.1.1 Conscious Circuits
3.1.2 Unconscious Motor Performance
3.2 On Hemispheric Symmetry and Asymmetry
3.3 The Memory Coordination Circuit
3.3.2 Memory and Isocortex
3.3.3 Recruitment and Binding of Symbolic and Spatial Context
3.3.4 Elaborations on the Mechanisms of Subconscious Information Management
3.4 Emotional circuits
3.4.1 The LeDoux Circuit
3.4.2 The Papez Circuit
3.4.3 The Amygdala: Primitive Directed Emotions
3.4.4 The Hypothalamus: Metabolic Drive
3.4.5 Pleasure and Pain
3.4.6 Excitement, Surprise, and Relief|
3.4.7 Corticostriatal Emotions: Success and Failure
18.104.22.168 Goal Structure
22.214.171.124 Falling in Love
126.96.36.199 Hate, Shame, Embarrassment, Contentment, and Joy
3.5 Thalamic Organization
3.5.1 Gross Anatomy
3.5.2 Reticular Nucleus as Attentional Spotlight
4. Speculation on the generic nature of circuits
4.1 Circuit dynamics
4.2 Circuit variety
4.3 The physiological mechanism of amalgamation
5. Future directions
7. Acknowledgements and Inspirations
Appendix 1 - Glossary
The theory I propose below is an attempt to account for the subjective and objective aspects of consciousness, at the level of physiology, drawing directly on the evidence uncovered by physiological research. Implicit in this accounting is a definition of consciousness, and a total theory of mind-brain.
Mammalian consciousness is the top-level integrative subjective point of view of a mammal. This point of view has three aspects: awareness, contemplation (conscious introspective cognition), and action. These are aspects of the unified phenomenon that is consciousness, and are not separable components. Note particularly the first and last aspects: awareness has a point of view, but action also does - actions are taken from a position, from a point of view. Conscious action is taken from the position of consciousness. And conscious contemplation is nothing less than the stream of consciousness itself, constituting a train of fleeting cognitive models. Consciousness is the preeminent engine by which sensation, memories, and the products of non-conscious cognition, are integrated with goal structure to drive action. Action is both internally directed (changing or creating memories, goals, and various components of internal state) and externally directed (precipitating signals to voluntary musculature to effect action).
The neurophysiological correlate of consciousness (NCC) identified herein is almost entirely confined to areas that are traditionally considered motor: frontal cortex, corpus striatum, and ventral anterior and rostral intralaminar thalamus. It is misleading to categorize them as motor organs, since they straddle the sensory-motor boundary. The mediodorsal thalamic nucleus, which is also implicated directly, is widely acknowledged to be grand integrative (straddling the sensory-motor boundary), and of course the whole of sensory cortex feeds into consciousness through intracortical, corticostriatal, and corticothalamic projections.
In my theory, consciousness is an operator - a function that has as input and output, functions. More than simply an operator, consciousness is an endless evolving train of operators. Mind and brain are seen to be two distinct components of a single unified phenomenon, mind-brain. Mind is the dynamically evolving transient state of the brain, and brain is the dynamically evolving persistent physiological structure through which mind courses. This is not in and of itself particularly controversial.
It is my fundamental hypothesis that consciousness is a circulating multidimensional wavetrain. A brain is a medium in which wavetrains, consciousness being the foremost such wavetrain, cyclically propagate, are transformed, and transform, initiate, and combine with other wavetrains, all of which entrain and are subjected to non-cyclic emotive and tonic influences. At several granularities and timescales, through a variety of mechanisms, the medium (consisting of myeloarchitecture, synaptic transfer functions, cell body transfer functions, and secondary effects thereof) alters the wavetrain, and the wavetrain alters the medium.
There is no anatomically localized seat of consciousness, but rather, a distinct but highly distributed one. The convolutional system of the neocortex and neostriatum, which will be described in detail below, constitutes the anatomical linchpin, but is not the seat of consciousness. One might maintain that the neostriatum is the seat of consciousness, because it is there that the vital convolutional function is dynamically constructed, but this is insupportable. The instantaneous convolutional function computed by the neostriatum is itself a function of the signal delivered to it by the neocortex, and the convolved output of the neostriatum makes its way back to the neocortex via the paleostriatum and thalamus, completing a circulatory pathway. The seat of consciousness is not an anatomical entity, but rather a dynamical one. It is the signal coursing through a circuit that includes these loci. The anatomical loci and projections that shuttle the signal around are not consciousness, but rather the signal itself is it.
The innumerable subconscious processes of the mind, processes which at opportune moments enter consciousness, are wavetrains circulating and evolving along physically disjoint (though closely and repeatedly interlaced) pathways. The means by which such a subconscious wavetrain is made to enter consciousness is by a breaking down of the barrier between the physical substrate of the appropriate subconscious wavetrain, and that of consciousness. In an interruption (an asynchronous realization, a reminder, the deferred recall of a memory, etc.) the state of the subconscious wavetrain is such that the physical substrate is modified to amalgamate the heretofore subconscious wavetrain with the conscious wavetrain. In an intentioned (single-threaded, willed, I-want-this) access or incorporation, the state of the conscious wavetrain catalyzes the topological modification. The substrate of the conscious wavetrain is such that it is extremely agile, able to assume states that precipitate nearly arbitrary simultaneous amalgamations with peripheral circuits of nearly arbitrary variety and size. Consciousness is not, however, at all able to assume arbitrary states in the more general sense. In particular, the modulations associated with the emotions cannot be directly stimulated or inhibited. Instead, their stimulation or inhibition must be precipitated indirectly through complex internal and external behavior, behavior which nonetheless can in many cases be refined to achieve a high degree of agility.
The myriad disjoint wavetrains of the subconscious join among themselves to form larger, semantically richer wavetrains. Eventually this amalgam of subconscious wavetrains may reach a level of richness and coherency which crosses a threshhold and causes incorporation of the wavetrain into the consciousness wavetrain. Alternatively, the amalgam may reach a dead end and simply decay.
Subconscious wavetrains routinely eavesdrop on the conscious wavetrain, without disturbing it, in order to enrich themselves and increase their relevance. The noise inherent in the neural substrate also serves to seed subconscious wavetrains, introducing completely new information permitting invention. It seems likely that many critical path circuits (chiefly, those pathways with regular mappings to sensory or motor fields) use extensive forward error correction strategies to conceal the inherent noise. The point here is that the brain's circuits are divided into two categories: those that deliberately damp out chaotic effects, and those that rely on them. It is expected that hard and discrete, i.e. phylogenetic, circuits fall into the former category, and that the vast array of soft circuits are formed and dissolved by a process which leverages off the attractor effects of nonlinearity cultivated in an architecture founded on the unifying principle of circulating wavetrains. Complicating this picture are arrangements in which soft circuits are components of hard circuits. The conscious circuit (and memory coordination circuit, discussed below) are special in that they are both distinctly phylogenetic and have a distinct chaotic component to their dynamics.
An example product of the subconscious amalgamation mechanism is the flash of insight, in which (at an opportune stage) consciousness is interrupted and presented with a cognitive model of some set of phenomena. Once this model becomes conscious, intentions (goals) based on that model can be readily formed through delineation and extension of existing intent. Hence, the amalgamation process is critical to creativity. Eavesdrop-based and noise-based seeding both play crucial roles in this scenario.
A recurrent and common mode of operation is for the conscious wavetrain to amalgamate with particular peripheral circuits, discover that the desired information is unavailable, and dissociate from those circuits having left them in a state which will evolve in such a way that they will seek the desired information and interrupt consciousness when it becomes available.
The various interruptions of consciousness by subconscious processes described above often occur particularly when consciousness has returned to a state in some way related to the subconscious process, biasing the associated conjunctive loci toward amalgamation. For example, a word lost one day is often spontaneously presented to consciousness, out of apparent context, days or even weeks later when another missing word is being laboriously sought in conversation. The commonality here is simply the unaccountable inability to recall a familiar word in conversation, causing recruitment of the same hardware to the task of tracking down a missing word through oblique indices, a commonality which is sufficient to precipitate interruption of consciousness by the subconscious word-search process.
Separable circuits dissociate when the portions of the wavetrain conveyed by each circuit become incoherent relative to each other, presumably manifested by a breakdown of temporal (including harmonic) and/or spatial registration between the wavetrains. A dominant component of the wavetrain, such as that of the core circuit of consciousness, is usually able to deliberately desynchronize and spin off wavetrains associated with amalgamated (but dissociable) circuits, reinstating their physical disjointness. Sometimes such an amalgamated circuit carries a wavetrain that is particularly pesky, and wages a battle of wills with the conscious wavetrain. More often, these internal battles are with organs that are operating by a non-circulatory mechanism (more on this below in section 3.4).
Several circuits are overlaid to construct the circuit that is necessary and sufficient for consciousness. Consciousness is a predictive, reactive, and motive phenomenon, and the organismic substrate is confined to regions traditionally considered to be associative motor. These regions are considered among the most poorly understood in the brain.
These circuits are not actually separate or in any way disjoint. Intranuclear and intraorganic linkages bind them together at all times. Dissociation or interruption of any of these circuits results in morbidity or catatonia. In functioning humans, this is a single highly complex circuit, tightly integrated in some manner which is not at all well understood. Consciousness is the wavetrain which courses through this complex. The corticostriatal and thalamocortical components of the circuit are likely dominant, with the other circuits acting in supportive roles, in some cases probably not constituting circulatory subsystems proper.
The caudate nucleus and putamen, constituting the neostriatum, are really a single continuous nucleus. Its organization is remarkable. From Carpenter: "Virtually all regions of the neocortex project fibers to the striatum and all parts of the striatum receive fibers from the cortex. No part of the striatum is under the sole influence of one neocortex area. Degeneration studies suggested that different regions of cortex projected to specific parts of the striatum with degrees of overlap. Autoradiographic studies revealed that (1) corticostriatal terminals form mosaic-like patterns in the striatum, (2) many cortical areas have widespread projections in several parts of the striatum, and (3) widely separated cortical areas give rise to overlapping terminal fields. The terminal distribution of corticostriatal fibers is extensive and characterized by a mosaic pattern of patches or clusters. The patches of striatal terminals arising from different cortical areas not only overlap each other but also may overlap terminal projection zones of other striatal afferents."
This arrangement is convolutional. The caudate nucleus in particular is likely vital to consciousness, as it receives projections from the prefrontal cortex throughout its extent. The topology of the corticostriatal system permits any signal anywhere in the neocortex or neostriatum to be routed anywhere within the conscious system, often in a single circulation. This likely constitutes in large part the neurophysiological correlate of the agility of consciousness described in section 2. Like the neocortex, the neostriatum represents the full spectrum of specificity, from somatotopically mapped fields to regions of associativity akin to that of granular frontal cortex.
The mediodorsal nucleus is probably the preeminent thalamic site at which amygdalar emotion is integrated into consciousness. In addition to its linkage to intralaminar nuclei and frontal cortex, the mediodorsal nucleus connects with the lateral nuclear group (implicated in memory coordination), the amygdala (seat of primitive directed emotions), and temporal cortex (containing handles for long term memory constellations). The connectivity of the mediodorsal nucleus indicates its significance to consciousness. The mediodorsal nucleus is particularly well-developed in humans, as one expects in an organism with far more complex social emotions and far more highly refined and relatively powerful consciousness.
The paracentral and central lateral nuclei are innervated by the brain stem reticular formation, an unsurprising relationship for nuclei implicated directly in consciousness.
Regarding the ventral anterior nucleus, from Carpenter: "Physiological data indicates that the ventral anterior nucleus may be functionally related to the intralaminar nuclei of the thalamus, in that recruiting responses in widespread cortical areas can be evoked by repeated low frequency stimulation of the nucleus. The recruiting response is a surface negative response evoked by repetitive low frequency stimulation of the ventral anterior, the midline or the intralaminar thalamic nuclei that waxes and wanes and can be recorded over broad areas of the cerebral cortex. The ventral anterior nucleus appears to be the preeminent site among thalamic nuclei for the production of the recruiting response."
Also from Carpenter: "The intralaminar thalamic nuclei show a striking development in primates and man, in relation to thalamic relay nuclei, suggesting that they constitute a complex intrathalamic regulating mechanism concerned with diverse functions. The intralaminar thalamic nuclei have been considered to serve as the thalamic pacemaker controlling electrocortical activities." This organization leads one to conclude that the intralaminar nuclei and the magnocellular portion of the ventral anterior nucleus (VAmc) are configured to pace, or clock, consciousness, and that the brainstem reticular formation - which is crucial in sleep coordination - is positioned to drive this clocking.
The paralaminar portion of the mediodorsal nucleus is richly and reciprocally interconnected with the frontal eye field, which is mostly within Brodmann area 8 (included in the frontal region implicated in the conscious circuit). This relationship probably serves at least partly to transduce amygdalar reactions into modulations of direction of gaze.
VAmc is also reciprocally interconnected with the frontal eye field, and this relationship is probably used principally for dispassionate deliberate directing of gaze. The frontal eye field is believed to be the preeminent site at which voluntary movement of the eye is directed, as distinguished from the stimulus-reactive saccades initiated by the superior colliculus and visual cortex. This intimacy of conscious thalamic nuclei with the saccade command center is quite natural.
A central role of the globus pallidus, older than the putamen and caudate nucleus (in fact, present in reptiles), and the most medial and central of the basal ganglia, is to serve as the last stop in the train of motor performance command before the train enters nuclei and cortical regions that are topographically mapped directly to voluntary musculature - that is, outbound trains. The centromedian and parafascicular nuclei - intralaminar nuclei not implicated directly in consciousness - are probably implicated in transducing intention into outbound motor stream, in conjunction particularly with the globus pallidus, receiving signals from precentral and premotor cortex and projecting to so-called non-limbic portions of the caudate nucleus and putamen. The parvicellular portion of the ventral anterior nucleus (VApc) receives projections from the medial pallidal segment and projects to supplementary motor cortex, indicating that VA is a likely site of transduction from internally directed (conscious) to externally directed (non-circulational) motive stream.
The globus pallidus transforms input from the neostriatum into output sent not only to the ventral anterior nucleus (largely constituting conscious motive stream), but also to non-associative (ventral-tier) direct-mapped thalamic motor relay nuclei (whence the signals reach primary motor cortex, the cerebellum, and in due course GSE and SVE nerves). Collaterals of these projections enter the centromedian nucleus of the thalamus, as mentioned above, creating a circulation from CM to neostriatum to pallidum and back to CM. I propose that the purpose of this circulation is to provide a feedback loop for adjustment and refinement of the command stream reducing the difference between the desired and actualized effect of initiated actions. This is particularly plausible since the neostriatum and globus pallidus have conscious roles, and the CM - like most, or all, intralaminar and midline nuclei - is linked to MD. However, the general mechanism for this adjustment is a system by which the substantia nigra compares signals from the neostriatum and globus pallidus, and provides reinforcement concomitant with the correspondence. The globus pallidus reciprocates with the subthalamic nucleus, and uses this system as an action buffer, probably facilitating effective use of the nigral reinforcement signal.
In addition to its role in transducing conscious intent into explicit motor acts, the globus pallidus is almost unequivocally the organ responsible for unconscious motor scripting - for relatively inflexible and stereotyped motor performance by rote without conscious orchestration. The GP issues sequences of commands, which may be looped, and which are refined, as are fully conscious commands with a corticostriatal origin, by the cerebellum. Likewise, the cerebellum is almost unequivocally the organ responsible for the unconscious storage and execution of stereotyped gestures of which pallidal scripts consist - though these gestures are stored as reactive filters (implicit memories) rather than the declarative (if subconscious) script memories of the GP.
It is striking that the human cerebellum is substantially larger than the primate cerebellum, relative to the rest of the brain. This is indicative of a further reassignment to the cerebellum of responsibility for coordination and gesture refinement functions, permitting a greater proportion of the corpus striatum to concern itself with associative functionalities of intentionality, and therefore, refinement of consciousness. The refinement of the command stream from the GP is less critical, so a richer repertoire of scripts can be stored, thereby relegating a higher proportion of activities to the category dispatched unconsciously, thereby requiring less neostriatal involvement (and therefore conscious involvement) in externally-directed, stereotypable activities. There are secrets yet to be unlocked in the cerebellum, though, and it is conceivable that among them is a "lint picker" functionality, in which the cerebellum (perhaps in concert with the GP) refines the dynamical evolution of entirely internal thought processes circulating in the limbic neostriatum and in frontal cortex rostral to area 6. That conscious sensations of pain and pleasure can be evoked through stimulation of cerebellar loci also hints at secrets yet to be unlocked. However, the significance of the cerebellum to cognition and emotion cannot be great, since massive bilateral cerebellar lesions have never been noted to produce obvious cognitive or emotional defects.
All the circuits detailed in this paper are laterosymmetrically replicated. Four primary translateral links integrate the two hemispheres. The nucleus reuniens links the two thalami in the environs of the paracentral and mediodorsal nuclei. The commissure and body of the fornix link the hippocampal formations with contralateral septal nuclei, thalami, and mammillary bodies. The anterior commissure links much of the temporal lobe with contralateral temporal regions (it also bears rhinencephalic data allowing some mammals to use ``binosal'' location). Finally, the corpus callosum (present only in placental mammals) is a very large bundle of some 200 million mostly slow-conducting fibers which link the essential entirety of the two cortical hemispheres. Many of these fibers interconnect homologous regions, and such fibers are mostly inhibitory. There are no fibers which directly connect contralateral corpora striata; any interaction between them is through at least one intervening nucleus and in general more than one. However, some corticostriatal fibers cross through the corpus callosum.
The alien hand syndrome is seen in patients with severed corpora callosa, and consists of willful limb movements initiated by the non-dominant hemisphere, but verbally reported by the dominant hemisphere to be unintentional, or indeed contrary to intention. This syndrome (and much other evidence, particularly involving patients who have undergone hemispherectomies) indicates that a coherent and complete system of consciousness, cognition, memory, goal structure, and action, exists in a single hemisphere. The manner in which the two complete conscious systems are fused into a single, cooperating consciousness, certainly depends on the corpus callosum, but this is hardly a full explanation. Clearly, the anterior commissure, fornix, nucleus reuniens, and interhemispheric links through brainstem nuclei, are insufficient to create any substantive coordination between the cerebral hemispheres. This suggests that the thalamus, as a node in the critical circuits of higher thought, serves largely as a collection of non-plastic, simple, fixed transformation, association, and relay nuclei - a solid backboard of sorts. The relative non-plasticity of brainstem nuclei has never been a point of serious contention.
Though laterosymmetry is salient from the perspective of gross anatomy, hemispheric assymetry is salient from a functional perspective. The predominance of homologous inhibitory fibers in the corpus callosum provides a first hint at the origins of this assymetry. This inverse correlation between the hemispheres necessarily conditions each hemisphere to precisely the dynamic not embodied by the other hemisphere. In morbid cases, this can lead to a dialectical relationship between the hemispheres, in which the hemispheres are proponents of conflicting cognitive models. In the ideal case, one hemisphere models those aspects of a phenomenon that are not modelled by the other, and the two hemispheres in concert embody a complete and detailed model. This asymmetry (symbiosis) extends to consciousness and memory themselves: those subjects that warrant conscious attention, but are not embodied by the conscious wavetrain of one hemisphere, are often embodied in that of the other hemisphere. A particular component of a memory constellation is often more efficiently and effectively embodied in one or the other hemisphere, and memory constellations routinely traverse the hemispheric boundary. Excitory callosal fibers linking certain regions of contralateral temporal cortex, if identified, would constitute a clear neurophysiological correlate of memory constellation bilateralization.
The memory coordination circuit (MCC) is responsible for the temporary registration of information so that it may come to be embodied through changes to myeloarchitecture, synaptic transfer functions, and cell body transfer functions, in isocortex. The organic components of the circuit extensively process the information to frame it in a manner suited to registration in long term memory. Many such frames are processed simultaneously, though of course there is a limit to the number and complexity of memories that can simultaneously be handled by the MCC. These frames are often episodic, constituting linked temporal sequences of world state fragments (qualia complexes, or equivalently, memory constellations), and processing of often non-temporal causal or other associative linkages of qualia complexes are de rigeur. These qualia complexes are often largely internal and non-sensory, constituting symbolic abstractions.
This circuit makes its instantaneous, highly processed contents available to consciousness directly, principally through multiple arrangements of dense reciprocation with frontal cortex, thereby acting as an auxiliary working memory.
The circuit is:
The MCC is not in the conscious signal path. At multiple loci, the conscious circuit and MCC junction, and the wavetrains they conduct assume postures of varying relationship. The most important such junctions are between the cingulate cortex and orbitofrontal cortex, and between the hippocampal formation and orbitofrontal. The thalamic nuclei implicated in the MCC are adjacent to the mediodorsal nucleus, and intrathalamic fibers probably allow for a further relation of the conscious and memory wavetrains at the thalamic level.
The insistence with which the MCC catalyzes changes in plastic neural substrate is largely a function of the emotional significance attached to the information. The hippocampal formation is made directly aware of this by projections from the amygdala, the septal region, the median raphe, the locus ceruleus, the basal nucleus of Meynert, and the lateral hypothalamus. The anterior nuclear group receives the mammillothalamic tract, bearing emotional information from the hypothalamus. Cingulate cortex is innervated by the amygdala and the septal region, and by the same diffuse modulatory systems that reach the hippocampal formation. Thus, at each node of the MCC, emotional information is a direct modulator. Moreover, the areas to which the MCC acts as an effector are directly aware of emotional information through broad amygdalocortical projections to temporal, insular, visual, somesthetic, and frontal cortex, and by innervation by the various diffuse modulatory systems. The MCC is the preeminent mediator of complex affect, as discussed below in section 3.4.7.
The mechanism by which the MCC mediates the transduction of qualia complexes from circulating frames to long term memories is likely as follows: (1) a qualia complex enters the MCC and begins circulating. (2) The MCC, through its broad connectivity with cortex, projects signal patterns that catalyze changes (changes in transfer function) therein (more on this below). (3) The MCC continuously measures the difference between the qualia circulating in the MCC, and that received from the implicated portions of cortex within which imprinting is progressing (this region is stimulated for the duration of imprinting), and as the difference tapers off, the MCC resources dedicated to the qualia taper off, until (5) The qualia is fully imprinted in cortex (long term memory), and vanishes from the MCC until it is implicated in a subsequent memory operation.
In a slight variation on the general mechanism of long term memory construction, the MCC continuously compares actual world state (including internal mental state) to the world state predicted by memory, and refines memories to improve the match, with the reinforcement signal diffused via the nucleus accumbens septi. The MCC also diffuses match/mismatch signals in various manners that are consciously perceived, as discussed below in section 3.4.6.
While the MCC involvedly analyzes consistency and effects changes to improve it, the continuity (subjective causality) that is a salient aspect of consciousness is embodied principally by the conscious circuits that involve frontal cortex and the corpus striatum, and inconsistencies are of course also detected directly by consciousness. The role of the memory coordination circuit is clearly circumscribed. Extensive bilateral ablation of the hippocampal region (as in the famous case of H.M.), while completely interrupting the circuit and abolishing memory refinement and construction, results neither in gross cognitive deficits nor in a breakdown in the subjective continuity of consciousness.
The precise manner in which the MCC (circulatory) and isocortical (transfer function long term modulation) representations of the qualia complex are compared is key to understanding the total memory system. Clearly the two representations must be compared in the same domain. The domain of comparison is probably intermediate: the circulating signal and the signal resulting from stimulation of the corresponding isocortical memory substrate must be projected to a single field in which they are compared (algebraically). Furthermore, it seems likely that the MCC has connectivity with the whole of this projection field (a convolutional arrangement), while connectivity between it and isocortex is likely significantly sparser (it is simply anatomically impracticable to have yet another organ with isocortical convergence at the level of the conscious circuit's). The cingulate gyrus is the strongest candidate I have identified for the organ that contains the comparison field.
Thus, the MCC's memory construction activity is likely mediated principally by cingulate cortex. Many candidate memory constellations enter the MCC from a region of temporal cortex at which projections from all sensory modalities converge, though clearly other regions - particularly, frontal cortex - feed directly into the MCC. Within the MCC, candidate memory constellations are extensively gated and processed, and heavily modulated by emotional context. Cingulate cortex mediates a prolonged simultaneous excitation, probably in synchronized pulses, of those cortical loci which will form nodes in a memory constellation, forming a constellation handle in temporal cortex or possibly in an adjoining region. As described above, a feedback control system drives the intensity and duration of excitation. The pattern of the excitation is likely also tailored by this feedback control system. This theory predicts that cingulate cortex will be found to have large, dense projections to most, or all, regions of isocortex that can be components of memory constellations. The cingulate cortex also coordinates integration of non-cortical regions, particularly of the amygdala, into memory constellations.
Memory constellations are cognitive models, and in fact all cognitive models embodied in neocortex are memory constellations. Goal structure embodied in frontal cortex is itself a set of cognitive models, and thus actually consists of memories. Like all other cortical memories, these goals come to be embodied through the action of the MCC. Frontal projections to and from components of the MCC serve much the same role that temporal projections do. Moreover, the process whereby the MCC refines the predictive accuracy of non-goal models applies likewise to goal models. Thus, the memory coordination circuit plays a vital role in the continuous validation, invalidation, and adjustment of goals. It is principally by this process that a tendency toward consistent, integrated goal structure is engendered.
The lateral dorsal nucleus is considered to be a caudal extension of the anterior nuclear group, and in addition to its primary projection to the cingulate gyrus, it projects to Brodmann area 5. Hints at the significance of this are given below in section 3.3.3.
The midline thalamic nuclei - the paraventricular nucleus, central nuclear complex, and nucleus reuniens - are clearly implicated in memory coordination and emotional entraining. According to Carpenter, these nuclei all project to the amygdala, some of them "may" project to the anterior cingulate cortex, and various fibers "are thought" to relate them to the hypothalamus. Also, the midline nuclei participate in the "recruiting response" described in section 3.1.1, underscoring their intimacy with consciousness. The midline nuclei may be a crucial pathway by which consciousness and memory coordination are linked.
Four contiguous cortical regions, the temporal (minus primary and paraprimary auditory areas), the insular, the posterior and lateral parietal, and the lateral visual, provide the basic semantic backdrop for consciousness and for the MCC, and gateway to domain-specific regions of sensory cortex. These extremely plastic regions are intimately and reciprocally interconnected with each other, with the frontal lobe, with the cingulate cortex, and with the neostriatum. Without the circuits these regions form, long-term memory would be essentially non-existent, so consciousness would be largely meaningless.
As mentioned in the previous section, temporal cortex contains a region that projects to the hippocampal formation including the hippocampus proper, and receives inputs from all sensory modalities. This system feeds a complete world state to the hippocampal region, and the connectivity also underscores the suitability of temporal cortex as a store of memory constellation handles. This region of temporal cortex also feeds memories to the hippocampal formation when they are activated, permitting the refinement activites described in the previous section.
Quite apart from the activities of the MCC, the memory constellations embodied by these regions are activated implicitly when circumstances, brought about either by external stimulus and therefore signalled by primary and paraprimary cortical regions, or resulting from the incidental evolution of a wavetrain circulating internally (often a combination of the two), activate components of the memory constellation. When component activations precipitate activation of memory handles, the constellations associated with those handles activate and may be incorporated into consciousness.
The associative portions of the parietal cortex - specifically, Brodmann areas 5 and 7 - are bound to the conscious wavetrain by multiple massive phylogenetic links. Premier among these is the rich reciprocal relationship of the orbitofrontal cortex with this area. The thalamus directly binds the cortical facilities of symbolic manipulation to the conscious wavetrain via projections from MD to the lateral posterior nucleus, thence to Brodmann areas 5 and 7. Finally, the caudate nucleus and putamen have reciprocal connections with all of parietal cortex, as with all other regions of cortex. A circuit involving areas 5 and 7 and the lateral posterior thalamic nucleus is probably fundamental to abstract symbolic reasoning, for example, set-theoretic thought and perhaps even finger-counting. Nonetheless, in practice this type of abstract thought draws on the causal and hierarchical specialties of the intimately related orbitofrontal cortex. Of area 5, Carpenter says "It has been postulated that area 5 contains the 'command apparatus' for limb and hand movements in immediate extrapersonal space. The 'command' hypothesis suggests that the cortical pathway from area 5 to area 4 is involved in initiating limb and hand movements." This underscores the intimacy (even indistinguishability) of areas traditionally thought of as motor, cogitative, and receptive.
A circuit involving the pulvinar of the thalamus may facilitate subconscious associational activation of memory constellations in reaction to sensory input. I am struck by the pulvinar's extensive projections to modal integrative (intradomain association) areas of sensory cortex and to wide areas of temporal cortex, and its innervation by the superior colliculus, itself a polymodally integrative brainstem sensory nucleus with a cortical arrangement. These projections may comprise a system which primes the cortex so that it will be more readily able to provide information on a demand or interrupt basis to the conscious wavetrain upon amalgamation.
Because the pulvinar's connections with visual and auditory cortex are broad, reciprocal, and topographically regular, the pulvinar may form a node in the circuit which implements the "rendering" capability of the mind - pivotal in providing for the capacity to dream. It is striking that these rendering activities are mutually exclusive with the environmentally-oriented priming described in the previous paragraph - the daydreamer is in his own world. As has long been recognized, somatotopic nociception does not form an element in dreams, and if the pulvinar comprises the selectively dissociable switch which accounts for dreaming - while sleeping or daydreaming - it follows that nociception will not be dissociable, since the pulvinar neither directly sends nor directly receives somesthetic information. Dreams are almost exclusively an audiovisual phenomenon.
Inhibition of normal activity in the MCC is also central to sleep dreaming. There are two major consequences: a dream is usually remembered only if the waking state is achieved in a manner that interrupts or immediately follows the dream, and a dream is not internally constrained by the self-consistency requirements normally enforced by the MCC. Clearly, the latter is partly due to the former, since self-consistency is impossible when some of the very items subject to the constraint are no longer embodied anywhere in (or out of) the brain. The memory coordination circuit has altered and attenuated dynamics, particularly while dreaming, but also during each of the other phases of sleep. In some of the other phases, memory coordination may proceed in some specialized manner operating on isocortex. Nonetheless, attenuated memory coordination activity is probably one of several central and unifying phenomena responsible for the rejuvenative effects of sleep. Indeed, the actions of the fully awake MCC are likely among the most metabolically taxing of any of the brain's routine dynamics, because of the broad, permanent physiological changes it effects.
The claustrum, a broad, thin lens of neurons situated amidst the white matter of the cerebral hemispheres, between the insular cortex and putamen, may implement a subconscious sensory FIFO (first-in first-out) buffer. The claustrum is segmented into regions dedicated to the auditory, visual, and somesthetic domains, and each of these regions has a regular topographic arrangement reciprocally relating corresponding regions in sensory cortex. It is cytoarchitecturally thalamic. My proposal is that fibers from sensory cortex feed a constant, essentially undigested stream of sensory data to the claustrum. The claustrum acts as a backboard much as the thalamus does in the conscious circuit. On an interrupt basis, therefore, raw data about very recent sensory input can be replayed with particular attention to aspects not relayed by the initial digested stream supplied to consciousness. Once the raw data is desired, the claustrocortical circuit can be made to reverberate the same raw data for a substantially longer time, perhaps in the tens of seconds, to the exclusion of new sensory data buffering. This mechanism may play an important role in the auditory loop. Conceivably, the reciprocal circuits of the pulvinar and those of the claustrum are used to implement something akin to register renaming or double buffering (both of these terms are borrowed from computer architecture - the first is a mechanism whereby active and latent information can be swapped to make access to the latent information more rapid, the second is a mechanism whereby the future state of an image train is computed and built up in an offline manner, so that it is ready for presentation once the future has become the present).
Note that, though I occasionally identify morbidities explicitly, there is a vast spectrum of dysfunctional deviations from the emotional dynamics enumerated below, many of which are associated with recognized mental illnesses. There is a similarly vast spectrum of morbid combinations of these emotions, all of which can occur completely in the absence of specific (DSM-IV et al.) mental illness, and all of which are consequences of the inherently self-contradictory total emotional dynamic. Emotions - all of them - are in constant interplay with each other, and their total dynamic is dauntingly complex and subtle. Moreover, there is no legitimate boundary between cognition and emotion, a reality that becomes particularly clear when training signals (reward/reinforcement) are treated at the level of neurophysiology. Total internal consistency in the corticostriatal system can be asymptotically approached, with rare individuals attaining this level of consistency as a practical matter, but many of the organs that orchestrate emotions are wholly or largely insusceptible to alteration and often mutually contradictory in their postures. The corticostriatal system accommodates these inconsistencies through detailed modelling (including internally directed goal structure), internal compensation, and compensatory modulations directed at the offending organs.
This circuit is strikingly reminiscent of the conscious circuits, and integrates primitive directed emotion with consciousness.
This circuit is strikingly reminiscent of the MCC, and integrates data relating to primitive metabolic drives into memory construction and refinement.
It is not possible to understand emotion and its manner of influencing consciousness without understanding the major connections of the amygdala. I provide here an overview of the amygdala's interconnections and their functional significance, paying particular attention to their impact on consciousness. The amygdala (possibly in necessary combination with some of the nuclei of the basal forebrain, particularly the septal nuclei and nucleus accumbens septi) modulates the activities of other brain organs to implement the five primitive amygdalar emotions: fear, anger, craving, disgust, and protection. These emotions are not exclusive, and can coactivate in any combination - though some combinations are morbid. Moreover, signals representative of these five primitive emotions are far from the complete lexicon of amygdalar output.
Fear activates when the amygdala perceives that a threat to a goal perceived by the amygdala exists. Anger activates when it perceives that such a threat exists that can be surmounted with aggression. Craving activates when it perceives that consumptive or non-destructive action directed toward an object can satisfy a goal perceived by it. Disgust activates when it perceives that approach toward an object can produce injury to a goal perceived by it. Protection activates when it perceives that a threat exists to an object that enables fulfillment of a goal perceived by it. An object can be animate or inanimate. Disgust and craving normally mutually inhibit. Fear, anger, and protection, often costimulate.
The amygdala is responsible for mediating a certain type of fascination. The domain of such fascinations is difficult to circumscribe, though its primary purpose is to draw attention to someone with whom the individual may fall or has fallen in love. It can also draw attention to inanimate objects that the amygdala perceives are crucial to satisfaction of other amygdalar goals. Fascination is a gateway to obsession, and indeed the amygdala is responsible for some, and perhaps most, obsessions. Fascination is not an emotion, but rather a cognitive imposition on consciousness, with an emotional periphery.
The amygdala consists of 13 nuclei, including a primitive cortical nucleus. Its organization is such that it is capable of rudimentary autonomous cognition, embodying cognitive models including goals, and transducing sensation (afferent connections) into action (transmitted via efferent connections) in a complex fashion. It has a complex internal state, which is driven not only by instantaneous input, but by a lifetime of prior inputs. With its extraordinarily broad connective architecture, the amygdala constitutes a brain within a brain, with a pivotal impact on other brain structures and the mental processes they support.
The basolateral nuclear group of the amygdala is largest, and receives audiovisual and somesthetic signals from the thalamus and neocortex. The smaller corticomedial nuclear group receives olfactory signals from the paleopallium of the amygdala. These nuclear groups act in receptive and interpretive roles, determining emotional responses based on received signals. The central nuclear group is driven by the other nuclei and orchestrates behavior based on their emotional decisions, particularly through modulation of the hypothalamus and brainstem autonomic centers. The 13 nuclei of the amygdala are intricately linked with each other.
The midline nuclei of the thalamus (paraventricular, central nuclear complex, and nucleus reuniens), already mentioned above in section 3.3.1 (discussion of the MCC), are clearly key in integrating amygdalar emotion, memory coordination, and consciousness. Not only do they participate in the recruiting response and project to the amygdala ipsilaterally, they are also projected to by the basolateral amygdaloid nuclei and the periamygdaloid nucleus. These regions of the amygdala also project to the magnocellular portion of the mediodorsal nucleus, thereby directly modulating the conscious wavetrain at the thalamic level.
Fine myelinated and unmyelinated fibers are also thought to relate these amygdalar regions to the hypothalamus, and the corticomedial amygdala projects to anterior and ventromedial hypothalamic nuclei via the stria terminalis, providing avenues for emotional state (particularly those related to olfaction) to influence endocrine and metabolically oriented drives and activities. The rostral half of the hypothalamus projects to all amygdaloid nuclei except the central nucleus, chiefly from the ipsilateral lateral area (with the ventromedial hypothalamic nucleus projecting mainly to the medial amygdala), providing a pathway for metabolically oriented drives to influence emotional state.
The central nucleus of the amygdala has reciprocal connections with brainstem nuclei that regulate breathing (the parabrachial nuclei), heart rate (the nuclei of the solitary fasciculus), and digestion (the dorsal motor nucleus of the vagus). Thus, the amygdala is able to orchestrate the basic visceral component of the defense reaction (involved particularly in fear and anger) in an essentially direct manner.
The amygdala projects widely to the neostriatum, within those regions thereof that are implicated directly in the conscious neural pathway. In particular, the basal lateral nuclei (known to be crucial to the defense reaction) project to ventromedial portions of the caudate nucleus and to the putamen, with modest contralateralization via the anterior commissure (constituting an extra-collosal pathway whereby contralateral emotional state is entrained). There are likely unconscious regions of the neostriatum that are innervated by the amygdala, and conscious regions that are not. The latter constitutes a relatively dispassionate component of the conscious drive.
The amygdala projects to the magnocellular nuclei of the substantia innominata, so that emotional state directly modulates the cholinergic suffusion of the entire cortical mantle. It projects to cingulate cortex, the hippocampal formation, the subiculum, and entorhinal cortex, so that emotional state directly modulates the memory coordination circuit at multiple loci, and hence, the manner in which long term memories are constructed - particularly, their weight and prioritization.
The amygdala also projects directly to wide regions of isocortex, including the frontal lobe (thereby directly modulating the conscious wavetrain at a third junction), insular and almost all regions of temporal cortex, visual cortex, and parietal (including somatosensory) cortex. These links also allow integration of the amygdala (and hence, amygdalar affect) into memory constellations.
The amygdala's linkages with the midline nuclei, the hippocampal regions, cingulate cortex, and the insular and temporal cortices, are the vital pathways whereby the amygdala drives the construction of long term memories and participates in their activation. These processes are often unconscious, and are not completely abolished even when the MCC is interrupted (for example, by bilateral hippocampal ablation). This system is responsible for configuring the brain to react in an emotionally appropriate and anticipatory manner to stimuli that have had an emotionally significant impact in the past. The amygdala operates as a separate coordinator of memory construction and recall, and this - combined with its sensory window, described immediately below - results in the strange effect of motor and metabolic reactions to a complex stimulus preceding conscious awareness of it.
The amygdala is fed a stream of audiovisual sensory information, both from unimodal association cortices (within the regions identified above), and from sensory nuclei of the thalamus. These inputs, combined with the long-established olfactory input from the paleopallium to the corticomedial nuclei, supply the amygdala with a window on the outside world. Sensory stimuli can (and often do) directly precipitate emotional, metabolic, and autonomic motor reactions, absent initial conscious involvement, and even completely absent initial neocortical involvement. In fact, the amygdala can autonomously categorize facial expressions to identify the emotional state of other individuals (it is in fact vital in performing this task), and can distinguish individuals one from another. These amygdalar decisions can precipitate fixed (modal) action patterns, e.g. responsive facial expressions, through as yet unenumerated but clearly unconscious pathways. Meaningful social interaction can thus occur entirely outside consciousness.
The amygdala's private memories are not directly accessible to the conscious mind, and are managed internally and independently. The amygdala establishes stimulus-response pairs autonomously, and the conscious mind is subjected to them as an externality. The conscious mind learns of the amygdala's stimulus-response pairs in a subsequent and separate act. Amygdalar memories are not immutable and permanently established. Each time a memory is activated (a stimulus-fear pair, for example), the memory must be reconsolidated through subsequent metabolic activity. If reconsolidation of amygdalar memories is inhibited after their activation (through pharmacological means, for example), the memory is dismantled (the stimulus-fear pair vanishes). This result was reported in a paper that appears in Nature, 2000-Aug-17, by Karim Nader, Glenn E. Schafe, and Joseph E. Le Doux, ``Fear memories require protein synthesis in the amygdala for reconsolidation after retrieval''.
The amygdala is a heuristic engine that, largely by hereditary predisposition, models natural physical principles, particularly in terms of competition and cooperation, and generally by creating pressure to behave in a manner the amygdala adjudicates is conducive to long term (hereditary) biological survival. Natural physical principles are insusceptible to amendment, and the amygdala essentially delivers information to the rest of the brain according to its own rules, rules which constitute its partially phylogenetic model of natural physical principles. The amygdala is, of course, quite far from foolproof. Moreover, inputs to the amygdala from the (extremely plastic) corticostriatal system greatly influence the amygdala's models and decisions, which themselves greatly influence the models and decisions of the corticostriatal system.
The hypothalamus is the seat of metabolic and endocrine maintenance and drive, and is an engine that models the natural physical principles that impinge on biological survival at the level of internal somatic and procreative processes. Through neural projections and endocrine synthesis, it coordinates actions conducive to survival according to those models. In particular, the hypothalamus regulates body temperature (driving sweating and shivering, and creating sensations of diffuse hotness (painful, desire for cold) or cold (painful, desire for hotness)), sugar and fat level and metabolism (driving endocrine balance processes, and creating sensations of hunger (painful) and food satiety (pleasurable)), water balance (driving balance processes, and creating sensations of thirst (painful) and fluid satiety (pleasurable)), and sleep rhythm (entraining the excitation centers (discussed below in section 3.4.6), and creating sensations of sleepiness (accompanied by yawning, and vaguely painful when prolonged) and pleasure on the threshhold of sleep's embrace.)
The subject of a hypothalamic drive is a class, and not an instance. The drive precedes appearance of the external object or objects by which the hypothalamic drive can be fulfilled, sometimes by a long duration. Thus, hypothalamic drives are somewhat the opposite of amygdalar emotions, whose subjects are instances and which activate only after the subject is perceived.
From Carpenter: "The lateral and posterior hypothalamic regions are concerned with the control of sympathetic responses. Stimulation of this region, especially the posterior portion from which many descending efferents arise, activates the thoracolumbar outflow. This results in increased metabolic and somatic activities characteristic of emotional stress, combat or flight. These responses are expressed by dilation of the pupil, piloerection, acceleration of the heart rate, elevation of blood pressure, increase in the rate and amplitude of respiration, somatic struggling movements, and inhibition of the gut and bladder." The sympathetic reaction can also be evoked through stimulation of the amygdala, and the amygdala and hypothalamus are tightly integrated in their activities.
The hypothalamus plays a vital role in directing release of growth hormones, and in a gender-dimorphic manner, the release of hormones that drive secondary sexual characteristics. Ovulation (and menstruation) cycling is driven by the preoptic area, and the corticomedial nuclear group of the amygdala is integrated into this system via the stria terminalis (presumably with the intimate participation of the Bed nucleus). This linkage is probably wholly responsible for the phenomenon of cycle synchronization among women in prolonged proximity.
Pleasure and pain are qualitatively different from the emotions orchestrated by the amygdala, and wholly different from the drives orchestrated by the hypothalamus. Like the five amygdalar emotions (fear, anger, craving, disgust, and protection), they are experienced in response to stimuli, along a continuous range of intensity. However, whereas amygdalar emotions can be thought of as vectors - with a discrete orchestrating agent (the amygdala) clearly representing the subject of the emotion - pain and pleasure do not have a unique, distinguished, symbolically coherent initiating agent, and thus no regularized manner of representing the subject of the emotion exists. The subject is in many cases first represented after the emotion has been consciously perceived, though when a cognitive model predicts the pain or pleasure the subject is clearly known in advance. With amygdalar emotion, the conscious mind endeavors to recreate the unconscious but pre-existing amygdalar model. With pain and pleasure, the initial origin of the emotion can be direct-mapped sensory receptive fields or archaic non-plastic neural structures which do not embody any substantive associative (meaningful) models, but are simply phylogenetically preconfigured to broadcast the emotion upon receipt of signals relaying information of certain sensory or endogenous stimuli.
Pain and pleasure, though clearly emotional from the subjective perspective of consciousness, are also the fundamental training signals that mold the plastic neural substrate. This was hinted at above in section 3.1.2 (discussion of the substantia nigra as a motor reinforcement diffuser) and 3.3.1 (discussion of match-mismatch reinforcement by the nucleus accumbens septi in the memory coordination circuit), and will be explained in much greater detail below.
The somatotopic nociceptive system constitutes a pain system with a very specific neurophysiological correlate. This specific type of pain, with its clear loci of causation (subjects), precipitates the general type of pain that is being discussed in this section.
Though there is no distinguished anatomical seat of pleasure, there is nonetheless a set of organs intimately associated with it. The ventral tegmental area (VTA) is the most important of these, and is discussed at length below. Within the telencephalon, the septal nuclei and the nucleus accumbens septi are both mediators, with the former constituting the essential orchestrator of the sexual orgasm.
Viewed narrowly, the sexual brain consists of the septal region, the Bed nucleus of the stria terminalis (a component of the amygdaloid nuclear complex that embodies gender identity), the preoptic region of the hypothalamus (embodying sexual orientation and thus a component of sexual drive), the central and lateral areas of the hypothalamus (completing the hypothalamic sexual drive apparatus), the basolateral and corticomedial nuclear groups of the amygdala (deciding whom and when to crave sexually, and orchestrating some aspects of sexual behavior), and the central nucleus of the amygdala (orchestrating brainstem autonomic and some hypothalamic aspects of sexual behavior). Viewed broadly, the sexual brain consists of the entire brain, which evolved almost entirely in a progressive optimization for individual procreative performance. Beyond orchestrating fleeting sexual attraction and performance, the basolateral and corticomedial amygdala are likely key in deciding when and with whom to fall in love - a decision nonetheless clearly made in conjunction with other brain structures, particularly the corticostriatal system. This phenomenon is discussed in great depth below, in section 188.8.131.52.
The medial septal nucleus is linked with the amygdala, directly interrelating the amygdala with potentially intense pleasure with a sexual character. The hippocampus projects to the lateral septal nucleus, and the medial septal nucleus projects to the cingulate gyrus and back to the hippocampus. These connections intimately relate the MCC with potentially intense pleasure with a sexual character. The septal nuclei also project to the lateral hypothalamus, allowing modulation of endocrine activity and metabolic drive, and their projection to the midbrain tegmentum is likely pleasure-suffusing and pain-suppressing. Septal projections to the habenular nuclei provide a direct pathway whereby the septal nuclei modulate visceral state.
Pain and pleasure are scalar influences on the mind, with an extremely complicated and distributed neurophysiological correlate. Either of them at faint or moderate intensity enhances the power of consciousness, and either of them at great intensity erodes the power of consciousness. Since pain and pleasure are broadcast scalars, their incidence evokes a diverse response from the neuraxis, with each distinct organ (and modules and subdivisions therein) responding in a manner that is idiosyncratic and, outside the cerebral cortex and corpus striatum, substantially phylogenetically predestined. In the corticostriatal system, the manner of response is phylogenetically predestined only at very low levels, with plasticity causing pain and pleasure to have highly variable and context-dependent effects at higher levels. The subjective experiences of pain and pleasure are the consequence of the manner in which organs associated directly or indirectly with consciousness respond to the scalar broadcast signal. The manner in which a particular organ responds can be extremely complicated, particularly in that it can vary with the envelope and recurrence of the broadcast signal, and with context derived from the senses, from memories, and implicit to current mental state.
Two specific neurotransmitters, substance P and enkephalin, are dedicated to pain and pleasure (respectively). These neurotransmitters are not, however, used in the broadcast mechanism, though they appear to be used in narrowcasting roles (diffusion within individual organs and between intimately related pairs of organs).
Certain brain structures, particularly the substantia nigra (SN), VTA, midbrain periaqueductal gray (PAG), and the raphe nuclei, are active sites for substance P and enkephalin and configured to diffuse signals throughout much of the neuraxis. In the case of the raphe, this arrangement is not actually associated with pain and pleasure broadcasting, but simply with specialized (somatotopic nociceptive) analgesia, at a greater level during wakefulness so that nociception during sleep is heightened.
The PAG does not in fact play a role in pleasure and pain diffusion, but its characteristics are worth noting. From Carpenter: "[the PAG] has been implicated in central analgesic mechanisms, vocalization, control of reproductive behavior, aggressive behavior, and mechanisms of upward gaze. Afferents to the PAG arise from the hypothalamus, the brain stem reticular formation, the raphe nuclei, the locus ceruleus, and the spinal cord, and many of these regions receive reciprocal connections from the PAG." The PAG also has connections with the central nucleus of the amygdala. The PAG, like the raphe, has analgesic projections that descend to spinal levels. Beyond observations regarding its columnar organization and specific functionalities, the PAG clearly lacks the connective diversity necessary for it to act as a general purpose pleasure-pain diffusion center.
VTA plays precisely the role for which the PAG is unsuited. VTA reciprocates with frontal cortex, cingulate cortex, the neostriatum, the amygdala, the nucleus accumbens septi (n. accumbens), the hypothalamus, the globus pallidus, and parts of the hippocampus. It diffuses dopamine, a neurotransmitter loosely correlated with pleasure wherever it occurs, and always associated with pleasure when it originates with the VTA. Stimulation of VTA has been found to produce a diffuse sensation of pleasure, and this locus is implicated in models of euphoric drug action.
Both the neostriatum and the frontal cortex have the connective diversity necessary for detecting localized pain and pleasure and gating scalar globalizations based thereon, and both reciprocate with the VTA. This, combined with VTA's connectivity with unconscious structures directly involved in goal-directed behavior, make the VTA by far the strongest candidate for a pleasure (reward) diffusion nexus. The neostriatum and neocortex are certainly the principal conscious regions within which the lessons of pain and pleasure are represented, and the amygdala, the principal unconscious organ within which these lessons are represented. Though VTA diffuses the reward signal in an essentially indiscriminate manner, a particular region upon receipt of the signal will react only if it is already neurodynamically active (the reinforcement signal is neurochemically inhibitory, so that an inactive region is essentially unaffected). Since the regions active at a given moment tend to be involved in some way in the cause of the reward, reinforcement is roughly confined to those regions that ought logically to be reinforced.
N. accumbens, through innervation by VTA, is influenced by, though not in direct synchrony with, the broadcast pleasure signal. The diffuse dopaminergic innervation by n. accumbens of the hippocampal region in particular is indispensable for the registration in isocortex of accurate models of reality, coordinated by a properly functioning MCC. Prefrontal cortex and the amygdala are also innervated by n. accumbens, and portions of the hippocampal formation are innervated by VTA. The hippocampal region is active for enkephalin itself, seen in projections from entorhinal cortex to the hippocampus, underscoring the importance of reinforcement signals to memory coordination. Dysfunction of n. accumbens or its afferent connections (particularly, from the subiculum) results in schizophrenia, a condition in which the memory coordination circuit discriminates in a manner reflective neither of internal reality nor of external reality. Schizophrenia is caused by a morbid decorrelation between accumbal reinforcement and the memory coordination circuit's measure of predictive accuracy, and between signals of the VTA and those of n. accumbens. The other nuclei of the septal region also reciprocate with the hippocampal region (and the amygdala), and probably play a subsidiary role in this training apparatus.
The SN reciprocates massively with the corpus striatum, and innervates the ventral anterior nucleus pars magnocellularis and the mediodoral nucleus, paralaminar portion, both of which are components of the conscious circuit. The various afferent connections of the SN are integrated in some manner in the reticular portion of the nucleus. The SN appears to play a vital role in diffusing dopaminergic reinforcement signals within the subcortical associative motor system. This reinforcement signal does not appear to play a significant role in diffusing signals subjectively perceived as pleasurable, nor in diffusing reinforcement signals important to the construction of conscious goals and models. Instead, SN reinforcement signals are modulated by measuring the difference between conscious action intention (determined from striatonigral input) and realized action (determined from pallidonigral input). SN does not have any direct links to VTA or n. accumbens, though it is innervated by the raphe and reciprocates with the pedunculopontine nucleus (neither of which is associated with reinforcement diffusion). Nigral dysfunction does not result in the thought disorders associated with dysfunction in VTA and n. accumbens. However, extreme dysfunction in SN causes a total suspension of consciousness, involving complete abolition of autonomously initiated action and a complete suspension of subjective time. Apparently, without nigral modulation, the corpus striatum becomes static, abolishing consciousness. Parkinsonism is a milder nigral dysfunction.
Dopamine is an inhibitory neurotransmitter, and squelches excitory afferent signals. Substance P, the transmitter dedicated to pain, is excitory. However, it appears unlikely that substance P itself is used for pain diffusion in a manner analogous to the dopaminergic diffuse modulatory apparatus. Instead, a variety of excitory neurotransmitters (e.g. acetylcholine and noradrenalin, both of which are diffused continuously by the excitement system, described below) likely act in this role. This is unsurprising, since indeed it is enkephalin that is dedicated to pleasure, not dopamine itself. Diffuse pain (negative reinforcement) is likely the result of downward modulation of the dopaminergic diffusion apparatus, sometimes in combination with activation of diffuse excitory pathways projecting coincidentally or in close proximity.
The purpose of pleasure and pain is to modulate mental representations so that pleasurable behaviors are embraced and painful ones avoided. Though experience can significantly color the predication of pain and pleasure precipitation, and in certain domains is the dominant determiner, viewed broadly the relationship between stimulus and the pain and pleasure responses is principally phylogenetic, with the phylogenetic preferences of the brainstem nuclei, amygdala, and hypothalamus playing central roles. Thus, pain and pleasure are the preeminent mechanisms by which genetic endowment is transduced to representations in plastic neural structures, particularly in the neostriatum and neocortex (the vital plastic components of the neurophysiological correlate of consciousness) and in the amygdala (which has significantly more genetic predestination than the telencephalic NCC).
Excitement is the most primitive emotion of all, and is essentially a measure of and influence on total mental activity level, with certain differential activations of the organic substrate implementing such phenomena as sleep. Whereas pain and pleasure are bipolar, set in opposition to each other (though not at all mutually exclusive in their activation), excitement is a monopole. Unlike pain and pleasure, though, excitement is certainly modulated from specific loci in the neuraxis - specifically, the basal nucleus of Meynert and pontomesencephalotegmental cholinergic complex (cholinergic suffusion), substantia nigra (SN) and ventral tegmental area (VTA) (dopaminergic suffusion, substantially decorrelate from other diffusers), raphe nuclei (serotonergic suffusion), locus ceruleus (noradrenergic suffusion), and nuclei within the lateral and tuberomammillary hypothalamus (histamine, GABA, and different peptides (alpha-MSH, adenosine, CCK, VIP)). These systems of projection are known as diffuse modulatory systems.
The precise myeloarchitecture of these organs is instructive.
The basal nucleus of Meynert is innervated by the amygdala and by insular, temporal, pyriform, and entorhinal cortex, and innervates the amygdala and the whole of the cerebral cortex. The pontomesencephalotegmental cholinergic complex (consisting of the pedunculopontine (PPT) and laterodorsal tegmental (LDT) nuclei) innervates the PAG, VTA, dorsal raphe, dorsal thalamus, lateral hypothalamus, SN, basal ganglia, hippocampus, and portions of frontal cortex, and is innervated by SN, the medial pallidal segment, and portions of the cerebral cortex. It also projects to the nucleus reticularis pontis oralis (RPO), which itself has unknown chemistry, but which in combination with the PPT and LDT constitutes the REM-on system.
The substantia nigra is innervated massively by the neostriatum, but also by the globus pallidus, the subthalamic nucleus (implicated in motor buffering and learning), and the raphe nuclei, and innervates the neostriatum massively and the thalamus - in particular, the ventral anterior nucleus pars magnocellularis and the mediodoral nucleus, paralaminar portion, both of which are components of the conscious circuit. SN, as noted above, is a motor learning reinforcement diffusion center, making it a special case among diffuse modulator centers. VTA reciprocates with the neostriatum, frontal cortex, cingulate cortex, amygdala, globus pallidus, nucleus accumbens septi, and hypothalamus, and its activation is decorrelate with sleep state. VTA, as noted above, is a global pleasure (reward) diffusion center, making it a special case.
The raphe nuclei innervate the substantia nigra, the locus ceruleus, the hypothalamus, the intralaminar thalamic nuclei (the rostral portion of which is a component of the conscious circuit), cerebral cortex favoring frontal cortex, the hippocampal formation, the neostriatum, and the amygdala.
The locus ceruleus broadly innervates neocortex, the hippocampal formation, the thalamus, the hypothalamus, and brainstem sensory and association nuclei, presumably to include the raphe, and in combination with the raphe constitutes the REM-off system.
The lateral and tuberomammillary hypothalamus diffusely innervate the cerebral cortex, and abolition of these inputs results in prolonged coma.
These nuclei are not only linked to vast realms of neural topography, including the whole of the neurophysiological correlate of consciousness, but also to each other (with the exception of the substantia innominata, which alone among these nuclei is telencephalic). They constitute a system by which excitement in general, and such phenomena as sleep in particular, are coordinated.
The substantia innominata, also called the nucleus basalis or basal nucleus of Meynert, is arranged so that protoemotional excitation expressed by the amygdala, reactions to emotionally meaningful odors (pheromones and other biological odors with great significance) expressed by the pyriform and entorhinal cortices, and the fact of memory constellation recruitment (a secondary effect) as expressed by insular and associative temporal cortex, arouse the whole cortex through cholinergic suffusion. This serves as another component of emotional diffusion, along with amygdalocortical projections and the effects of the emotional circuits detailed in 3.4.1 and 3.4.2.
Surprise is the sensation that accompanies subjective recognition by some portion of the brain that its model of reality is not in registration with reality. It is a jolt of excitement, but it is somewhat akin to pain and pleasure in its manner of operation. It is often accompanied by some degree of fear and some degree of pain. Relief is the sensation that accompanies confirmation that a model whose registration with reality was in doubt, is in fact in registration. Relief is a reduction in excitation. It is accompanied by a reduction or elimination of fear centered on the matter at issue (if any is present) and, if the model is consistent with fulfillment of a goal, by pleasure.
Surprise and relief driven by corticostriatal models are probably mediated in large part by the MCC, which has precisely the necessary dynamic and connectivity. See section 3.3.1, above, for details.
The principal corticostriatal emotions are hate, sadness, contentment, joy, shame, embarrassment, and amusement. With these emotions, there are neither specific anatomically localized dedicated initiating correlates (in contrast to the amygdalar emotions and excitation), nor specific neurochemically distinct correlates (in contrast to pain and pleasure). Like the amygdalar emotions, they have a fully represented and often conscious subject except in conditions of morbidity, and can activate in any combination, with some combinations being paradoxical or morbid. As in the pain and pleasure systems, the neostriatum is a vital component of the substrate for these emotions, but the frontal cortex (rostral to area 6) and the MCC are similarly important. This vast, distributed corticostriatal system is the linchpin.
The lachrymation and crying that (in the absence of successful corticostriatal inhibition) accompany intense sadness are evidently orchestrated by one or more phylogenetic loci, but they do not generate the sensation of sadness. They simply react to the condition of sadness. The same is true of embarrassment and blushing, of joy and smiling, and of amusement and laughter. For laughter in particular, a locus for coordination has been identified in the hypothalamus, and tumors disrupting this locus are known to create urges to laugh, but these urges are consciously perceived as irrational and unaccountable - that is, there is no sensation of amusement. Unconscious structures are intimately involved in the expression of each of these emotions, and in many cases are instrumental in arranging the corticostriatal system in such a manner that these emotions eventually precipitate, but they are not direct initiators.
These emotions are patterns of goal structure dynamics. Goal structure is the vital scaffolding of consciousness, its foremost organizing principle, and the foundation of personal identity. Nonetheless, corticostriatal goals can be formed and pursued unconsciously, impinging on consciousness in a subjectively mysterious manner. Such goals can be made conscious through exploration and experimentation by consciousness and by external actors.
Goals are a particular type of cognitive model, one that specifies actions that can and will be taken or avoided in order to attain a predicted future condition (which may, nonetheless, be identical to a current condition). This type of goal is embodied in the corticostriatal regions identified above, whereas telencephalic cognitive models that are not goals are embodied by other regions, in particular, the associative portions of temporal, parietal, and visual cortex, and possibly by the insular and cingulate cortices in specialized roles. Goals are intimately integrated with these non-goal models, and the foremost anatomical correlate of this integration is the massive reciprocation of the frontal cortex with the cortical regions just identified, through multiple, massive, discrete fasciculi (uncinate and arcuate linking temporal cortex, superior longitudinal linking parietal and visual, cingulum linking parahippocampal and adjacent temporal, and other links to those regions not innervated by these fasciculi).
Invalidation of a goal is painful, in contrast to invalidation of a non-goal model, which does not in itself tend to be painful. This distinction has a stark neurophysiological correlate. The VTA, seat of global reward and punishment diffusion, reciprocates with frontal cortex, the corpus striatum, the amygdala, and the telencephalic nodes of the MCC. It does not reciprocate with non-frontal isocortex, aside from cingulate (memory coordinating cortex). Thus, the non-goal cognitive models embodied in non-frontal cortex lack the connectivity to autonomously trigger global reward and punishment.
Because it is specifically and almost wholly responsible for
mediating goal structure dynamics (changes), and considering its
connective architecture, the MCC is clearly
integral to the corticostriatal emotional system. The VTA's efferents
to the hippocampal region and afferents from frontal cortex and the
neostriatum are vital pathways whereby the MCC
measures the destructive impact of its activities on goal structure.
When the MCC attempts to catalyze annihilation
of a goal, the affected cortical regions signal pain
None of the corticostriatal emotions are necessarily precipitated by the goal structure dynamic capable of doing so. In particular, a goal to inhibit the indicated emotional precipitation can often succeed in doing so.
Human goal structure is arbitrarily plastic, but inherently tends toward, though never achieves, total self-consistency and integration. A relationship of self-consistency between two goals is one in which fulfillment of one goal does not preclude fulfillment of the other or erode the degree and expectation thereof, though vitally, goals can be logically grouped (into larger goals) in such a manner that fulfillment of some logical combination of goals in the group obviates fulfillment of some of the group's constituent goals, or indeed specifies that certain goals be annihilated. Self-consistency between all pairs of goals constitutes integration of goal structure, which in its most thorough form constitutes an arrangement in which a single, distinguished goal sits at the apex of a single goal hierarchy that encompasses all other goals. This extreme degree of integration, while maximizing pleasure-driven self-motivation, is vulnerable in its concentration of significance in a single goal. In many cases fragmentation into a looser confederation of goal hierarchies is inevitable.
Like all cognitive models, goals are actually composed of probabilistic expectations, and logical combination and hierarchicalization of goals involves compositions of probabilities and not of sureties.
Goals come in many forms, the most commonly understood of which is a straightforward goal to bring about a condition through action. There are many other varieties. Perpetuation of an existing condition can be a goal. Preventing a condition can be a goal. A condition can be an internal mental state, arrangement, or process, a state, arrangement, or process of external objects, a mental state, arrangement, or process internal to another individual, a pattern of behavior or principle to which behavior adheres (a rule), or any combination thereof. Except in cases of morbidity, a goal cannot long exist out of registration with its subjective expectation of fulfillment. Thus, erosion or annihilation of the expectation that a goal will be fulfilled usually erodes or annihilates the goal itself, with a delay proportional in some manner to the significance of the goal.
A goal is often, though not always, something that is thought to cause or lead to pleasure or to the avoidance of pain, though it may be expected to involve pain or reduction of pleasure. In morbid cases, pain, self-injury, or suicide can be a goal. Goal fulfillment itself is pleasurable in proportion to the significance of the goal, completely apart from any other pleasure fulfillment of a particular goal produces. In proportion to the significance of the affected goals, evolution of subjective conditions such that goal fulfillment approaches in probability or time is pleasurable in proportion to the relative change in probability or time, and evolution such that it recedes is proportionately painful.
Goals are arranged in hierarchies, with a particular degree of fulfillment of a goal predicated on particular degrees of fulfillment of some combination of goals beneath it in the hierarchy. A particular goal can appear in a hierarchy more than once, and can appear in more than one hierarchy. A goal is significant in proportion to the number of goals that it is predicated upon, in proportion to the number and significance of the goals that are predicated on it (with downward adjustments to account for optional predication), in proportion to the volume of pleasure (integration of pleasure over all time) its fulfillment is expected to produce, in proportion to the volume of pain expected to result from a failure to fulfill the goal, in inverse proportion to the volume of pain its fulfillment is expected to produce, and in inverse proportion to reduction in volume of pleasure a failure is expected to produce.
Invalidated goals usually, and particularly when the goal was conscious, survive as memories (non-goal models). It is not clear if the cortical geography which embodied the goal while it was subjectively valid, is a potential component of the memory of the goal. It is far more likely that it is not. The memory is likely embodied by non-frontal cortex, and the frontal geography is recycled or effectively condemned. In any case, the links between the non-frontal representation of a goal and the invalidated frontal goal proper begin weakening as soon as the goal is invalidated.
Frontal recycling occurs through reconstruction, in the case of a goal whose significance was relatively minor. In the case of a goal whose significance was great, frontal geography can be occupied for an arbitrarily long time by a decaying corpse of sorts. Such geography is recycled only in the case of major plasticizing emotional trauma (though note that the invalidation itself is often a plasticizing emotional trauma), and is possibly reanimated (restored as a valid goal) in necessarily altered (and quite possibly horribly corrupted and inconsistent) form at a later time, also sometimes as a result of plasticizing emotional trauma.
The fundamental (though hardly orthogonal) dimensions of corticostriatal aptitude are:
Though the discussion of section 3.4 might lead the reader to conclude that the human corticostriatal system (and its thalamic backboard nuclei) is invariably subordinated to the whimsy of external emotional influences, as in animals, this is not the case. In some individuals, consciousness is of such power that non-corticostriatal emotional considerations (other than pleasure, which transcends boundaries) are substantially overwhelmed, and short term pleasure and pain are incapable of catalyzing substantive changes to significant goal structure. This is one of many fundamental characteristics that starkly divide humanity from other species. The characteristics that facilitate such a corticostriatal dominance are enumerated above.
The corticostriatal emotions are the ones that most readily and regularly lend themselves to sympathy (or, here equivalently, empathy). Sympathy is stimulated with those with whom an individual perceives a positive correlation of goal structure fulfillment (similarity of conditions which satisfy goals which may, themselves, actually differ), and inhibited with those with whom an individual perceives a negative correlation. Sympathy is an arrangement in which one individual temporarily treats the goal structure of another individual as his own, and experiences the emotions the other individual is or might be experiencing based on a model of the mental state of the other individual.
Viewed most primitively, sadness is the subjective experience of erosion or annihilation of a goal. When a significant goal is annihilated, grief (intense sadness) can result. The goals at issue are often intentions to maintain a condition. Such injuries usually take the form of loss of or damage to a material possession or another living organism, though they can also involve extremely intricate and vast social goals (as in politics, finance, industry, etc.). Subjective goal invalidations are not necessarily accurate, of course (c.f. Romeo and Juliet by Wm Shakespeare). Annihilation of a goal prompted by a hierarchically superior goal, either due to realization of the inferior goal's disposability, or due to satisfaction of the superior goal, leads to sadness either not at all, or at a greatly diminished level.
Disappointment is sadness due to erosion or annihilation of a goal that most often, though not necessarily, consists of attainment of a condition in the future that is not a present condition. It is not usually caused by annihilation of a significant goal (which usually produces grief), but instead, by erosion of a significant goal or annihilation of a minor goal. Disappointment with another person is erosion or annihilation of a goal that consists of behavior by that person. Grief and disappointment do not usually coactivate. Disappointment often prompts vigorous mental activity to quickly repair goal structure, whereas grief is of such magnitude that, typically, no such vigorous activity is attempted for the duration of grief.
Sadness is often experienced sympathetically, prompted by perception and contemplation of another's actual or potential sadness, or the causes thereof. Such sympathetic sadness is not, by itself, accompanied by any actual injury to the goal structure of the sympathizer.
Clearly, amygdalar emotions (in particular, anger, especially when an animate actor is identified (accurately or not) as responsible for the sadness) and pain (precipitated by those regions of the brain that participate in the particular collapse of expectation that produced sadness) regularly accompany sadness, with the latter accompanying it initially and waning, and the former usually appearing only subsequently, perhaps in response to the pain. These reactions of pain and anger can accompany subsequent recall of the collapse of expectation, at an arbitrarily later time.
Sadness also often modulates the excitement protoemotion in a downward direction, probably with a differential impact on the four main loci of excitement suffusion, broadly changing neurochemical balance.
Sadness is a phenomenon of goal structure injury and, since goal structure is a hierarchy, injury to a locus of goal structure can gravely impact massive regions of mind, cascading the injury in an often very rapid or nearly instantaneous manner. Serious injury to or destruction of a node high in a goal hierarchy is thus a serious neurophysiological event, with the potential to overwhelm - temporarily or indefinitely - the conscious mind's capacity to work effectively in a conscious, goal-driven manner. The amygdala, the septal region, and the loci of excitement suffusion, can be led to assume increasingly dysfunctional postures, as they are substantially released from disciplined corticostriatal control. In short, gross injury to goal structure (perception of broad goal structure invalidation) is the definitive personal failure. As the corticostriatal apparatus is forced into bankruptcy, the largely phylogenetic and unconscious goal structure of the amygdala and other extra-corticostriatal drivers becomes dominant. This, evidently, constitutes an arrangement in which the legacy reptilian mind has gained supremacy over the modern mammalian mind. Alarmingly, the phenomenon of falling in love actually constitutes just this type of gross injury, forced bankruptcy, and subordination of the mammalian mind, with the vital corollary that a new emotionally authentic goal structure tends to be hastily erected.
One manner in which a mind can recover from the morbidity of gross goal structure injury is through revisitation of the subject of the initial sadness - of the initial invalidation - with a determination to restore the expectation of satisfaction. When the morbidity is profound, this can often only be achieved through the deliberate or serendipitous participation of an external actor, since the condition itself precludes initiation of such goal-driven action. Such participation does not in and of itself constitute a mechanism of repair, but only creates a configuration which can in time lead to repair, particularly through revisitation. Repair is always an individual, autonomous occupation.
When revisitation of the subject of the sadness cannot possibly lead to satisfaction, because of a physical destruction (e.g. a death), revisitation is obviously ineffective. Goal structure can often be reconstructed, over time, but in very serious cases - invalidation of great regions of goal structure, or of its essential entirety - emotionally fruitful reconstruction may be impossible or nearly so, so that revisitation is imperative. Reconstruction is least feasible when invalidation of a significant goal invalidates most or all significant constituent goals - that is, results in a situation in which no rearrangement of significant goals produces a valid goal hierarchy. It is most feasible when the significant goals that are former constituents of a significant goal that has been invalidated, can themselves be arranged into a valid goal hierarchy or symbiotic confederation thereof. Invalidation of a goal of great significance, and in particular, of a goal at the apex of a major goal hierarchy, is effectively plasticizing. Goal topology enters a state of exaggerated fluidity, facilitating though not guaranteeing successful reconstruction. When an apex goal is invalidated in the context of a highly integrated goal structure, this plasticization is most dramatic, and an arbitrarily large volume of unsupportive, inefficient, or conflicting legacy goal structure is rapidly annihilated, as significant and still valid goal structure is promoted.
Goal structure reconstructive capacity varies dramatically on an individual basis, and as noted above, is a prime metric of fundamental corticostriatal aptitude. Rare individuals are capable of rapid and autonomous reorganization of goal structure in a manner that dispenses with an invalidated goal (particularly, a goal invalidated in a manner explicable purely on the basis of probabilistic logic), even an invalidated apex goal, emplacing a valid goal structure often composed largely or entirely of pre-existing goals, and often taking the form of a strategically powerful, closely allied confederation of a small set of goal hierarchies. This capacity relies to a substantial degree on all the other capacities enumerated as fundamental metrics of corticostriatal aptitude.
In many cases, the longer reconstruction is attempted in vain, and the longer revisitation is delayed, the more difficult is the actual restoration of goal structure enabled by revisitation. The difficulty arises because the attempts at reconstruction, while failing at constructing a viable (integrated) goal structure, succeed in further damaging the original, subjectively invalidated goal structure. A special case of external actor participation is falling in love which, in its most dramatic form, wipes out almost all non-phylogenetic goal structure, in an essential discontinuity of identity. A new top level goal structure is then constructed, based on environmental inputs, thoughts, and memories. Thus, falling in love, though it can lead to precisely the grave morbidities described above, can also resolve them - and particularly, can resolve them when no other method is effective and sufficient. Falling in love, it is vital to note, is accompanied by a certain degree of goal structure fusion, possibly including a transformation of sympathetic sadness into real sadness, as invalidated but unreconstructed goal structure is adopted.
Lachrymation and crying are social signals whereby others are informed that an individual's goal structure has sustained injury.
The phenomenon of falling in love is implemented at its core by the amygdala and projections thereof. Love itself is not meaningfully definable, as its intended denotation is sufficiently variable that the word is unusable without qualification. The most intense and robust emotional bond that occurs between actual or potential sex partners precipitates from the following process, and this bond is one definition of love.
Falling in love is a rearrangement of goal structure, which if freely embraced in its most intense form by consciousness places procreative partnership with the subject at the apex of corticostriatal goal structure, usually through association of preeminent significance with it and occasionally by construction of a completely integrated goal hierarchy capped by the apex goal. A subject is chosen based on the phylogenetic predispositions of the amygdala, modulated by several types of extra-amygdalar context. This context includes suitability of the individual to the demands of pursuing the apex goal (emotional and cognitive vigor) and suitability of the subject to the role of apex goal (a crucial factor proportional to which the intensity of amygdalar signalling is modulated). This perception of suitability is driven by phylogenetically dominated inputs from the narrowly defined sexual brain described above in section 3.4.5 (particularly the hypothalamus), and by pre-existing but partially unconscious corticostriatal goal structure. This goal structure is often adopted from society, but among those with high corticostriatal aptitude (as enumerated above in section 184.108.40.206), consists largely of personal inventions and principles based on introspection, fancy, and empirical (though subjective) grounding in natural physical principles. Additional vital measures of suitability is estimation that the subject has fallen or will fall in love with the individual, and the expectation that the individual will be capable of fending off challenger suitors. These estimations are largely unconscious and of evidently vast complexity.
The intensity of the amygdala's action is also modulated proportional to the difficulty perceived by the amygdala in achieving the apex goal. The amygdala does not distinguish between internal corticostriatal resistance (greatest among those with high corticostriatal aptitude) and the resistance of external obstacles, including those erected by the subject. The amygdala's psychotomimetic modulations (enumerated below) normally end either when it concludes that the apex goal has been installed with sufficient significance, or when it concludes that the apex goal has been and will continue to be fulfilled, and at any rate, wane with time and recur only sporadically and at an attenuated level.
The amygdala, through a prolonged upward modulation of the reinforcement signals diffused by VTA and n. accumbens, causes a plasticization of conscious goal structure, making goal annihilation and construction unusually easy, and inhibiting the normal tendency to reject inconsistent goals. The modulation of VTA plasticizes frontal cortex and the neostriatum directly, and participates in the modulation of the telencephalic nodes of the MCC. N. accumbens, through its projections to the telencephalic nodes of the MCC (particularly to the hippocampal region), is the linchpin of the mechanism whereby the MCC is modulated. Neurodynamically, the modulation of n. accumbens mimics schizophrenia (as described above in section 3.4.5), underscoring the importance of emotional and cognitive vigor in an individual who falls in love. In fact, the entire corticostriatal modelling engine is plasticized to a degree, directly implicating polymodal associative parietal cortex (Brodmann 5 and 7) and other regions. Nonetheless, corticostriatal regions embodying goal structure are plasticized to a far greater degree, since they alone are affected by both the accumbal and VTA reinforcement signals.
Once the amygdala perceives installation of the apex goal with sufficient significance, the accumbal and VTA modulations are released, and corticostriatal cognition in general and the memory coordination circuit in particular return to their usual dynamic. When conflicts and inconsistencies are detected, they are reconciled through invalidation of less significant goals.
The amygdala permanently imprints internal sensory signatures of the subject, and triggering on information drawn from afferent connections from associative cortex (both sensory and non-sensory), signals often intense pleasure whenever the subject is contemplated or encountered, to instill association between the subject and pleasure. This, more than any other process, creates a tendency for the amygdala's apex goal to be embodied with consistency and integration as the apex goal of the corticostriatal system.
The apex goal is also installed in the corticostriatal system by a process separate from the straightforward reward system just described, and this mechanism is particularly evident when the amygdala's action is intense - that is, when the individual is deeply in love. This mechanism probably consists of a set of mapped (structured) amygdalar signals that are interrelated with each other. One likely set projects to components of the MCC, and acts in a reinforcing role for projections to isocortex. One set of signals projects to frontal cortex, coercing it in some manner that precipitates rough installation of the apex goal. Another signal projects to parietal cortex, precipitating a breakdown of the identity boundary between the individual and the subject, particularly causing a fluctuation of subjective somatic identity (a sort of somatoform dissociation syndrome). The effect is to cause the individual to tend to value the welfare of the subject as he values his own, particularly in terms of biological integrity, but also in general terms of goal fulfillment (effectively, goal structure fusion). The amygdala's projections to temporal and insular cortex may also be used to operate directly on memory complexes and the poorly understood integrative complexes of insular cortex, likely in a manner supportive of the frontal and parietal projections.
A separate set of amygdalar projections to the neostriatum and possibly to frontal cortex coerce consciousness so that the apex goal is a continuous subjective presence. This phenomenon is a type of obsession. The continuous consciousness of the apex goal greatly increases the significance associated with it.
Arbitrarily large swathes of goal structure and world view inconsistent with the new apex goal and supporting world view are annihilated or deeply eroded in the above processes. The pleasure signalled by the amygdala works to counter the great pain which accompanies - and impedes - the destructive transformation of goal structure. The reality of the destruction is undeniable and often leads to subjectively incongruous sadness and crying.
The amygdala's systematically keyed reward signal, corticostriatal plasticization, and mapped coercive signals, are the keystones of the phenomenon. In combination, they cause a linkage of the apex goal to a vast array of goals and cognitive models that would otherwise be independent of the subject. This increases the significance of the apex goal, and facilitates adjustment of goals and models inconsistent with the apex goal. The amygdala does even more than this, though, in particular by signalling novel cravings, aversions (disgusts), and protections, in a manner supportive of the apex goal.
All these amygdalar signals constitute impositions of largely unamendable goal structure, world view, and attention. Because the amygdala is unconscious and autonomous, falling in love is perceived as an external imposition on conscious identity. Hence it is often perceived as an alien trauma, and determinedly opposed. Such opposition predictably leads to vastly inconsistent and disintegrated goal structure (fractured identity). Moreover, the premise that the amygdala's actions are an alien imposition is false. The amygdala's decision to fall in love is based in large part, and particularly among those with high corticostriatal aptitude, on corticostriatal models and goal structure - on conscious identity, and particularly, on its most significant components. Thus, falling in love is in large part an extension of conscious identity, and not an alien imposition. Nonetheless, some of the models and goals upon which the amygdala bases its decision may have been subjectively invalidated in whole or in part. In this case, the amygdala's influence runs counter to reconstructive efforts which may, themselves, be actual or potential successes or failures.
Hate is the emotional stance an individual has toward an animate subject (a conscious subject with goal structure) who actually or potentially reduces or annihilates the expectation that a significant goal will be fulfilled, and is proportional in intensity to the significance of the affected goal or goals, and to the degree of reduction in expectation that is experienced or expected. It is felt when the animate subject does not contribute positively to the expectation that some other significant goal will be fulfilled, or when this contribution is not consciously considered, or is considered to be relatively diminutive. Hate comes in three flavors. The first is accompanied predominantly by disgust, with an animate subject that potentially affects a significant goal, when this potentiality can be avoided by avoiding approach. The second is accompanied predominantly by anger, with a subject that potentially affects a significant goal, when this potentiality can be avoided with aggression. The third is also accompanied predominantly by anger, with a subject that has actually affected a significant goal, and the effect has not been reversed. A hate vanishes when the initial cause of the hate is subjectively reversed or absent, or when the affected goal or goals have been invalidated in a manner which does not involve the subject, or as a consequence of perception by the MCC of an overwhelming incongruity with reality.
Primitively, hate is (with the emotional coloration enumerated above) a goal to kill the subject (terminate the subject's capacity to maintain and pursue its goal structure), a goal which is nonetheless not usually actively pursued or fulfilled, as usually, existing goal structure would be injured or annihilated by this act. Typically, causation of injury to the goal structure of the subject, particularly by causation of emotions in the subject in a manner injurious to goal structure, or infliction of often minor and transient physical injury to the subject, substantially sates the goal to kill for a time. Clearly, inconsistency in goal structure can lead to paradoxical hate. The definitive such morbidity is self-hate, resulting from inconsistent goal structure which drives an individual to act in a manner injurious to significant goals. This hate can come in any of the three flavors. Also, the subject with whom an individual has fallen in love is in many (though certainly not most) cases also a subject of intermittent hate (in any flavor). This morbidity is particularly common among those with high corticostriatal aptitude (as enumerated above in section 220.127.116.11).
Shame is a sensation that accompanies subjective invalidation or erosion of a goal when the individual perceives that his actions caused the invalidation or erosion. Shame includes pain. Shame is proportional to the significance of the goal and to the prior expectation of its fulfillment. This expectation is particularly high when social examples of fulfillment exist. Guilt is shame involving a goal adopted consistent with a goal of another individual or group thereof. Such goals are social expectations. To a degree, guilt is the converse of sympathetic sadness. The cause of one individual's shame can be the cause of another individual's sympathetic sadness; there is no such thing as sympathetic shame.
Regret is a desire to change an action already taken by the individual, when that action resulted in the subjective invalidation or erosion of a goal. Regret is essentially a type of sadness: the desire (the goal) cannot be fulfilled and is thus spontaneously annihilated. This results in the pain that accompanies sadness. Regret and shame often co-activate, but either can appear without the other.
Embarrassment (when intense, humiliation) is the sensation that accompanies subjective recognition that one has acted or is acting in a manner inconsistent with or injurious to a goal. Embarrassment is proportional to the significance of the goal and the degree of inconsistency or injury. It includes pain. An action can itself be construction of a model or goal, so that embarrassment can follow from recognition that a model or goal is inconsistent with pre-existing models or goals considered to be valid. Embarrassment can be experienced sympathetically, but more interesting is the phenomenon of one individual experiencing embarrassment through extrapolated sympathy driven by recognition of another's inconsistency, even when the other individual has not himself made the recognition. Blushing is a social signal by which others are informed of an individual's errant action - that is, informed that an individual has acted in conflict with his goal structure.
Contentment, treated briefly, is not as it is generally advertised. Contentment is a condition of pleasure, absent pain, and absent desire (goal-directed behavior in general and craving in particular), and is thus a mental stasis within which corticostriatal activity in general, and consciousness in particular, are greatly attenuated, in the most extreme cases near the point of extinction. Contentment is a suspension of the mind. It can be precipitated by approach toward and fulfillment of goals, since this causes pleasure and also causes the extinction of the goals that are fulfilled. Though in short duration, contentment can - like sleep - be a vital rest period for the industrious, in longer durations it is a morbid prolongation of the pleasure that accompanies progress toward and attainment goals. Moreover, the mental indolence of contentment can be fostered through trickery and manipulation completely absent satisfaction of a pre-existing goal. The most obvious and corrosive such trickery involves euphoric drugs, particularly prolonged (habitual) use of cocaine, opiates, amphetamines, and cannabinoids (note that the first brain-derived substance found to bind to cannabinoid receptors was named "anandamide", a derivative of the Sanskrit word for internal contentment), and habitual trancing and induced irrational fixation, particularly in religions.
Pride is contentment due to the recognition of goal fulfillment or approach thereto.
Joy is the emotion that accompanies progress toward fulfillment of a goal, and particularly, is experienced immediately upon fulfillment of a goal, and is proportional to the significance of the goal and the rapidity and magnitude of progress. Its crucial emotional components are pleasure, desire (goal-directed behavior and craving), and excitement. It is transitory, accompanying actions. Contentment can be viewed as retrograde joy, in that it is not necessarily transitory, and can be driven by memories of joy or of causes for joy. Both contentment and joy can be experienced sympathetically. Joy and contentment constitute the two flavors of happiness. The crying that sometimes accompanies intense joy is likely due to the effective goal invalidation that results from the fulfillment of certain types of goals.
Amusement is a mechanism with an emotional component, whereby the corticostriatal system identifies a stimulus as being, referring to, or reminiscent of something inconsistent with a cognitive model considered to be valid, and dismisses the threat of the stimulus, reaffirming the subjective validity of the model. Amusement, then, is a self-defense mechanism by which an individual preserves his model of reality, possibly contrary to reason, though it also acts in a social role, sometimes with no defensive aspect at all. Amusement is activated only when the indicated and dismissed alteration to a cognitive model would erode or annihilate a component of goal structure (virtually all models have this characteristic, of course), and the intensity of amusement is proportional to the significance of the affected goal. Since goal structure invalidation is painful in proportion to the significance of the affected goals, amusement is automatically incentivized through negative reinforcement of the alternative, in proportion to the significance of the goals affected by the challenged model.
Amusement is accompanied by pleasure, and thus has a positive incentive. Amusement usually precipitates smiling (in response to mild amusement) or laughter (in response to intense amusement), which, in combination with direction of gaze, are complex, nuanced social signals with highly context-dependent import for other individuals. Smiling is phylogenetically derived from the fear expression, and its activation by amusement is likely due to the perception of a threat to goal structure. In addition to simple communication, laughter plays the role of tending to halt the train of thought of the individual who prompted the laughter, through facial and vocal hyperbole (as observed by Marvin Minsky). The pleasurable and social aspects of amusement make it a major mechanism whereby communities propagate and verify consensus on matters of social import (which, in the final analysis, includes all matters). Of all emotions, amusement is the one most often and readily experienced through sympathy.
The commonality of smiling and laughter to joy, contentment, and amusement, is clearly indicative of an internal commonality. Amusement is an expression of acceptance of one's models and goals - of confidence in their validity. Joy accompanies events that constitute evidence that one's models and goals are valid. Contentment is due to the memory of such evidence, and similarly indicates subjective model and goal validity. Thus, the internal commonality which accounts for the external commonality is that all three emotions are the product of confidence in one's identity. Smiling and laughter are social signals that inform others of an individual's confidence in his identity, a confidence which may nonetheless be misplaced.
The thalamus consists of two functionally separable and anatomically contiguous nuclear supergroups. The medial dorsal anterior ("MDAT") nuclei, composed of the (anomolous) mediodorsal nucleus, (anomolous) intralaminar group, lateral group, anterior group, and (anomolous) midline nuclei, comprise the integrative and telencephalically-oriented portion of the thalamus. The lateral ventral posterior ("LVPT") supergroup is composed of the ventral mass (though the ventral anterior nucleus is anomolous, more naturally belongs in the MDAT, and borders the anterior nuclear group and reticular nucleus), geniculate bodies, (anomolous) pulvinar, posterior complex, and the (anomolous) reticular nucleus.
Nuclei in the MDAT supergroup connect only with associative regions of the telencephalon, and except for the noted anomolies, are not intimately related with any rhombencephalic structures or pathways. All the nuclei of the LVPT supergroup except the reticular nucleus are intimately related to rhombencephalic structures, and all except the noted anomolies are linked only with primary and paraprimary regions and organs.
The intralaminar and midline nuclei are anomolous in that, like the ventral anterior nucleus, they link with the brainstem reticular formation. The mediodorsal nucleus is anomolous in that, like the ventral anterior nucleus, it is innervated by the substantia nigra. These rhombencephalic relationships within the MDAT are exclusively with the most associative nuclei of the rhombencephalon. The locus ceruleus and raphe may actually innervate nearly all of the MDAT, so that linkage with the excitement centers of the brainstem are not, in fact, anomolous at all.
The reticular nucleus reciprocates with most, or all, thalamic nuclei, and receives topographically organized projections from much of the cortex, though it has no extrathalamic efferent projections. Its role is unique, and by no means fully understood. The pulvinar, as explained above, has intimate links with both associative cortex and associative rhombencephalic structures, and can be considered a transitional nucleus functionally midway between the role of the MDAT and that of the LVPT. It is also the only globular thalamic nucleus which substantially straddles the mediodorsal-lateroventral boundary.
Much has been written about the striking organization of the reticular thalamic nucleus (nRt). Carpenter sums up neatly: "The reticular nucleus is situated so as to sample neural activity passing between the cerebral cortex and nuclei of the dorsal thalamus, but it has no projection to the cerebral cortex. Cortical projections to portions of the reticular nucleus arise from the entire cerebral cortex and are topographically organized. Since the major projections of the thalamic reticular nucleus are to specific and nonspecific thalamic nuclei, it probably serves to integrate and 'gate' activities of thalamic neurons."
The output of the nRt is inhibitory, and the output of a particular region projects back to the globular nucleus from which that region receives input. Furthermore, these regions receive input from the region of cortex to which the corresponding globular thalamic nucleus projects.
Neurons within the nRt exhibit extensive connectivity over relatively long ranges within the nRt, so that the inhibitory output of the nRt to a particular globular nucleus can be modulated in part by input from other, non-isomorphic regions of cortex and globular thalamic nuclei. Considering the breadth of domains covered by the full spectrum of globular thalamic nuclei, the position and arrangement of the reticular nucleus would seem to make it very important to the operation of the brain as a whole.
The proposal tossed about, and supported here, is that the nRt serves to focus and raise the contrast of the wavetrains passing through the thalamus, in a broadly integrated fashion. Since the nRt has purely inhibitory output, it is unlikely that it conveys information directly from one modality to another; it only carries information incidentally in the form of dampening. In this way, the nRt modulates wavetrains in such a way that it greatly influences which wavetrains have the strength and synchrony to amalgamate with the conscious wavetrain. This makes it essentially a global attentional spotlight, albeit a somewhat unclever one. It would be very interesting if it were discovered that the nRt is sensitive to harmonic and phase relationships between the wavetrains it samples.
There are many circuits that run both directions; without further examination of the particulars of projection fields and intranuclear linkages, the implications of this bidirectionality are unclear. Perhaps wavetrains circulating in both directions along homologous circuits result in something akin to a standing wave, with associated crests and troughs. The standing wave, when present, is inferred by neurons whose dendrites receive input from neurons implementing circulation and from those implementing countercirculation. Such an arrangement is not precluded by known basic cellular neurophysiology.
It seems clear that some circuits bifurcate and recombine in a single circulation. By this process, one portion of the wavetrain may exhibit processing (minimally, an advance or delay), and the components are subsequently recombined. The final effect is one of filtration, a primitive and generic form of pattern recognition. This type of bifurcation and recombination is particularly evident in the conscious circuits.
Circulation which is tightly localized, usually referred to as reverberation, is probably the mechanism by which modules (of the neurophysiological variety) internally maintain working state - myeloarchitectural plasticity cannot play a role in the maintenance of working state on the time scale of seconds. By this mechanism waylayed or otherwise latent information can serve to modulate the transformational function of the module when and if the module is made to form a portion of a circuit. Once it forms part of a circuit, the information is shuttled on internuclear and interregional trajectories, and by virtue of myeloarchitectural plasticity, is rendered permanent to a degree proportionate to the subjective significance of the information. Here, subjective significance is to be taken to be synonymous with resulting in wavetrains which are efficient at catalyzing changes in myeloarchitecture. This significance will often be dramatically modulated by the emotive circuits.
The modules and intramodular circuits just described, and Donald Hebb's cell assemblies and local reverberations, are one and the same. This organization is predominant in cortex, and may be similarly predominant in the neostriatum (based on sketchy cytoarchitectural evidence). This type of modularization is probably not relevant to the physiology of the thalamus.
The full variety of all the thousands of endogenous circuits, which at a given time may or may not have a wavetrain flittering through and evolving (if the circuit is circulational), implement those basic aspects of mind (tools and influences) that can be called upon by the conscious wavetrain when it has a job for them, or whose wavetrains join with the conscious wavetrain preemptively, thereby interrupting it, to provide input considered important or advantageous (though perhaps not by the conscious wavetrain).
Subconscious abstract symbolic cogitation involves circuits many of which do not even descend below the cortex. Circuits involving the hypothalamus, amygdala, and associative cortices, are responsible for a variety of nagging emotional and metabolic drive phenomena.
Beyond the thousands of endogenous circuits, innumerable circuits can be learned by dint of the plasticity of the cerebral cortex and of many higher brain nuclei. These circuits are very individual, and embody the full richness and variety of the human tapestry of mind. Many segments of these learned circuits are portions of broader circuit segments. I propose that it is through the delineation of innumerable fine-grained circuits that the endogenous course-grained circuits come to be arranged in a semantically powerful manner.
Wavetrain amalgamation is achieved through mediation at specific points of the circuits through which the wavetrains course. These are points where the two circuits have interleaved projection fields. Neurons (with associated axonic and dendritic processes) link adjacent patches of the projection fields, in a unidirectional or (usually) reciprocal fashion, and at a given time the states of these neurons and their processes embody a particular degree of association or dissociation between the two circuits. These neurons are sensitive to the signals coursing through the two circuits (in particular, they are sensitive to spatial, harmonic, and phase registration between them), such that the signals can bring about a change in the state of these associating neurons, thereby changing the circuit topology and further amalgamating or further dissociating the two wavetrains. Associating neurons and their processes form a neurodynamic bridge, and the high level interpretation of this bridge is that it serves to bear information between the two wavetrains.
Critical aspects of the neurodynamics underpinning many of my proposals are incompletely justified in this paper, though further justification does exist in other literature. Future research will be directed specifically at determining if, and precisely how, the physiological substrate is arranged so that wavetrains appropriately amalgamate and dissociate. This is, at present, the weakest link in the chain of reasoning detailed in this paper.
Much greater detail is needed in the delineation of projections and projection fields, and the functions of these projections and of the many subcortical nuclei (particularly in the thalamus and basal forebrain). This will involve laboratory work. My invocation of the term "wavetrain" throughout this paper leads to an impression of something approximate in time and space; such a smearing is often not the case with consciousness and with other processes of mind, and the particulars of projections, projection fields, and intranuclear linkages, must reveal how these wavetrains attain a tight spatiotemporal focus. Short of such a demonstration, the concept of the circulating wavetrain is incapable of fully accounting for the empirical phenomena of mind and behavior.
The Circulating Wavetrain theory promises to catalyze solution of many outstanding problems in psychology. It will help in the search for coherent explanations for symptomatic constellations of psychiatric and organic syndromes, and will presumably be helpful in deriving treatment strategies that aim to render the patient healthy, creative, productive, and therefore happy.
The theory offers a compelling explanation for the effect music (particularly, hypnotic and rhythmically regular music) has on the mind. I feel this is a good litmus test for any theory which purports to account for the subjective conscious experience.
My theory is compatible with (in fact, implicitly subsumes) the Hebbian theory of learning, which is itself a satisfying explanation for how learning is implemented at the level of neurophysiological substrate.
Donald Hebb's learning rule and theories of Cell-Assemblies and neural reverberations, Gerald Edelman's Neural Darwinism, and some of the precepts of the PDP school, are precursors of the Circulating Wavetrain theory.
A paper by Daniel Amit entitled "The Hebbian Paradigm Reintegrated: Local Reverberations as Internal Representations" electronically preprinted in 1994 and published in 1995 was a very concrete source of inspiration.
For a compelling discussion of the integration of some of the most important regions of isocortex, see "Brain Evolution and Neurolinguistic Preconditions" by Wendy K. Wilkins and Jennie Wakefield.
Speculative writings by William Calvin, Francis Crick, and others, seem to lead directly to the Circulating Wavetrain theory.
Marvin Minsky's Society of Mind model is one I recognized early as a powerful high-level interpretation of mental organization. The wavetrain model can neatly serve as an underlying implementation of SOM, though SOM does not account for consciousness.
A vast corpus of wrong theories of consciousness has been as instrumental in forming my theory as have the theories, most of which are of lesser scope, which I believe are essentially correct.
In my insistent quest to grapple with the brain on its own terms, Malcolm Carpenter's Core Text of Neuroanatomy has been a constant companion. His text, a joltingly dense book, has been the primary source of my understanding of nuclear modularization, internuclear linkages and their chemistries, and intranuclear cytoarchitecture.
Walter J. Freeman's MCB61 lecture outline (from UC Berkeley) inspired my theory of the neurophysiological correlate of falling in love (section 18.104.22.168). He proposes that a generalized mechanism of unlearning underlies socialization and pair bonding. In a telling summary of chapter 6, "Learning and Unlearning," of his book _Societies of Brains: A Study in the Neuroscience of Love and Hate_, he says:
"I describe learning, by which intentional structures stretch forth and change themselves through self-organizing, chaotic dynamics. I infer that neurohumoral mechanisms exist in mammals for unlearning by a meltdown of intentional beliefs without loss of procedural and declarative memories, which enables understanding between self-organizing brains by cooperative actions. We experience this as falling in love."
Steve Harnad's Psycoloquy mailing list has been effective in peppering me over the years with useful information and pointers.
Benoit Mandelbrot's "The Fractal Geometry of Nature," James Gleick's "Chaos" and Murray Gell-Man's "The Quark and the Jaguar" are three books oriented toward a more general audience that have set various ideas running in my head as I was introduced to them at intervals over the last fifteen years.
Innumerable sources, some anonymous, have shown up in my Altavista searches for more specific information on particular topics.
(This glossary is out of date -DP 2000-May-5)
Multidimensional wavetrain --- a signal which is not scalar. A prototype of such a signal is a train, or sequence, of matrices (a train of tensors). However, such a train is quantized in a way quite dissimilar from the quantization of the multidimensional wavetrains which circulate through circuits in the brain. The multidimensional wavetrain is not an exotic concept; examples of multidimensional wavetrains are optical and sonic wavetrains in three-space; motion holography and true sonic holography (a dense 3-D matrix of computer-controlled loudspeakers) both generate artificial multidimensional wavetrains.
Population --- a contiguous set of cells of like architecture and chemistry.
Nucleus --- a contiguous agglomeration of one or more distinct populations, usually bounded by non-nuclear matter of some sort.
Projection --- a set of fibers that convey information from one population to another. A projection may bifurcate at some point along its trajectory and give off "collaterals" so that more than one population is targetted. A projection is characterized by its length, its myelination, its propagational velocity, and its chemistry (these four dimensions are not orthogonal). The fibers that compose most projections involve a synapse at some point along their trajectories.
Projection field --- a precise pattern of fiber projection; it is particularly characterized by the mapping function by which a trajectory can be derived from a particular source neuron, and by the projection fields with which it is interleaved at the target.
Cortex --- a laminar arrangement of distinct population shells encasing a non-laminar nuclear body or fiber mass.
Module (neurophysiological) --- a small region of a nucleus or cortex whose boundary is characterized by a marked falloff in projections to and from adjacent neurons. Modules in cortex interrelate the different types of neurons in the several layers of a given area of vertically registered cortex, layers which are composed of architecturally distinct types of neurons (and therefore comprise multiple populations with a disciplined interrelation).
Medulla --- phylogenetically oldest, anatomically most basal, and computationally most primitive, portion of the brain.
Rhombencephalic --- phylogenetically derived from the medulla.
Cerebellum --- a vastly intricate rhombencephalic organ, comprising roughly half the neurons of the central nervous system. It is responsible for refinement and embellishment of the motor instruction stream, freeing the conscious portions of the brain from computationally expensive and time-consuming chores.
Cerebral cortex --- the external surface of the upper brain, really wrinkly and quite gigantic in humans.
Isocortex --- the portion of the cerebral cortex (often called just "cortex") that has a more or less continuous and unexceptional layered arrangement and manner of connection to internal brain structures and other regions of cortex (6 principal layers are constantly detectable).
Heterocortex --- oddball parts of the cerebral cortex whose physical arrangement is strange in one or more ways. Isocortex and heterocortex are continuous, and the traversal of a boundary from isocortex to heterocortex involves reorganization or partial collapse of laminations.
Domain-specific --- a population or cortical area dedicated to operation at the level of an external domain (a sense or motor field) - almost always arranged with a straightforward mapping between the key attribute of the domain and the topographical location in the population of the several neurons associated with that specific range in the domain. Examples are auditory cortex and associated subcortical nuclei (cells positioned based on frequency at which they turn on), visual cortex and associated nuclei, somesthetic cortex and nuclei, and somatomotor cortex and nuclei. Olfaction doesn't have this kind of organization (there no a priori map supplied by the environment), but that's just one of the many very strange and exceptional aspects of olfaction.
Primary cortex --- domain-specific cortex
Associative --- a population that is associated with more than one external domain, or is connected to only such populations. By this narrow definition, many regions classically considered to be associative (particularly paraprimary cortex) are seen to be integrative within one domain, but not associative (synonymously, not polymodally integrative).
Paraprimary cortex --- region of cortex adjacent to a primary region. Paraprimary regions are domain-specific, though there is a definite integrative aspect to their operation.
Relay nucleus --- a simplistic nucleus that sends a signal on down the line with little if any transformation of the signal. Such nuclei often receive fiber bundles on multiple trajactories, and project an output amounting to a reorganization and regrouping of these fiber bundles, also often with multiple trajectories.
Reticular formation --- a nuclear complex with involved intranuclear and intracomplex connections - compare with relay nuclei.
Raphe nuclei --- a variety of nuclei distributed throughout the central grey column of the brainstem, which form the most important portion of the brainstem reticular formation.
Habenular nuclei --- a pair of diencephalic nuclei that serve as a nexus through which telencephalic signals are relayed to brain stem nuclei, and thence on to (largely autonomic) general visceral efferents.
Thalamus --- an agglomeration of many (25) nuclei positioned just above the brain stem. At least one nucleus of the thalamus connects to every little piece of the whole isocortex. The thalamus has domain-specific nuclei devoted to each of the major sensory domains (except olfaction), a set of motor relay nuclei, and a variety of (far more interesting!) associative nuclei which are connected both to the associative regions of the telencephalon and to other thalamic nuclei.
Diencephalic --- phylogenetically derived from the thalamus.
Hypothalamus --- a set of 15 nuclei that deal with metabolic and reproductive drives and the hormonal aspects of emotion. Hunger, thirst, metabolism and thermal regulation, and secondary sex characteristics are star attractions here, though there are smaller players. The mammillary bodies are among these 15 nuclei.
Amygdala --- a set of 9 nuclei that define and assert middle-tier emotional state, specifically fear, aggression, and probably desire and attachment, but definitely at least some other recognizable and named emotions. Some of these nuclei also exert a direct effect on visceral and vascular state ("so scared he peed in his pants").
Septal nuclei --- a pair of telencephalic nuclei which serve as major relay points for signals from the amygdala and hippocampus to the hypothalamus, back to the hippocampus, and to more basal nuclei including (through the habenular nuclei) the brain stem.
Corpus striatum --- a set of very large nuclei (inches long) with chemically distinct populations organized in a patchy matrix. includes the putamen, caudate nucleus, globus pallidus, and amygdala.
Basal ganglia --- a vast nuclear supergroup composed of the corpus striatum, septal nuclei, ventral striatum (olfactory nuclei), and nucleus basalis.
Telencephalic --- phylogenetically derived from the basal ganglia. The cerebral cortex is telencephalic.
Caudate nucleus --- a surprisingly long arc-shaped nucleus, forming the superior portion of the corpus striatum. The caudate nucleus is the primary site of initiation of action (site of high-level intention). The caudate is continous with the amygdala at one end and the putamen at the other.
Putamen --- the inferior (more basal) portion of the corpus striatum. The putamen is somewhat more wrapped up in the middle-level actualities (motor logistics) of intentionality, but still plays an integral role in the high-level initiation of action. This delineation of functionality between caudate and putamen is overly speculative and should be taken with a 50 pound bag of salt.
Orbitofrontal cortex --- the portions of the cortex, including prefrontal and posterofrontal, that deal with hierarchical and temporal (time) modelling, and half of the mechanism of forward and reverse kinematics. This area is highly associative. The frontmost area of orbitofrontal is called prefrontal and is crucial in modelling the world as a continuous, causal place (and making predictions on that basis). A region known as Broca's Area is in the lateral inferior frontal lobe. This area is where the grammatical, parsing, and reverse-parsing (construction of a sequence of actions, either written letters or spoken syllables) aspects of language are implemented (not as such, this hardware is usurped for the purpose of language processing (often in the left hemisphere, always in only one hemisphere) because it happens to be suited for it).
Non-auditory temporal cortex --- oriented toward declarative memory, for what it's worth. This is probably the closest to a region that implements what is classically called "memory." It is rich in associations, serving as a metarepository by having innumerable little regions distinguished by the particular sites in other cortical regions to which they connect. Zap one of these regions with a few millivolts and you can cause conscious experience of a whole, intact memory. The stimulation artificially declares a state, activating the polymodal constellation of a memory, and (through the rich linkages with nodes of the conscious and MCC) bringing this constellation into consciousness. Wernicke's Area is in this region. This is the area concerned with the semantic aspect of language. Wernicke's Area and Broca's Area are intimately related and connected by a huge bundle of fibers. Between the two of them, they are responsible for the comprehension and production of language. Only one side of the head uses these regions for language; their twins on the opposite side are used for spatial processing and, well, "right brain stuff" (language is confined to one hemisphere, usually the left) - no one quite knows everything that can be done with this hardware when it's not used up by the needs of language processing, but Albert Einstein is a good example of someone who pushed that envelope. Never let it be said that science is a left-brain activity!
Lateral and posterior parietal --- region implementing the other half of forward and reverse kinematics. This region is responsible for "body sense." When one figures out the shape and identity of an object by touch alone, this region is primarily responsible for identifying features and producing (and projecting) a signal which can be integrated with other representations, particularly visual and procedural ones. That's why a brick feels like a red construction material. The precise area that a signal like this projects to is the junction of the temporal, visual, and parietal regions, called the POT (parietal-occipital-temporal; visual is confusingly called occipital in most literature) and also called Wernicke's Area. This is the most associative region of the entire sensory cortex - it is fed by regions which are themselves already associative. The POT exists only in humans - in fact, it exists only in "homo" humans; australopithecus afarensis apparently lacked the POT but homo erectus had it - now there's food for thought. It is reasonable to hold that presence of a POT is a necessary and sufficient indicator for being human.
Lateral anterior visual cortex --- a highly integrative, and perhaps associative, area responsible for visual modelling. The portion of the cortex devoted to vision alone is quite massive; we have a large biological investment in visual thought and this investment is evidenced by our culture and behavior (and vice-versa).
Regions of isocortex not included in this glossary --- domain-specific regions for each of the sense and motor modalities except for olfaction, which is heterocortex (strange!).
Cingulate gyrus --- region of heterocortex which mediates recruitment of memories. Because of its inclusion in some very important emotional circuits, I propose that the cingulate gyrus is key for the automated recruitment and unintentioned incorporation into consciousness of memories relating to current circumstances - cingulate and the caudate nucleus are probably the key to understanding and alleviating post-traumatic-stress disorder (whose most devastating symptoms are hypothalamic and amygdalar in nature, but quite probably not autonomously caused by these subcortical nuclear complexes).
Hippocampal formation --- crucial component of the MCC, which converts short-term memory to long-term memory (see text). it perhaps plays a non-critical roll in the recall of these memories (placing them into short-term memory registers). The subiculum, dentate gyrus, and hippocampus proper, are all part of this formation, though the dentate is often not included for reasons unapparent to this writer.