The purpose of this series has been to try to identify the neurological structures within which mind/identity/self exists for the purpose of ensuring that biostasis does not irreparably destroy those structures. Since this could be a matter of life or death, I have sought to maintain my focus on neuroscientific fact and to limit speculation. Nonetheless, the time for speculation has come. Sheer factual data by itself does not yield insight, but factual data can strengthen speculation leading to better factual data and insight. Neuroscience cannot, at present, tell us the anatomical basis of mind with certainty, but it gives a great many clues.

I have previously identified various locations in the brain which seem to be specialized for various kinds of information processing. I have not specifically identified a "center of consciousness" and, in fact, have implied that there is no such center. In my discussion of the visual cortex, I referred to the specialization of the V4 region for color, the V5 region for motion, the V3 region for orientation and the V6 region for depth perception. I also mentioned that there is no one location in the brain to which all of these regions "report". Specifically, there is no "little person" in some small area of the brain who puts together the color, motion, orientation and depth information to "see" the image. This "little person" is technically known as a homunculus and this model of how the brain works is known as "the fallacy of the homunculus". If we imagine a tiny center in our brains (a little person) who sees the information coming from our eyes, hears the information coming from our ears, smells the information coming from our nostrils, etc., we are begging the question of how the brain works. We are also left with a silly infinite regression of homunculi, since each homunculus would need a tiny homunculus in his or her head.

A bee colony is more than just a collection of bees, and a brain is more than just a collection of neurons. It seems mysterious that a mind could be distributed and only exist through the operation of billions of neurons. Some neurons have specialized operations (like queen bees and drones), but the analogy breaks-down when you begin to talk about the localized functioning of collections of neurons in nuclei and regions of the cerebral cortex. Visual perception does have some hierarchical character insofar as the recognition of visual objects takes place in the temporal lobe. The majority of these temporal lobe neurons participate in facial recognition. (Inputs to the temporal lobe are primarily from V4 because V4 is specialized for form & stereopsis as well as for color — essential features for object recognition.) The determination of location in space takes place in the parietal lobe of the cortex. But specialization of function does not necessarily mean hierarchy. Destroy the V5 region and the subject will see life as a series of still pictures — motion is absent although recognition can still occur. The full experience of a recognized object in motion in a general location requires the activation of neurons in all the relevant centers (and the flow of information is bidirectional in every case).

Immediate (scratch-pad) memory is active in the working-memory areas of the frontal lobes. Recent memory is processed by the hippocampus. Long-term memory for information (such as the date of your birthday) is likely stored in the parietal lobe, whereas long-term memories of events in your life (such as a birthday party) is likely to be stored in the temporal lobe. Recalling a memory, however, will also activate the frontal lobe.

Nonetheless, memory in the brain does not function like memory in a computer. Recalling the image of a banana does not simply mean retrieving an item from disk (temporal or parietal) into active RAM (frontal lobe active memory). In the brain, recalling a memory means activation of neurons at the sites of memory storage. (Sites is plural, because memory storage is undoubtedly coded as synaptic strengths for many synapses distributed among many neurons.) A person with a lesion in the V4 (color) area who does not see colors fails to see color in memory. A remembered banana will be "remembered" as gray, even if the memory of the banana was formed prior to the lesion. The search for the engram (single memory storage site) probably failed because there is no engram — memory is distributed, not localized.

Our identity, our active consciousness, is not simply the sum of our memories. The vast majority of our memories are lying latent in our minds most of the time. While we are remembering that we must renew our driver's license, we are not remembering the name of the capitol of France, or the number of planets in the solar system or meaning of the word "holography". Memory must be organized in such a way that we can know what we know and have a way of retrieving the memories we want, when we want them.

The phenomenon of attention seems central to a notion localizing consciousness in the brain. When we pay attention to a thought, a sound, an itching toe, a memory, etc. our consciousness seems to willfully concentrate on a few amongst many possible inputs. What we experience is not simply what our environment subjects us to, but what we pay attention to in our environment. At a social gathering where many conversations are in progress simultaneously, we can follow one conversation and "tune out" all the others by an act of will. Nonetheless, if our name is spoken in one of the "tuned-out" conversations, our attention may suddenly shift even to a conversation which we thought was outside our awareness.

The most global control of attention apparently comes from the prefrontal cortex. Distractibility is often observed in animals with prefrontal lesions. The prefrontal cortex sends inputs to the reticular nucleus of the thalamus, which is able to gate transmission from the thalamus to the rest of the cortex. Finer control of attention in peripheral discrimination requires involvement of the pulvinar nucleus of the thalamus.

We concentrate attention on each action required for driving a car until mastery of the actions allows them to be performed without much attention. A child learning to read must concentrate on how letters form words. A mature reader pays attention not to the reading process, but to the meanings the reading conveys — and to the thoughts those meanings stimulate. Attention is like a mental magnifying glass which we hold up to our experience. How do we do it?

About one-quarter of the cerebral cortex in humans is dedicated to processing visual information. Attention, especially to visual objects in space, is best done by the right hemisphere. So-called "unilateral neglect", wherein a patient seems to lose awareness of half of his/her perceptual hemisphere, is most frequent & severe after lesions to the right hemisphere. Visual attention need not be at the center of the visual field. For example, young monkeys rarely look at a dominant male because eye contact is a threatening gesture, but the dominant male is nonetheless a focus of attention.

PET scans of a brain performing an attention-requiring task give a good idea of which brain areas are functionally active. In one such task, a subject may be flashed one of the 3 sequences 585858S585858, 5858588585858 or 5858585585858 — and asked to identify whether the center letter is a "5", an "8" or an "S". A series of such flashes occurs, so the subject knows the approximate expected location of the sequence. Recognition of the target letter requires much attention because of the similarity of "detractor" letters to the target letter, and because of the closeness of the detractors to the target letter.

A PET scan not only shows the expected activity in the visual cortex, Inferior Temporal (IT) cortex and Posterior Parietal Cortex (PPC), but also shows activity in the DorsoLateral PreFrontal Cortex (DLPFC) and the VentroLateral PreFrontal Cortex (VLPFC). The activity of the DLPFC reflects working memory expectation of the location of the target letter. The activity of the VLPFC represents working memory expectation of the target letter shape to be recognized. These working memory areas are in close communication with the PPC and IT, respectively.

The pulvinar is the largest nucleus in the thalamus, occupying two-fifths of the thalamic volume. The pulvinar plays a crucial role in attention, by contributing to the activation of neurons for the object which is at the center of visual attention, and by contributing to the deactivation of other neurons, especially those corresponding to the visual field of the detractor letters. Although the pulvinar might seem to be controlling attention, it is not much more in control than a light-switch is in control of whether a light comes on. A more complete picture would include the anterior cingulate gyrus (which conjoins motivation with physical action) and the superior colliculus of the tectum (which controls eye movement). As the PET scan shows, the experience of attention correlates with neuron activity in all of the areas illustrated.

Attention allows us to increase the speed, accuracy and efficiency of our actions. By attending to a stoplight, we can more rapidly respond when the light turns green. My assessment of the way this occurs would be to say that working memory and the pulvinar activate neurons for the recognition of the green stoplight (IT) and the location of the stoplight (PPC) so that less additional activation is required when the light actually does turn green. In the case of waiting for a stoplight, attention is also directed to the footpedal so that the subject can rapidly step on the gas. The pulvinar serves a "gating" function — directing which neurons responding to our sensory experience are to be most activated. But this does not make the pulvinar the center of our consciousness. We are most conscious of what we are attending-to.

We can direct our attention to ruminate upon a memory or to recognize an object or to solve a problem. PET scans, monitoring individual neurons show that the conscious experience is unquestionably associated with the activation of neurons. A person who is unconscious has no active memories and (if unconscious enough) no activated (depolarizing) neurons. Yet regaining consciousness, memories can again be recalled. Memory may be essential for consciousness, but it is not identical with consciousness.

Similarly, the Reticular Activating System (RAS) in the upper pons is essential for arousal and consciousness, but the RAS is not identical with consciousness, nor is it the center of consciousness. The RAS is itself subject to control by exterior stimuli — and is even subject to inputs from the cerebral cortex through a "bootstrapping" process whereby the awakening cortex sends more signals to the RAS. The cortex requires the RAS for arousal much as the cortex requires the heart for blood — but the heart is not a center of consciousness.

Memories — passively stored synaptic connection strengths — influence patterns of activated neurons in the cerebral cortex. But patterns of activated neurons represent consciousness, not passive synaptic connections strengths. If it is not the ultimate mystery of consciousness, it is nonetheless somewhat astounding and incomprehensible that patterns of activated neurons represent a consciousness. How does this result in unity of mind? How does it represent mind at all?

The prefrontal cortex, particularly the dorsolateral cortex, contains much of the functionality often associated with the word "consciousness". Patients with frontal lobe lesions have difficulty making estimates or inferences, such as estimating prices, weights, etc. In association with working memory is the capacity to imagine the consequences of hypothetical actions or events. This kind of "if-then" reasoning or simulation is a crucial part of planning for action — although the orbitofrontal cortex is probably required for a decision and the anterior cingulate cortex probably generates emotional states based on reward expectancy to help put a plan into action though influence on executive centers.

If PET or MRI scans are an indication of consciousness — if neuron depolarizations are the essence of consciousness — then there is no one center of consciousness in the brain. Rather, consciousness shifts from brain region to brain region — in the parietal lobe when doing a calculation, in the temporal lobe when trying to "place a face", and in the frontal lobe when trying to decide whether to carry an umbrella. It would be a mistake, however, to equate PET or MRI scan activity with consciousness. The cerebellum may be very active in calculating the anticipated expected position of a rapidly-moving limb, but it seems likely that only the results of cerebellar activity enter consciousness. Is the cerebellum simply a co-processor of the brain which does not participate in the essence of consciousness? Can the same be said of the pulvinar, which may "gate" attention but, being subject to outside influence, neither controls consciousness nor is included in consciousness. Is consciousness only an attribute of the cerebral cortex? Is hunger experienced in the hypothalamus or in the cortical regions with which the hypothalamus communicates? (Cats with no cerebral cortex are able to feed and function, though with far less evidence of "consciousness".) Consciousness may well be the sum of several cortical and subcortical regions acting in conjunction. Moreover, it seems unlikely that we are aware of all cortical activity since V1 in the visual cortex, for example, seems to be more of a pre-processing area than an area participating in conscious awareness.

Motivation needn't be conscious. Sigmund Freud was fond of finding hidden "unconscious" motives for seemingly accidental mental events. The idea that painful experiences can be repressed from conscious memory was an important part of the "theory of the unconscious mind". It may be that consciousness is only the tip of the iceberg of mental activity. But it seems more likely that co-processors, rather than a hidden mental manipulator, are primarily what is "behind the scenes" of consciousness. The nuclei of the thalamus have distinctive (usually reciprocal) connections with different areas of the cortex. The basal ganglia are strongly connected to the frontal lobes, and their participation in cognitive functions make them prime candidates for sub-cortical participation in consciousness.

The hypothalamus is the source of many of the most elemental emotions: hunger, thirst, chills, etc. — ultimately pleasure & pain. Painful stimulation of a limb can lead to the withdrawal reflex, mediated directly in the spinal cord. Pain receptors from the skin & organs project directly to the somatosensory cortex, although many of these ascending fibres terminate in the reticular formation (increasing arousal) and the periaqueductal gray. Yet all these sub-cortical drives can often be over-ridden by higher centers of motivation in the cerebral cortex. A person on a hunger strike can resist eating even to the point of death.

The anterior cingulate gyrus (Brodmann Area 24) is that part of the cortex (and limbic system) often mentioned as the ultimate locus of motivation control. Francis Crick, in THE ASTONISHING HYPOTHESIS, speculates that the anterior cingulate gyrus is the seat of the will. Sitting adjacent to the motor cortex it seems well-situated for this role — and it is well-connected with the frontal cortex and with the rest of the limbic system.

A motive need not result in action. A person may want to buy a new car, but refrain from purchase because of the expense. An ex-alcoholic may want to drink alcohol, but resist doings so out of fear of the consequences. Do such conflicts exist in a single motivation-center, or are there different centers in the brain for different types of motivation? If the latter, is there a single center for conflict-resolution? It seems likely that, just as consciousness can apparently migrate from place to place in the brain, motivation can arise from different parts of the brain at different times. A "competition" may exist for ultimate control of the will, rather than an ultimate arbiter, and the baton may pass from hand to hand (brain area to brain area) like a "token ring" in a Local Area Network (LAN) of Personal Computers (PCs).

Pain can be described as a signal directly from the body to the cerebral cortex, which warns of injurious environmental conditions. Fear has also been described as a warning signal, which comes from the body to the cortex — but the environmental stimulus usually first enters through the eyes and ears. Thus, a threatening condition appears in the environment, the cortex becomes aware of the condition, signals are sent from the cortex to subcortical structures & body organs, and then the cortex receives "fear" signals back from the physiological turbulence of the body.

The center of the fight/flight response is in the periaqueductal gray (also known as the central gray) which surrounds the cerebral aqueduct of the midbrain (just below the tectum). The central gray is under tonic inhibition from the medial hypothalamus, which receives input from the central nucleus of the amygdala, which receives signals from the orbitofrontal cortex. The central gray activates the autonomic nervous system elevating heart rate, raising blood glucose&adrenalin, etc. Endorphin-containing neurons in the central gray probably play a significant role in pain modulation.

The sympathetic nervous system is dedicated to what might be called emotional responses, whereas the parasympathetic nervous system is more concerned with localized regulation of organ function. Nonetheless, parasympathetic involvement is seen in emotion when, for example, a fearful person involuntarily urinates or defecates. It has not been possible to differentiate the anatomical responses of fear from those of anger at the level of the central gray or below — so it is common to speak of the "fight/flight" response.

Electrical stimulation of the amygdala can produce fear or anger, depending on the spot stimulated. Stimulation of the septum usually results in delight&sexual-arousal. Stimulation of the globus pallidus and the midcenter of the thalamus can produce a feeling of joy.

Fear might be described as a "reflex" of a peculiar sort — a reflex of the autonomic system to an environmental situation which the cerebral cortex regards to be threatening. It is often a conditioned reflex (ie, a learned reflex), but not always — e.g., the "startle reflex" to a sudden loud sound. Although fear may be a deeply conditioned reflex — a phobia of snakes, for example — it can also have highly cognitive associations. A person may be very afraid of pit bull terriers, and yet have much of that fear vanish instantly upon learning that the dog in the old "Little Rascals" film-series was a pit bull terrier. Fear is motivating because it places the organism in a physiological state in which to effectively fight or flee — and in a psychological state to want to relieve the "stress" through fight or flight. Fear and other emotions can also contribute to learning — the close association of the amygdala and the hippocampus is no accident. Emotion means meaningfulness — and we most readily learn & remember those things which are most personally meaningful to us.

Fear is the emotion that has been most studied & thought-about by philosophers, psychologists and physiologists. Attempts to exhaustively and distinctively categorize emotions are a source of dispute among experts. Anger, Love, Enthusiasm, Lust, Sadness, Boredom, Hate, Hope, Jealousy, and many other emotions can be named, but they do not all seem entirely distinct. Jealousy is a kind of anger. Hate seems to be anger in a more hardened form. Anxiety is certainly a kind of fear — and modifiers can further refine the emotion, as in "performance anxiety" or "free-floating anxiety".

Fear seems to be the most widely evident emotion in the animal kingdom, although the emotional repertoire of other species may be as distinct as their physiologies. Dogs seem to show Shame, but it is hard to imagine this emotion in a frog. Shame, Embarrassment, Jealousy and Envy are emotions that are directly connected to human relations. Love and Anger can involve other species. Unlike Anger or Fear, Grief is an emotion that does not appear to motivate. Perhaps, however, it motivates thought, rather than action, thereby leading the subject to re-examine and re-organize his/her life so as to prevent future tragedy. If so, this emotion should be distinctively found in species with a well-developed cerebral cortex — as is the case with the aforementioned "social emotions".

Patients with damage to areas of the right cortex corresponding to the language areas of the left cortex have difficulty conveying emotion in speech and have difficulty understanding the emotional overtones in the language they see and hear. The right temporal lobe is specialized for recognizing the emotional content of facial expression. A patient with damage to the left motor cortex cannot voluntarily smile, but will involuntarily smile in a normal manner in response to positive emotion. A patient with damage to the left anterior cingulate gyrus shows the opposite effect — not smiling involuntarily in response to emotion, but able to mechanically produce an artificial smile under voluntary control. Experiments have demonstrated faster reaction times to warning stimuli sent to the right brain, leading some experimentalists to conclude that the right brain is the source of intention.

An important aspect of personality is the tendency to experience certain emotions. Drugs and surgery have effectively been used against extreme forms of these "personality" manifestations. Lobotomy has been used as a treatment for phobias. Removal of portions of the amygdala has been effective for violent criminals prone to dangerous states of rage. Drugs such as tranquilizers and antidepressants are well-known for their mood-altering abilities.

Physiological correlates have been found that accompany the personality dichotomy "Introvert/Extrovert". Introverts display more cortical blood flow (more arousal) with lower levels of stimulation than Extroverts. A few drops of lemon juice on the tongue of an Extrovert will produce little saliva, but extreme Introverts will salivate profusely. Introverts require a much higher dose of sedative to put them to sleep than Extroverts. Introverts are naturally more aroused than Extroverts (who are driven to seek sensation & stimulation). At the root of these differences are higher levels of norepinephrine (noradrenalin) in the brains of Introverts.

Obsessive-Compulsive Disorder (OCD) is characterized by obsessive thoughts and compulsive behaviors, which can be accompanied by great fear or, at least, anxiety. PET scans show high levels of activity in the orbitofrontal cortex of OCD patients. Atrophy of the head of the caudate nucleus of the basal ganglia (and decreased caudate metabolism) are a frequent finding, although this is less consistent. One of the most effective treatments for OCD is a drug that inhibits serotonin uptake, such as the antidepressant Prozac. Increased serotonin in the orbitofrontal cortex and in the amygdala reduces aggression and favors "social behavior".

Bilateral damage to the orbitofrontal cortex (Brodmann areas 11, 12, 13 and 47) has a notable effect on "moral character". Such patients show a loss of deference for others and a lessened concern for themselves. Their actions show less concern for social responsibility or convention — while at the same time failing to take account of their own best interests. They lose a sense of "right & wrong", behave in a manner that is "crass & vulgar" and may have a difficult time making many kinds of decisions.

The anterior orbitofrontal cortex (areas 11&47) receives inputs from the parvenocellular dorsomedial thalamic nucleus, and it exerts tonic inhibitory control over the amygdala. The posterior orbitofrontal cortex (area 13) receives inputs from the magnocellular dorsomedial thalamic nucleus (which receives inputs from the amygdala and inferior temporal cortex. There are also direct inputs to the orbitofrontal cortex from the temporal lobe, the hypothalamus, the caudate nucleus and the amygdala. (The main cortical inputs to the amygdala, however, are from areas 38&20).

My interpretation of this evidence is that there is an intimate connection between self-awareness and self-image. I believe that much of the basis for deference to others is the protection of self and protection of the image of the self. H.L.Mencken once said, "Conscience is that wee inner voice that says 'somebody might be looking'". Genuine empathy probably involves connections between the orbitofrontal and dorsolateral cortex — the ability to imagine and feel oneself as being inside another person. With such close connections to the hypothalamus and the limbic system, it makes sense that the orbitofrontal cortex would be so implicated in decision-making (linking facts and values).

Although the orbitofrontal cortex may be a center for morality & self-valuation, we must again be careful about over-localization and the homunculus fallacy. The temporal lobe may play a role in "self-recognition" or self-image, and the dorsolateral cortex, while simulating reality & potential reality, must include a model of the self (self-image) — including a model of image of the self held in the minds of others.

There is controversy over whether cutting the corpus callosum produces two distinct "selfs", each with a complete personal identity — one in the left cerebral hemisphere and one in the right. Nobel laureate Roger Sperry has contended that this is true, whereas Nobel laureate Sir John Eccles maintained that the right hemisphere is a mere "automaton".

The left and right hands of a split-brain monkey have been observed to seemingly fight over a peanut. Human patients with a severed corpus callosum demonstrate an awareness with left hand/right cortex which differs from that of the right hand/left cortex. This occasionally even leads to conflicting behavior between the right hand and left hand.

I cannot offer a conclusive interpretation of the split-brain experiment, but I can make a few observations. If the left arm were connected to the thirst center of the hypothalamus and the right arm were connected to the hunger center, I can imagine that the left arm might reach for water and the right arm might reach for food. If there is no homunculus in the brain there may be many different control centers or, at least, control centers may compete for control of action on the basis of competing inputs from different areas of the brain. Using the analogy of the visual cortex V1, V2, V3, etc. areas, control centers C1, C2, C3, etc. could receive inputs from motivation centers M1, M2, M3, etc. and decision inputs from cognitive judgement centers J1, J2, J3, etc. The control center with the strongest inputs may result in action. Severing many of these areas and giving them control of limb L1, L2, L3, etc. could result in actions by the different limbs which are at variance with each other.

Split-brain patients are notable for their loss of creativity. The patients often complain that they no longer dream (or, rather, that is the report from the left hemisphere). Having two hemispheres gives us many of the benefits of double-entry bookkeeping — a certain redundancy allows for the detection and correction of errors. Much of our creativity and decision-making involves resolving conflicting desires and perspectives arising from different brain centers and different cortical hemispheres. Even if cutting the corpus callosum does produce two distinct personal identities, they are both probably impoverished vestiges of the original singular identity. I don't believe that the unity of conscious experienced by a person with an intact corpus callosum is an illusion.