beginnings

“Where have I read that at the end, when life, surface upon surface, has become completely encrusted with experience, you know everything, the secret, the power, and the glory, why you were born, why you are dying, and how it all could have been different? You are wise. But the greatest wisdom, at that moment, is knowing your wisdom is too late. You understand everything when there is no longer anything to understand.” ^{^[2]}

-Umberto Eco

Intro:

Memory is simple, deceptively simple. It is like a single beguiling facet of crystal seen in an uncut stone. Should you cut carefully through the rock that hides the crystal, you will marvel at its complexity. So it is with memory. On the surface there is nothing to it. Human memory is easily assessed. Storage in devices from notepads to computer disks, is second nature. But explore memory completely, as an element of cognition, and you will find it to be more complex than is appreciated by the average neuro or computer scientist.

Ask a person to recall three simple objects after a couple of minutes say, "hammer, three and yellow", as doctors do in a mental status exam. People look askance when I ask this type of question. What does it prove? It's an entrée into memory function. Memory is the easiest cognitive function to assess. I used to wonder how memory batteries became part of I.Q. tests. What does a person's memory tell you about their intellect? We all know people who do well in school because they memorize easily and regurgitate verbatim what is taught with little mental processing. People who don't think seem to get the best grades in school.

Nowadays we have less regard for simple memory. Schools claim to teach students how to think, eschewing rote memorization. Students are given open book or take-home tests trying to to de-emphasize memory tasks. Why should a student depend on his memory when we have so many recording devices? Educators tend to lose sight of the fact that creativity is drawn from a storehouse of internal memory, images, words, combinations of words, melodies that are part of us. Creative persons recombine accumulated memory elements in novel ways.

I always admired the way my father recited poetry and literature that he was made to memorize in school. He was educated in the old days and kept these words with him his whole life. It gave him great pleasure every time he recited a relevant piece of verse, something which he loved to do. We don't give our kids that opportunity anymore. They may read a poem, but their teachers reason that this verse will always be available to them, should they ever need it, on some recording device. The teachers may be right about the availability of information, yet they lose sight of the fact that the lines never are revealed to their young minds as well, never mean quite as much, as when they along with nuances and connections become a part of a child's being, repeated and internalized.

Clinically speaking, it is quite easy to tell when someone is having trouble with their memory. They complain of losing objects, forgetting names and appointments more than in the past, going to another room to take something and forgetting what they came for. In more advanced cases they may no longer be able to learn anything new, and forget more well-established things like bridge or chess, or their way home from a close friend or their job. In the worst instances they can't be trusted alone at home for fear they will leave their door unlocked, the oven on, or loose themselves outside. Memory dysfunction is clearly visible to friends and family who notice problems early on well before deficits become obvious in other spheres of cognitive function. It all seems extraordinarily simple. Complexity arises as you consider how memory is woven into a rich fabric of cognitive function. Memory forms the basis of learning and adaptation to one's environment. How does this simplest of mental functions play a role in cognition and the development of the total personality?

Schematically we break memory into three components, immediate recall -- the ability to repeat what has been said, recent memory -- what can be reproduced a few minutes after a stimulus, and remote memory -- recollection of one's distant past. You may be surprised to learn that remote memories are harder to erase than recent memories. Old memories are difficult to conjure up, it is true. They tend to pop up when not interfered with by the laying down of new memory traces (engrams), something familiar to us from conversing with older persons who do not register new memories well. Old memories are stored differently than new ones. Well established engrams arewidely available throughout the brain. Memories that have circuited through the brain often enough become overdetermined, and reside in multiple locations to interact richly with other memories. Few of us will ever forget how to tie a shoelace. On the other hand we have only newly been exposed to recent events which are just now assimilating into memory pathways.

It's still useful to think of new memories as beating a path through a set of neurons and synapses as the process of learning takes place. This is the point of departure of the old theory of Donald Hebb who in 1949 suggested that the physical substrate of memory was a strengthening of connection between neurons, more efficient transmission across the synapse, where nerve cells communicate with each other. The average human brain contains about 100 billion neurons and perhaps one to ten thousand as many connections between neurons, synapses. A memory is laid down when the connectedness between neurons is increased, when a message passes more easily from one neuron to the next across a synapse.

We usually associate the hippocampus in the brain with new memory traces. Hippocampus means "sea horse" since it looks like one under low power of the microscope stuck in the middle part of the temporal lobe. If the hippocampus is removed on both sides or is affected by a disease, a person will no longer be able to learn. New memories cannot be formed. There is some evidence that some simple learning takes place by strengthening connections between hippocampal neurons, that learning can be thought of mechanically as the strengthening of connectedness or facilitation of transmission between nerve cells rather than, or supplemental to, a change within a nerve cell. This involves a pre and post-synaptic neuron. One process that strengthens connectedness between neurons is Long Term Potentiation. This process utilizes excitatory transmitter Glutamate. This creates a situation in the post-synaptic neuron where it can be more easily stimulated by chemical signals coming from the terminals of a neuron synapsing with it. It happens because of the influx of Calcium into the cell. The marine snail Alplysia serves as an experimental model for this process. Calcium affects an intracellular enzyme, Calmodulin. Eric Kandel and colleagues worked extensively with this instructive animal model years ago. There is a complex interaction here in that the post synaptic neuron secretes a chemical messenger that makes the presynaptic neuron more likely to secrete its transmitter. There is some new evidence that what is made by the postsynaptic neuron to affect its partner is the simple molecule nitric oxide (NO). So what is involved is communication that goes in both directions between the pre and postsynaptic neurons, communication that ends up strengthening their interdependence and connectedness. The sum total of increased connectedness between neurons is reflected in a change in the behavior of the animal that is learning. The hippocampus is involved with more advanced and rapid kinds of learning that enters consciousness.

Figure 1: The hippocampus^{^[3]} of the temporal lobe. This seahorse shapedstructure controls the initial stages of memory formation.

Hippocampus

You detect learning takes place by observing a change in behavior. This is true for humans and experimental animals. A snail can learn to withdraw a body part, or a rat can learn a maze after a small number of exposures in order to efficiently find a food reward, probably by the very same subcellular mechanisms as a child learns to spell. His teacher seeks to observe a change in behavior on a spelling or other test. Whereas the child had not been able to spell a word before, she is able to write it perfectly now. She has learned and the test looks at an alteration of behavior.

Scientists have looked at how these learning processes take place within the individual cell on the microscopic level. In order to do this they generalize from a simplest case. After a first exposure, memory needs to consolidate if it is to result in a reasonably permanent effect on the brain. Memory consolidation is expressed in molecular and then in structural alterations in neurons and other brain cells. Recent work has shown unequivocally that protein synthesis is necessary for memory consolidation. Other proteins modulate production form the RNA templates. The chemistry inside the neuron utilizes chemical messengers^{^[4]} , the very same messengers involved in a host of other cellular functions, such as cyclic AMP. Why does the individual cell start to make proteins? The goal is to create new connections between cells, new synapses and parts of synapses, perhaps divided synapses, and the like. Rats learning to navigate mazes require production of specific proteins in the hippocampus. If this process is interfered with, the animals will not be able to navigate the mazes. For the first time we are able to correlate protein production and alteration of the untrastructural microscopic change, with the laying down or recording of memory traces. Once the chemical and structural changes are known this increases the promise of somehow intervening in memory disorders, or even improving capacities of normal. Learning can be made to occur on the microscopic and chemical level^{^[5]}. The new protein production is thus expressed as an untrastructural change observable with an electron microscope. The molecular, chemical and structural changes are then expressed by a final common pathway, behaviorally. The child gets and A on his spelling test.

The laying down of explicit memory is accompanied by ultrastructural changes in the hippocampus and other areas. The brain is not a static structure. It is changing, rebuilding, forming proteins and synapses constantly as it is used. We cannot speak of the brain as having only a static anatomical structure. The anatomy changes as it is used much like a muscle or any other organ of the body. In the brain this change in structure is easiest to see in memory circuits, especially the hippocampus and the mechanism for structural change involves gene products and proteins but is ultimately expressed in formation of synapses or connections between neurons. Disuse and stress may lead to atrophy. Hormones particularly cortisone like hormones and estrogens have been shown to influence this process.

It is easy to see that as soon as we learn which specific molecules aid learning then we may some day be able to influence them. We will know how they are affected by disease, and, even more importantly, we may be able to enhance memory function by altering these molecules.

The memory we think of most of the time, recalling words or methods, is explicit that is, mostly verbal memory. Humans want to be able to recall most of the time in task utilizing their language: names, dates, places, methods of operation and the like. Implicit or non-verbal memory is at least as important as explicit memory however.

Implicit memory is the second type of learning that happens on a nonconscious level. It uses a different mechanism and anatomic substrate. For example you learn motor skills like playing the piano or basketball subliminally and many aspects of this learning which involves practice do not enter consciousness. The anatomical pathways for implicit memory are quite different, especially memory which enhances motor skill. There are a number of different types of implicit memory.

For example, in addition to memory that enhances motor performance at a piano or in athletic competition, there is undoubtedly a similar kind of sensory implicit memory. What allows emotions to surge with recognition, resonate in a fashion, well after a rhythmic figure or theme has been introduced in a symphony, is undoubtedly a subconscious implicit memory mechanism. You hear a brief rhythmic figure in the Berlioz Symphonie Fantastique as he is being led to the scaffold which is "drummed" into the head over and over again. Much later, a similar figure picked up as the Finale closes, has emotion reaching a fever pitch. Most listeners don't even notice it. They just feel the high emotion. Perhaps the composer himself is not aware that he's used this technique because the music being on his mind, he will tend to use the same themes again in any case, much as the writer will, if he doesn't watch out, use the same words or even phrases again in very different contexts. Much of this occurs without a conscious thought, on the part of the composer, or the listener. It happens on a much more primitive level, of course, in popular music, as themes are repeated, often interminably, in a short song that lasts perhaps one or two minutes. What happens a good deal of the time in popular music especially, is that there is such an abundance or repetition, of rhythmic figures, simple melodies instrumentation, harmony etc. as to breed ennui. And thus brings up another type of learning, habituation. A stimulus repeated over and over again, ceases to have much of an effect. After a while your nervous system becomes so used to a familiar stimulus that you barely take notice.

In classical music there is the sonata form, consisting of exposition, development and recapitulation. One or more themes present themselves in the exposition. The development sees new expressive territory being claimed and finally in the recapitulation, the listener is transformed in a certain way, that is, he hears the same or similar themes differently. Jazz pieces use the same basic form, incidentally, with a statement, embellishment ( improvisation) and restatement of a melody. Since this process seems to be so universal, this may hint at somet basic physiological mechanism. We have a mutual maturation process involving composer and listener alike. Otherwise stated, repetition alters the brain's response. Memory has to be there for past to alter the future. The memory could just as well be subconscious, unnoticed, yet it heightens subsequent response.

The hippocampus has vigorous connection to areas responsible for consciousness and emotion^# . Emotion areas of the brain the Papez Circuit, or limbic system, physically connect to memory pathways. James Papez published his observations in 1937 which makes him ancient as far as biomedical literature is concerned. But many of his basic observations are still extremely useful. He noted that the brain could be broken into medial and lateral sections. Medial parts connect most strongly to the hypothalamus which is involved in basic bodily (visceral functions) and is a structure that also helps organize emotion. The lateral parts connect to the dorsal thalamus that is a way station for sensory inputs. The structure of the medial of inner part of the hemispheres is intimately involved with emotion and also memory. Early anatomists connected many of these structures with the sense of smell as this was considered to be one of the most primitive senses in animal evolution (phylogenetics). In particular olfactory (smell) pathways connect very intimately with the hippocampus. Thus memory, olfaction, and emotion are closely allied anatomically. Since many other animals, especially reptiles and mammals, are capable of expressing rage, but only man shows evidence for advanced thought, with these medial brain structures being relatively older in evolution, and with simpler cellular architecture, they are considered to be more primitive, hence emotion is more primitive than cognition or thought. We now have a much better understanding that all of these functions interact, so as to be all part of a larger conscious whole that includes both thought and emotion^{^[6]}. The individual structures and details about their connections may be interesting to some readers but are not at all necessary for purposes of discussion here.

At about the same time, new work was published dealing with another brain structure, the amygdala (for almond, an almond shaped structure in the temporal lobe). Animals that lacked an amygdala were docile, hypersexual, and hypervigilant and restless having a syndrome named for the two scientists who performed this lesion experiment, Kluver and Bucy. This is also a rather ancient concept which has definite clinical correlates in humans. The Amygdala is tied to many of the structures in the limbic system and is undoubtedly involved in emotional expression^{^[7]}. It is not uncommon to see a patient whose personality has been drastically altered due to temporal lobe disease. Often, patients have some or all of the characteristics of the Kluver-Bucy Syndrome and are thus rendered refractory to any kind of medical or psychological intervention.

Figure 2: The Papez circuit. Mamillary body to midbrain (1) and anterio-ventral nucleus of thalamus (mamillothalamic tract) (2), thalamus to cingulate gyrus (3), cingulate to hippocampus (4), hippocampus to mammillary bodies via fornix (5)^{^[8]}.

Papez Circuit (see above)

The connectedness of the memory circuit to the limbic system or emotion centers of the brain is neither coincidental nor insignificant. The post-traumatic stress syndrome links memory to high emotion. Vietnam veterans and accident victims have flashbacks to highly emotional experiences. What is recalled, is the extreme emotion as much as the actual event. Laboratory animals can be conditioned to associate strong emotions such as fear and rage to neutral stimuli such as an animal cage where shock had previously been administered. This kind of association occurs in all of us every day. Conditioning can also be explained on an anatomic basis strengthening transmission between neurons that connect to each other. This is used to explain part or the pathogenesis, the medical cause, of the Post-traumatic stress disorder where sudden intrusions of memories evoke high emotional states.^{^[9]}[1] The emotions associated with certain memories can be used to improve memory function, Memory specialists often use this uncanny ability of the brain, that connects emotions and sensory experiences to increase mnemonic powers.

PET scans show that the amygdala is extremely active in forming memories. One may ask why this is so, since the amygdala is viewed as an emotional center oft the brain. We have seen that it is intimately connected with memory and emotional circuits. Perhaps this is why in sleep when we are working to consolidate memories which closely tied to emotion and emotional expression . Memory and emotion are closely linked.

Emotion that goes along with memory is an integral part of it. I rarely recall dreams but was able to remember and record most of what turned out to be a very complex dream because of a musical theme that seemed to be playing through the dream sequence, much as music plays in a movie. It was a theme played by the high strings and flutes of Prokofiev's Romeo and Juliet that I'd been listening to the day before. The music was supposed to be portentous telling you that something fateful would happen in scenes to follow. In the dream it evoked a totally different emotion, one of ghostlike eerie fear that I hadn't appreciated while listening to the piece. The day after the dream, recalling the music and its attendant emotion, I was able to reconstruct the complex dream surprisingly well, all through the process using the melody and emotion as a sort of mnemonic device. Moreover there since sensory experiences from the day prior are frequently used for dream material it may be that one function of sleep and dreaming is a dry run rehearsal of the previous days events that leads ultimately to the permanent laying down of memory traces. The hunter dreams of catching his prey, re-rehearsing experiences of the day before, reshuffling images, recreating scenes that will enhance his performance the day after. In fitful sleep you rehash yesterday's argument with your boss, etc. Dreams place memories in an emotional context, are intimately tied to the emotional valence of memories. Perhaps this is why the Vietnam veteran typically awakens with his frightening recollection, and why we frequently hear or persons with panic disorder awakening with in panic. It's a lot like "pavor nocturnus", night terrors in small children, who wake up suddenly drenched with the output of their adrenal glands which have been enlisted in support of the nocturnal event, screaming in dread, palms sweaty, heart pounding. Only these little folks awaken without the specific memory of a dream, only the fear and dread that usually comes with a nightmare without the nightmare. Night terrors do not typically occur in REM or dream sleep.

Forgetting is at least as important as remembering. There must be active processes that aid in forgetting, some of which will someday be described on the cellular and biochemical level, just as active memory is described. This would serve obvious housekeeping functions. For one thing you could picture that it would be impossible to function if all of our memories old and new were constantly competing for our limited attention. Imagine if all of your old memory stores kept creeping into consciousness. You wouldn't be able to handle current tasks. You are taking an exam in biology which asks specific questions. Think what would happen if you were unable to keep out of your mind's eye for at least a while what you had learnt in physics the day before. Some other memories, might be more difficult to exclude, from your current attentions, but the point is, some active adaptive process pushes even recent memories out of consciousness, mostly unclutters awareness. Older memories are pushed even further away. Somewhere in our brain (this turns out to be all over our brain and is difficult to localize) is a memory attic which contains relics of our past.

Dynamically trained psychiatrists still talk about repression as a defense mechanism, an active process, pushing old memories out of awareness. This is still a useful concept, but contrary to psychodynamic renderings of the process, it is almost always a healthy, not a pathological process. It is easiest to conceptualize repression as an uncluttering mechanism. As we have seen, dreams from the previous night are actively pushed back into unconsciousness where they belong. For most of us dream content can almost never be retrieved or is brought to the surface only with great difficulty (and very questionable authenticity). This is universal for most healthy functional individuals.

I recall a conversations with a very troubled man in his mid 50's who was plagued with numerous memories of his childhood and unresolved conflicts mostly revolving about his relationship with a now deceased father. Time and again he'd mention to me with great emotion, how his father could never tell him he loved or approved of him, something which obviously hurt him deeply. But it was apparent that he was trapped in a web of old memories. Trapped or fixated in his past, he was incapable of handling the challenges of the present. Some therapists might talk about how important it is to revisit these childhood conflicts with the rational retrospectiscope of a grown adult. The only problem is that in many cases there seems to be a total entrapment or fixation on the thought processes of childhood. Plain repression of these memories would seem to be much more adaptive. Perhaps old painful memories which we push away have subtle and unsubtle effects on our present lives as they influence attitudes and behavior. And so the debate goes on.

Through years of scientific research there have been many theories of how learning takes place. Some of these theories stress what happens inside instead of between cells. They implicate synthesis of chemicals such as nucleotides and proteins. Neurons are analyzed for these chemical constituents after an animal is exposed to certain experiences that change behavior. These older theories are in not incompatible with synaptic theories and there is every reason to suspect that our explanations regarding how memories are formed are very incomplete. Memory function is certainly a composite of many biochemical processes within and between neurons. Even the simplest discussion of memory, the most rudimentary of cognitive functions, reveals that we are trying to deal with many separate processes. We have already mentioned immediate, recent, and remote memory, conscious and subliminal motor memory. The chemical and anatomic substrates for these different processes are not the same. For example, verbal and conscious memory is the type we talk about classically being mediated initially by the hippocampus. For words and symbols that usually require conscious awareness, the hippocampus is the portal of entry into the brain until the memory engram becomes firmly established and destroying the hippocampus will affect short term memory, blocking the initial establishment of a foothold in the brain. But non-verbal performance memory, is mediated by motor systems such as the cerebellum and it is more than likely that performance learning, basketball and piano playing among other things takes place directly within these systems. It is likely that there are other forms of learning as well, but the basic breakdown is into conscious vs unconscious processing.

Figure 3:Types of memory. Retrieval brings memories into awareness. For the most part, emotions, motor and sensory engrams, though not subject to voluntary retrieval, may still affect behavior and performance.

Memory Types (see above)

Clinically a decline in mental function seems manifest first in a loss of ability in recent memory. This corresponds to neuropathological changes that occur first in the hippocampal and parahippocampal areas of the brain, especially in Alzheimer's disease. We all know elderly persons who lose their ability to remember. In some of these persons other spheres of mental effort remain relatively unaffected and they are said to have a benign forgetfulness of aging. In others, loss of recent memory function signals a global decline in cognition termed dementia. This is what happens in Alzheimer disease which is frequently presents with a loss of memory function.

The transmitter Acetylcholine is most closely associated with this disease, and intimately tied with recent memory. A diffusely projecting nucleus in the brain, the nucleus basalis of Meynart shows the most change. The output of this group of neurons is primarily cholinergic and largely to the hippocampus.^{^[10]} A lot of people have tried to help failing memory by increasing this neurotransmitter much as one does in Parkinson's disease with dopamine that is deficient because of loss of Dopamine producing neurons in the brain. All kinds of substances have been used to retard the degradation of Acetylcholine, or to replace this transmitter, some of these dripped directly into the ventricles of the brain to improve memory, all with a very minor effect. The first of these to be FDA approved is called Tacrine or Cognex but it has little lasting benefit and significant toxicity, affecting the liver mostly. The minimal benefit can best be appreciated by sensitive measures such as psychological tests.

It's just because memory is so easy to get at that it seems to have so much philosophical relevance. Computers and libraries have vast stores of information as bundles of bits appropriately labeled, which can be retrieved when asked for. Named bundles of engrams are stored in isolation, retrieved, and operated on in ways defined by a user. It is reasonable to ask whether the brain functions as a repository of information in the same way as a computer or library. Surprisingly, The answer is that it does not.

For humans the laying down of memories is equivalent to maintaining the continuum of consciousness. Time is continuous and we reckon and follow it on the basis of stored past and newer experiences. Our past serves as a basis for comparison but it also colors perception and action. This is what we mean when we talk about learning or memory. We expect the laying down of a memory engram will make some enduring change in thought, emotion or behavior that we will be able to measure. If there is no way to determine that a difference has somehow been wrought, then the effect of memory is imperceptible. On the basis of what has been laid down before we are made to see things in different ways. Each old memory trace may be more or less critical. For example, a traumatic childhood sexual experience not only changes adult sexual encounters but colors all subsequent experience. Much of the work of classical psychotherapy is breaking a traumatic or maladaptive link between emotions and current events, and re-establishing connections with previous repressed memories. What is truly fascinating is that this seems to occur whether or not specific memories can be specifically retrieved^f . This continuity of experience is perhaps the most important determinant of personality structure. A human life is a chain of experiences encoded in memory that is a continuous flux of maintained consciousness.

It is undoubtedly true that experience alters our personality, our response to environment, even though the precise memory of that experience may not be specifically retrieved. Whether or not you can recall an event, it alters your subsequent person, it changes you. This implies that an experience may will alter the information content of your brain, but that specific alteration cannot always be tested for. Perhaps this is analogous to explicit or verbal memory versus implicit memory. Philosophically it is apparent that every experience alters us. A sinner who truly repents and changes his ways, is somehow better than a pure person who has never made a mistake; a person who has tested his mettle through suffering and has later been redeemed, is far better for this experience than the person who has gone through life without any struggle at all. Redemption alters us in subtle and not so subtle ways which may not be so easy to document on tests of explicit memory. Undoubtedly such experience changes us in profound ways. Thus it seems that sin and suffering serve a specific purpose, which is a galvanizing of the personality. This would be a classical explanation for the biblical concept of redemption. But is the ability to retrieve specific memories important or not? A tough question.

This has implications concerning the meaning of life and death. Consider the possibility that a soul or personality is reincarnated after death, not just discarded by posterity, but simply transmigrates into a different vessel, a different body. Typically persons who believe in such a doctrine reason that we are not aware of this because memories of our past lives are inaccessible. At first blush this seems to be an absurd notion. After all, a soul with no access to its past is a new creation. But the past may not be entirely cut off from the present. It may be difficult to get at, especially for those of us unskilled at the proper technique. More importantly, it may come out in subtle ways and may still color present experience in much the same way that our own living memory does. Even so reincarnation of the soul is hard to swallow at least for Westerners because memory is for us the contiguity of existence. When continuous formation of memory traces stops a new line of experience, in essence, a new being, emerges. In one sense, life and death, creation and destruction may be defined this way, a break in sequential memory. But here lies an even more critical point. There is more to human memory than simple retrieval of information bits in storage. Memories, meaning our past, even if not specifically retrieved, change present and future experience. Memory, arguably the simplest of all cognitive functions, may take on an almost mystical significance. Some persons claim that they can bring back memories of a previous life through extreme hypnotic regression, that memories inaccessible to our waking existence can be brought back via hypnosis. There is as yet no scientific evidence that hypnosis improves retrieval under any circumstances and none to support the notion that hypnosis causes the true elicitation of childhood and other forgotten memories. Observing hypnotic sessions, one comes away with the impression that the hypnotized subject is manipulating the therapist but under the best of circumstances no one has ever proved the veracity of a hypnotic regression into childhood or into past life.

False Memory

Most supposed hypnotic recollections are really works of the imagination. This is especially apparent to scientifically-minded folks who look with a jaundiced eye at recollections of infancy and past lives. Where does memory end and imagination begin? This is a most difficult question to answer for the subjects of hypnosis, assuming that they are not out-and -out malingerers or fakes.

False memories have been subject of a lot of attention in recent years. There are celebrated cases of child abuse and sexual misconduct such as one involving the Catholic Archbishop of Chicago and The McMartin preschool case in California that saw the conviction of six preschool teachers, ruining their lives, on the basis of recovered memories induced by "therapists". The question has been how much if any of the data provided by these small and highly suggestible children were true memories and how much was fabrication. Recent work with PET functional brain imagery of Daniel Schacter and Larry R. Squires^{^[11]} attempts to differentiate true from suggested memories on the basis of the PET image. The memory of an actual memory of a word read to and heard by the subject would be retrieved utilizing the auditory portion of the brain, an actual word seen would be retrieved using the visual area, etc. indicating that memories partly reside in the sensory cortical areas involved when they are laid down and later need to be retrieved using these same areas. Numerous psychological studies have shown how easy it is to create memories, especially in suggestible children and certain adults.

Memory and imagination^{^[12]} are both abstract non-material entities comprised of pure thought. Some of this manipulation of ideas may be non-verbal and subconscious. How do we know, when we are creating something, that we're not simply reaching down into our memory stores and placing ideas in a new juxtaposition? A good deal of creativity and synthesis involves bringing up memories in a new light. An inspiration, or solution to a difficult question hits us when we least expect it, most often when we are not even working on a problem that is consuming our attention at the time, but more often during random activity. This sudden inspiration, has been noted by a number of creative persons. For example in the words of mathematician Henri Poincare^{^[13]}:

"Most striking at first is this appearance of sudden illumination, a manifest sign of long, unconscious prior work. The role of this unconscious work in mathematical invention appears to me incontestable, and traces of it would be found in other cases where it is less evident. Often when one works hard at a hard question nothing good is accomplished at the first attack. Then one takes a rest, longer or shorter, and sits down anew to the work. During the first half-hour, as before, nothing is found, and then all of a sudden the decisive idea presents itself to the mind. It might be said that the conscious work is more fruitful because it has been interrupted and the rest has given back to the mind its force and freshness. But it is more probable that this rest has been filled out with unconscious work and that the result of this work has afterward revealed itself to the geometer just as in the cases I have cited; only the revelation, instead of coming during a walk or a journey, has happened during a period of conscious work, but independently of this work which plays at most a role of excitant, as if it were the goad stimulating the results already reached during rest, but remaining unconscious, to assume the conscious form."

All of us have experienced the same process so well described above. It happens when we lose something and suddenly, never when we are looking for it, remember where it was. This recollection comes to us in a flash. And we just know that what we have recollected is accurate. Isn't it exactly the same when we have been working on some puzzle or problem, that we experience a sudden flash and the solution is ours. These points are so inspiring because in an instant we just know we have come upon the right solution; all of it just works out so perfectly we almost need no verification. You can observe this for yourself in hearing people solve puzzles on TV or radio. Many of them make the same observation. But the more interesting question is whether any of this is pure memory or imagination, or even if there is a difference in these two aspects of pure thought.

Some people lose the ability temporarily to store new memories. A condition known as Transient Global Amnesia, is most probably caused by blocking the blood supply to specific regions of brain. We know that if only one side of the brain is affected memory registration will not be affected. The problem has to affect both sides of the brain at once. The subject with TGA loses the ability to form memories for a few hours. During that time, he is exceedingly uncomfortable and feels disoriented as if in a cloud, asking questions pertaining to time and place time and again, forgetting answers given almost immediately and is concerned about this. After the episode there is no recollection at all for the period of time for which memory was affected. Sometimes this seems to occur after some kind of exertion or trauma just as if a blow or concussion has occurred. In one case TGA was occurred repeatedly in relation to sexual intercourse^{^[14]}.

Another condition that breaks the stream of awareness of life is syncope, or simple faint. Of course any epileptic seizure that disturbs consciousness will do the same thing. But syncope is interesting for one reason. Interrupt the blood supply to the brain and a faint occurs. It happens with a drop of blood pressure. If the heart, for any reason stops pumping blood to the brain efficiently, you will faint. How long does it take to lose consciousness once brain stops getting blood? Almost immediately!! This is quite remarkable and one wonders why this is so.

The brain metabolizes glucose and needs oxygen continuously in order to make energy. It is one of the most voracious consumers of energy in the body. Other tissues can switch into alternative energy sources when necessary. When you exercise for a while muscle, sensing a diminishing supply of energy, with the liver overwhelmed in its ability to supply constant amounts of glucose, switches to the consumption of fats and can also depend (briefly) on anaerobic glycolysis so that energy can be utilized without a constant high concentration of oxygen. Not so the brain.

The brain requires a constant blood supply. Otherwise it will stop functioning right away and a person will faint. If left for just a few more minutes there will be irreparable damage or even brain death. This underlines a certain fact about the brain. It is an information storage and manipulation device needing to be constantly connected to its power source. The brain resembles a computer that is on and storing and manipulating data. Cut power for even an instant and the thing shuts down. Whatever program you were working on is lost. One wonders why the brain couldn’t have been designed in a different way, perhaps with the ability to switch immediately to its own “battery” or energy supply for just a few moments when necessary. It seems when awake, the organ is revved up and utilizing to the hilt immediate sources of energy, glucose and oxygen. After one or two minutes or so without any blood, the old informational content can still be gotten back. When consciousness returns after this short length of time, you are still the same person.

Also in the brain, as everyone knows, neurons are, as a general rule not replaceable. This is in contradistinction with other organ systems, the liver, the gut, skin, blood and so forth where cells are replenished constantly and rapidly. Injure the intestine, kill cells by the millions and they will grow back very fast. Why not in the brain? Of course that is because every brain carries information built into its anatomy and transmitter and electrical patterns. Nerve cells are not replaceable because new nerve cells will not have the same informational content. Information and experience, life in other words has a certain immediacy. The same holds for instruments which store changes in time or even keep time. A constant source of energy is required. That is the reason for that little battery in your clock radio why everything is lost when your computer’s power supply gets interrupted.

The chain of recollections that defines continuity of consciousness is broken, but the situation is still different from that of reincarnation in that it is still possible to reach back and recall experiences of the just slightly more remote past and also to continue to record future experiences in a stream of mental awareness. Even so, the person with TGA is very troubled by the void in memory long after this temporary process is over. This is so even when as usually happens, family and friends inform him of events relating to the specific time frame that these events occurred. Other's recollections of events in one's own life aren't satisfactory. A vacuum or discontinuity, however short, must be filled.

Diversion: why time travel is not possible:

Memory determines a stream of awareness. Breaking this stream of awareness is very uncomfortable. An hiatus is difficult to deal with. It is only memory that changes us as we journey through our lives from our past into our future. History gets recorded in our mind. I think that's why it's so difficult to fathom, why for nuclear physics, time can stretch and contract and just as easily flow backward as forwards in some instances. The best example is the Feynman diagram in which nuclear particles collide and create other nuclear particles, for example a neutron will split into a proton and electron liberating some energy. This process can just as easily flow backward as forward as long as conservation laws are respected. This is intuitively impossible for us in our real macroworld. According to physicists the main reason time does not flow backward is the tendency of a system to increase disorder or entropy, the second law of thermodynamics in other words. Drop a porcelain cup on the kitchen floor and try as you may, you'll never be able to put the thing back together exactly like It was; things tend toward disorder, and you can't correct your mistake, turn back the flow of time. This is the humpty dumpty effect, "All the king's horses, all the king's men.." can't make things as they were. But this is only part of the reason why time flows only forward for us. The major reason is memory and the workings of consciousness and the brain, our own peculiar physiology, in other words, not physics.

Figure 4:Typical Feynman diagram^{^[15]} in which two pion particles are formed from the collision of proton and antiproton particles. This could just as well go the opposite direction in time with the pions forming the proton and antiproton.

For humans there is an immense difference between the past and the future. In the past something occurred, it alone and of itself. But the future is unknown and filled with alternative possibilities, only one of which will actually happen. This is particularly true if we introduce free will into the equation. The past and future are asymmetric and not interchangeable, for the past is one hundred percent determined but the future is at best probabilistic often chaotic. As the future is subjected to time's arrow and becomes part of the past, it is recorded in conscious and unconscious memory (it becomes history) and the uncertain turns into certainty. The flow of time is thus asymmetric, and the past is recorded in our mind, altering forever future experience. The Second Law of thermodynamics seems so theoretical and flimsy, not good enough an explanation for what we all know to be true for all of us. Time travels in one direction, forward. The most important explanation, has to do with how our mind's work, consciousness and human intuition about time's irreversibility. Even if the backward flow, the undoing and redoing of events is theoretically possible, it is not possible as a mental event, not unless we can fundamentally alter mental processing, which some day we may be able to do. Time travel may thus depend as much on changing mental processes as it does in manipulating physical laws.

Figure 5: Time's arrow. As the past blends with the future in our present, one becomes many possibilities, so that one can't turn back. Free will, exacerbates this process, expanding alternatives unpredictably.

Figure 6: History diagram. At each branch point only one of a number of possibilities actually occurs.

Let us suppose for a moment that one could go back in time. One of the major problems that a lot of people pick up on is that the act of going back and reporting on the past has to alter the future. The reporter who does go back then returns to the future is sure to alter the course of events. This is so even if he is a fly on the wall, invisible to those experiencing their present. When the time traveler returns to his world in the future, his present, his knowledge of the past is sure to alter his subsequent behavior as well. And the time traveler is even more apt to make changes if he is able to travel into his own future. He is sure to wish to change the course of events by his foreknowledge of what is to come. This problem can be obviated simply by destroying the time traveler's memory of what he has experienced in his travels but then things be just as if he hadn't made the journey through time at all!

But that is not the biggest worry with time travel. Every moment in time, as the figures show, is a branch point of alternative possibilities. Only one of these possibilities actually occurs. Then events continue until almost immediately another branch point with alternatives again occurs. At any point it is just about as likely that things could have turned out a different way.

Biologists have noted that life on earth as we know it is due to specific developments as branch points. Scientists have to admit that even on the earth, life and sapient life probably would never have existed but for a very improbable chain of events. Preplanetary gases had to have coalesced into what we know as the earth just the right distance from the sun making our planet like Goldilocks' porridge, neither too hot nor too cold. Floes of molten rock inside the earth had to have created a magnetic field which blocked the lethal effects of radiation to make life possible. Specific conditions perhaps heat and lightening had to have existed to juxtapose and give sufficient energy to simple organic compounds in order to make life which at any event had to eventually become self-replicating. The cell had to have evolved the way we find it today, with the aid of prokaryotic parasitic invaders which carried with them mitochondria and chloroplasts, remnants of simpler forms that make the cell and cellular energy handling possible. Photosynthesis had to have served as a chemical process that freed oxygen to make an atmosphere for aerobic life to survive. Cells had to have gotten together and specialized to make more advanced complex animals and plants come into being. Explosions and extinctions of groups of organisms had to have taken place in highly specific ways. Dinosaurs and not mammals could well have ruled the earth but for the accident of an enormous meteorite impact upon the planet etc etc. In other words, biologists sensing that life as we know it on earth is the result of highly improbable alternatives are less sanguine than physicists and astronomers about life as we know it especially sapient life, existing on other worlds. Even if you look upon life as some kind of self-organizing complexity, still one has admit that life as we know it on the earth, is the resultant of a specific chain of happenstances. Things might well have ended up a whole lot different even on our beloved earth, in other words, without us!!

We begin to appreciate an indeterminacy. If you can look back and you see that things could just as well have turned out different or you begin to see the future in the same way, all of a sudden you realize why time travel is impossible. You will not be able to travel along the precise path of possibilities you were on; you will be sure to lose your way among different alternatives. You may get stuck on a different time line or, put differently, alternate universes. Maybe you will end up in a different world that only has prokaryotes or lacks a magnetic field and has no life at all. If you ever travel in time you can be virtually certain, you cannot go home again.

This implies that the inability to travel in time is tied to the uncertainty, the indeterminacy of the universe. For time travel to be possible the universe must be deterministic, alternatives at branch points need to be fixed, established. Our lack of conception of time travel is thus as strong an argument as there could be, against determinism.

Dream memories are stored, affect us subliminally, but are difficult to bring to any form of surface awareness. Most of us can't recall them in any detail and we are hard-pressed to attach any specific meaning or context to them. Even so, they affect at the very least, the feeling tone of subsequent experiences and color perceptions. I've often had the experience of acting and feeling as if a dream event were true while in reality, it was a mental fabrication. Only after noticing that what I'd assumed couldn't possibly be true did I realize that I must have in fact dreamt it. Certainly thought involves a kind of simultaneous layering. A lot of times we find ourselves trying to manage even juggle feelings. Feelings come to us from contradicting forces-- present reality, manifest thought content, and dreams that lurk in the background of thought. We are handling simultaneous realities, our present conscious stream of reality and a subliminal illogical dream-driven thought stream. The incompleteness of recollection of active thought processes of sleep shroud them in mystery. Ancient dream interpreters were accorded supernatural powers and even in modern society are held in high esteem from Joseph to Daniel and Freud to Jung. Still, there is every reason to believe that at least two continuous streams of consciousness interact and operate upon each other even though the memories are not made manifest. We know that details of immediate past experience form the previous day, often apparently inconsequential details, are incorporated into the content of dreams. Conversely, dreams imperfectly remembered while awake influence mood and beliefs. Your wife or your child having appeared in a dream experience at night may color your interaction with your family the next morning. Mental engrams may be operated upon and may interact without even being specifically recalled.

Memories of events from actual experience are difficult to reach. Details inscribed in certain portions of our brain may still be inaccessible. Perhaps you've experienced this while at a gathering introducing a person whom you know and anxiety momentarily blocks a recollection. Tests in school engender the same kind of anxiety that blocks recall. The answer may enter your mind only after you've left the room. Details of earlier life become inaccessible merely because events are too distant to be pertinent to our current situation. This is a service that are brain provides for us, the sorting or packing away of memories, an uncluttering of immediate experience. Old useless memories are almost irretrievable.

The difference between people with super memories as opposed to the rest of us seems to be a matter of memory retrieval, not storage. To utilize a memory you have to have done two things: It has to have been written down somewhere which in the brain means there has to have been some structural alteration in the brain that results in the memory's having been stored. Next you have to use some mechanism to retrieve the stored memory. The reason why you can't recall something is frequently a matter of getting at, retrieving, the stored memory trace. Storage involves lower brain structures such as the hippocampus and some other areas adjacent areas too, the thalamus, entorhinal area that lie beneath the highest levels of the brain, the cerebral cortex. But retrieval, recruits cortex especially. Consequently it is retrieval that is most vulnerable to changes in level of consciousness.

Thus we have an anatomic model for a memory engram or any thought or sensation reaching consciousness. In order for us to be aware of anything, a memory, a sensation, pleasure or pain, it has to stimulate the highest areas of the brain, the cerebral cortex, responsible for consciousness. The stimulus has to have caught our attention, that is aroused the gray colored cell bodies at the surface of the brain. Example: an unconscious person is unconscious because the lower brainstem levels have failed to arouse the cerebral cortex which is not awake or aroused. You squeeze a finger on the hand of the subject. He withdraws the hands and winces in discomfort. But he is not awake and aware. Does he "feel" the pain? The answer is that he does not feel it. In order to experience or feel, one must be conscious to the stimulus, awake and aroused. If the stimulus does not reach consciousness and despite intact automatic behavioral responses, withdrawal and wincing, there is no pain^Y . The anatomical substrate of conscious awareness is the cerebral cortex. In order for us to be aware of something, it must take hold of cortical neurons, something needs to direct our attention to that particular thing. This is what we mean by retrieval. Here widespread cortical excitation, attention, is directed to a specific memory engram dredged up from the past. It is taken out of storage, comes to our attention and is thus retrieved.

It's been demonstrated time and again that memories are very well recorded. They can be elicited with certain techniques such as hypnosis, the use of certain inhibitory drugs such as short acting barbiturates and by electrical stimulation. Some of these methods relax a person, help him get past any anxiety or distraction impairing retrieval^# How are our memories ordinarily retrieved? One model assigns to each memory a specific anatomical location. Your recollection of your third birthday party may be stored somewhere in the temporal lobe perhaps adjacent to your memory of your second birthday. In thinking about your second birthday or birthdays in general you might elicit memories of your third birthday party. This has some relationship with experience certainly. Electrical stimulation of the brain would seem to support this anatomical model. Memories are retrieved by somehow specifying anatomical coordinates in a three dimensional brain, much as a song is found on a record as the needle alights on a certain track.

Another far more useful model for memory retrieval is described by the grea