VI

WHO ARE WE, THEN ? − Memory

Memory can be defined in various ways, or better many kinds of memory can be defined. It can be decomposed into many simple or complex functions, some of them already present in worms, others only in man, and each of them can be considered as one aspect of memory.

The response to a stimulus that is applied repetitively decreases: if you wish, this already is some kind of memory, isn’t it? But the response can be restored by associating other stimuli; this happens even in very dull marine mollusks, which this way appear to “remember” what has happened. And who is unaware of Pavlov’s experiments, who made his dog’s mouth water by ringing a bell? Riding a bike (a bear can do it) or playing the saxophone (a brighter subject appears to be needed here) also require that memories (motor schemes) be “fixed” somewhere in the brain and that it be possible to recall them. And one could go on with much more complex examples...

Usually we think of memory as a more specific function: the capacity of fixing memory traces that persist for a long time, rather than their momentary registration. Our interest therefore focuses on the process of memory consolidation: a term that suggests that the question is, after having carved a trace in the clay, to let it dry and cook it so that it does not get spoiled. This is precisely the way one generally thinks about memory traces: sensations, sounds, images, captured and etched in some hidden spot in the brain − in some protein? in DNA? − and preserved for the moment one will want to fetch them back. Computer culture reinforces this vision of memory as an “archive”. But memory − as it takes place in our brain − is instead an active process that does not approach at all the ideal of accurate and reliable preservation of documents: it rather is a mutable game of notes and drafts and sketches, that tells a lot about the owner, and maybe even more on him than on the matter that has been archived there.

If you freely follow this line of thought, you may wind up supposing that the owner, in the end, is precisely what is archived there... Memory as personality and identity, my story as I have lived it. An this is not so extravagant, because each activity of the nervous system leaves a mark, be it labile or permanent, that is not only a trace of what has happened: in the meanwhile, it constitutes a modification, slight and imperceptible as it may be, of the way the system will react to other signals in the future.

Memory is not a repository, no.

Memory is you.

Memory is not even what you are made of, that is not enough, it is you.

Memory grows and changes, memories are not closed boxes, they change with you. Reality, sensation, emotions create reticules of activity and relationships among the hundreds of billions of neurons you are made of. Yes, you are made of neurons, of neurons your mind is made. Sure, you are not your neurons. But each unimaginably complex reticule of activities and relationships, each moment of the activity of your brain, that changes at every moment, is an instant of your life, of you: and this is you. It is more or less like music: it is not the piano, it is not the cords that vibrate, but strictly speaking it is a vibration of air. It talks to us, it moves us, it appears as an energy and an incorporeal magic, but its essence is nothing but air and its capacity to vibrate.

But what do we remember?

Memory. It does not tell our past, but the signs it has left in our soul...

“In any case, when we recount our past each of our breaths is a lie”.

Why? what emotional, metaphysical or supernatural force pushes us to do that?

Actually, not necessarily we “do it”. A car that appears to proceed in a strange way not necessarily does it because the driver is drunk; sometimes it is the car itself − sometimes a fault or a defect − sometimes it is precisely built to work like this.

Many people, in talking about memory and reminiscences, are surprised of imprecision and re-elaboration, as if they mourned the precision of a computer in recording data.

Actually, there are regions, in the brain, dedicated to fixing information, in an associative way: an object as an association of sensory features, names for objects, people and relationships, a word as a sequence of characters, a limerick as a sequence of words, or even better as a sequence of movements implied in repeating it. They are specific regions in the brain and cerebellum. And they do work well.

But a great part of memory has nothing to do with this secretarial work, a job for meticulous archivists. It is something much more complex, evanescent under many respects, and under many respects greatly more fascinating. And precisely those who complain about malfunctioning, imperfections in memory working − as if they envied the inflexible and inarguable precision of electronic memories − seem not to realize that they would deny the slightest possibility of a hint of soul to the computer; and not so much because the Council of Trento only conceded it to the women, but simply because the computer cannot invent its own reality, live it: it just records it.

What makes the difference is the path the memory follows, between him who records it and him who reads it.

We do not recall with our eyes, our hands, our heart.

Before anything arrives where something can be recorded, in the brain, there is a long way, elaboration, interpretation.

We remember interpretations, and we reinterpret them in recalling them.

Is this a defect? In my opinion no, it is there that soul is born.

The sensory datum (a sound, an image, a perfume...) reaches the cerebral cortex, and it is re-elaborated at every passage, dematerializing into a collection of relationships and schemes. The raw data are digested and decomposed in a thousand different ways by many different cerebral structures (no more images but lines, colors, masses, volumes, contrasts of lights and tones, geometrical shapes and faces, unknown or well known...), and what is recorded is many activity schemes of specific groups of neurons. Each activity scheme represents a trait, a characteristic, a way of looking at the sensory datum.

Each coherent activity pattern of neuronal cells tends to be fixed if it repeats (or if it occurs in a moment of intense attention or emotion): if a network of neurons is activated in a synchronous way several times, the connections among these neurons are strengthened.

The pattern of neuronal activity that corresponds to a datum of experience becomes fixed and our experience is thus recorded within us. Actually, more than within. It becomes part of ourselves. In the end, this is what we (our identities) are made of. This is the way we grow, the way we change...

And we easily go back to these moments of our past: the brain “recalls to memory”...

The networks of neuronal activity evoked by reality, by sensations, by emotions, that are fixed when there is emotion or repetition, tend to come back and reactivate when the involved network of neurons is activated, even only in part; this occurs whenever we live a sensory, cognitive or emotional experience that is at least partially coincident. Thus, the brain easily recognizes the features that correspond to schemes that have been already acquired, and the construction of a new memory can employ such schemes, that are already present, and in turns it completes and enriches them.

In the last thirty years we have made great progress in understanding memory processes; but if one does not look at it the right way it is easy to overlook the relevance of what we have understood. We now know cellular mechanisms by which the efficiency of a synapse (the site of contact and communication between two neurons) changes as a function of previous activity: the synapse is strengthened or weakened, and the effect persists for many minutes, or hours, days; it may even trigger permanent modifications of the neuronal “network”.

A change in synapse efficacy may not seem a great thing: memories, language, thought are something real different! But these processes of synaptic plasticity are progressive and associative: synapses that are activated together are stabilized and strengthened more and more (or in some cases are progressively weakened). This way schemes of coordinated activity of neurons, even very complex ones, can be consolidated, thereby “fixing” sensations, mental states, memories.

This is what continually happens in “working” or “parking” memory regions, where modifications only persist for a short time: this way we can repeat a telephone number or recall a name for a few minutes. This is a limited room, that must be continually reused: if a trace is not refreshed it fades and gets lost. But if a scheme is repeated again and again it will be reproduced and “fixed” in less dynamic cerebral regions, where plastic alterations are more persistent, and will constitute a permanent memory item. As any student well knows, if we reread tomorrow what we have studied today, and we re-examine it again in a few days or weeks, we shall not forget it (it has gone to the cortex!), whereas in a month we shall not be able to recall anything of what we study in a hurry just before the exam.

The schemes of coherent activity by neuronal cells tend to be fixed when they are repeated. If a reticule of neurons is activated synchronously several times, the connections among these neurons are strengthened, and the activity scheme tends to reappear every time the reticule of neurons involved is at least partly activated, when the brain lives a similar activation state, i.e. when we live a sensory, cognitive or emotional experience that is at least partly coincident.

Thus, what reappears, or persists, or comes back in your sensations, in your thoughts, in your emotions, is fixed and consolidated. It will be recalled every time a new experience activates in part the same neuronal scheme, i.e. when “something reminds you” of it. And you will recognize it as part of a personal patrimony, as yourself; and when you meet it again you will recognize both the experience and your own reaction as parts of yourself.

However, also what is not recognized, what is new, is fixed. Provided you are attentive. And it is integrated with what you are, it becomes yourself, the you that changes.

It is sufficient to observe postures and expressions: each expression and posture we assume, each gesture we perform, reproduces a scheme of activity of neurons from various parts of the brain, that predispose and perform movements. There are few things that you feel more as yours own than your expressions, your typical gestures; you continually reproduce them. But if you reproduce several times new ones, in order to study them, or by unconscious imitation − this happens a lot to children, but also to us, with the persons we love − then these become yours as well...

What is new gets fixed if you are attentive, and you are so if you are alert, tense. Even more it gets fixed if you are upset or troubled by emotion. We shall discuss this somewhere else, but emotion, and particularly fear, arises from the unconscious recognition of situations of great relevance for the survival or the well-being of the organism: some deep regions of the nervous system are activated an they not only alert the whole brain, but also fix all present perceptions, recording them as possible indirect signals of an emotionally relevant situation, as important details that might in the future warn in time about a danger, or a possible emotional gratification.

What is new gets fixed. Better, the schemes that represent new experiences get fixed. Because each scheme that is generated, that gets fixed, is indeed a response to reality, but is not the reality in itself: it is your way of receiving it, your response, a complex framework, rich of cognitive aspects, but also emotional, and affective, esthetic, volitional, visceral ones. And they are yours.

It is your response, it is you in front of reality.

It is you, but in the meanwhile you change. You change because now that instant of your life also has become part of you. From now on, the coordinated neuronal activity scheme that represent it will tend to turn up every time you activate a part of it, and will recall this same instant; and the more intensely you have lived it, the more inexorably the neuronal scheme will reappear.

Each similar experience will propose you that moment again. If you pay attention, you will realize that you are not living it again identical, you will notice the differences. This is important, it may be crucial to react properly. But noticing a difference in the scheme makes you fix a new scheme, similar to the old one, that will confound the memory, enriching it with new shades that were not there before. If you do not pay attention, you will simply feel as if you simply lived again something you already know, as if you simply WERE something you had already been before. But in the meantime, the subtle game of neurons − strengthening interactions with whomever is in tune − can gradually erode the etching of your memory trace, and make it more and more similar to what you are living now, to how you are living it now.

Each new frame of activity that is generated in the brain is a way of assimilating the world and the experience (making it as similar as possible to what we already possess, and to what we already are). But as we assimilate we also change. And the more we care, we are affected, hit, troubled, upset, emotional and passionate, the more we change.

You may say the most original and sharp and extravagant thing that one can think of, there will always be somebody who honestly and sincerely reacts as if you told him something he already knew, he already saw, he already thought of. Sure, already seen everything: it is sufficient not to pay attention, not to care, not to detect the differences, what is new, not to get involved... Still, etchings get eroded (less so, perhaps, if you stick to the idea that you have nothing to learn, and you can see only what you already know). And everybody changes, at least a little: in every moment you are no more the same, and even those who already saw, those who knew everything, even they are no more the same. You are no more the same, materially: those who love themselves a lot, exactly as they are, may not like it at all, but new connections are established and strengthened or weakened among your innumerable neurons, and you will no more be able even to reproduce (recall) how you used to be, precisely. Thus, at every moment you try and assimilate but in the meantime you do change − another metaphor of the general rule of life, changing in trying to persist − you change because in every instant each reticule, each scheme of activity that you would recognize as yours, as yourself who already lived it, has actually become richer, and different.

New and different as is a word, used many times, that one day you find in a poem, charged with a color, an emotion, an atmosphere that it had never possessed before. That word will never be the same in your vocabulary, and all your language will not be the same, because now it has a new instrument, renewed and re-adjusted, capable of rendering novel shades and perspectives.

Yes, just like this, our memory − and each of us, after all − is like a language, like the language of a child, who may possibly become a poet.

Each word that the language acquires enters it with a meaning, a semantic value, an esthetic value, an emotional value, an affective value, and a color and a rhythm. Each time its sound will occur, its sequence of written letters, the concepts and emotions linked to it will appear. But each time they may reappear associated to objects, concepts, emotions, colors, tones, rhythms that are different, possibly unexpected, often surprising. So the word itself changes, gets enriched, its light and color change, its tonality, its agreeability, its evocative power, its music, its commitment.

The language changes, and the child does become a poet, or maybe a lawyer. Or an engineer, or a stylist...

But language, considered this way, is personal. individual. To each of us each word has a different sound, emotion and color. Is it then something strange, if we often do not understand each other?

Sometimes it is easier to remember stupid things, the text of baby songs, the names of the characters of t-v serials, or even the absurd ones of videogames, and people may experience great difficulty to learn by heart things they consider important while unwanted, irrelevant rigmaroles keep rolling in their mind. Maybe this is also a way of setting back, under the pressure of changes and novelty, to familiar sounds and words, unimportant, perhaps, but reassuring.

Because memory is also this, feeling home with what one is acquainted with. As it is true for life in general, memory is driven by the eternal conflict between affirming and recognizing oneself − to protect from novelty and change − and curiosity, the need to interact to change and be changed, to live.

The brain preserves a multifaceted representation of each of our experiences, based on numerous schemes of coordinated activity of nervous cells. For each new sensory datum it will easily detect the features that correspond to already acquired schemes. The construction of the new memory trace can thus make use of the schemes already present, and in turn it completes and enriches them. Memory is not a photographic film, that is exposed and thus captures the image; it is an active process of assimilation of incoming data with the ensemble of information previously acquired: thus, what drives it is not the faithful reproduction of reality, but subjective perception, mostly determined by previously recorded information. In these terms − a dynamic process in building as well as in saving, updating and recalling remembrances − memory is not at all reminiscent of a dusty archive, but rather reminds language, language that evolves and grows: a set of objects-words that live in the relationships that reciprocally link them, and in generating and sketching new objects and relationships, in attaining new meanings and richness.

The same way as words sometimes seem to detach from the objects they represent, and assume new meanings and colors, as if they were animated and alive, thus our memories, conceived and kept alive, grow and transform with us, like words employed each time in a different context; when we recall an old memory we rebuild the scheme of neuronal activity that corresponded to it at that time, but we do that in a brain that meanwhile has changed, in which new meanings may have been associated to the activity of each group of neurons. And the memory turns up different, it is an experience that the momentary ego rebuilds, not the experience that was “fixed” long time ago. Though some aspects of the memory, and specially emotional ones, may be perceived as, and may actually be, genuinely identical.

Memory is then an imprecise recording device, flawed by prejudice and remodeled. An imperfect machine? Well, it may be so, if you wish to say so; but were not it so, how could it enable us to give a “meaning” to an image, to a sound, to life itself? It is an instrument that interprets while it records. Imprecise, distorted? So, what? This is only a further reason to exchange impressions and opinions with other similarly imprecise observers of reality !

As one learns to speak, the same way one learns to remember.

For one who possesses few words it is a hard work to acquire a new word, to perceive its richness and complexity, to learn to use it in all of its expressive power. It is not strange that for the young child, though he has great potentiality of synaptic plasticity, few fixed memories and “lots of room” to accumulate new ones, it is less easy to fix new memories, or rather that his memories may be even more intense but are less precise, detailed, rich: that is because there are not myriads of other memory traces with which to build a new one in all its facets and relationships, in all its complexity.

The poet, who deeply knows the word and its origin, who can eviscerate its semantic implications and metric, musical, evocative properties, who knows many ways to tell the same thought, will not be put to silence by simply stealing some words from his vocabulary. Similarly, an active memory, oriented to capturing relations in reality rather that fixing static images, based on a continuous re-elaboration of one’s own knowledge, by putting it in relation with ever new data and information, will display a much greater resistance to deterioration by time and age: notions are forgotten and lost, but the mesh of conceptual references that entraps them − culture − remains.

We have learnt to take care of our body: hygiene, attention to what and how much we eat. The same or an even greater attention should be dedicated to our mind. The emigrant, who comes back after many years during which he has not been speaking his mother tongue, looks as if he had not only forgot many words, but also lost his proficiency in using his original language to correctly express himself... The same way as language is enriched by speaking and parches in not using it, so memory as well, the crucial instrument for any higher cerebral function, rusts with age if the stimuli to keep it exercised are lacking: the deterioration of mental abilities in many elderly people is caused not only by diseases, but also by dereliction, social neglect, loss of affective relations, lack of physical and specially mental exercise.

The concept of memory that emerges from this varied picture is multifaceted and under certain respects contradictory and elusive: one thing and a thousand different other things in the meantime. The vision of memory as a process of fixation and reproduction of schemes of neuronal activity, in fact, leads us to extend the concept of memory and perceive its multiplicity. Neuronal plasticity is present and active in most structures of the nervous system, specially in cortical areas, although it is more or less marked in various areas. And each region, characterized by its own way of elaborating and “interpreting” specific information, will exhibit its own form of memory. Actually, in the field of cognitive sciences the term “memory” is almost never used alone, but as a vague category of cognitive activity. Today the study of memory is based on precise classifications. Memory is classified as declarative, explicit, communicable in words and conscious, on the one hand, and non-declarative, implicit, non verbal, automatic, unconscious, on the other hand: procedural memory (skillfulness, ability, habits, motor schemes), priming and basic associative learning (conditioning). Memory subsystems are considered and described: episodic memory (remember that), semantic memory (know that) and procedural memory (know how).

THE PROCESSES INVOLVED IN VARIOUS ASPECTS OF MEMORY:

Priming

Areas of sensory elaboration are mostly able to fix schemes that correspond to sensory experiences, ready to be activated to recognize aspects of experience already encountered previously. Is it memory if we recognize something seen before? This is exactly the technical meaning of priming, as opposed to naiveté, something in between preparation, predisposition and loss of virginity. This is not a clear or uncertain and elusive (but anyway conscious) sensation of familiarity, the so-called déjà-vu of an old aroma, no, it is something much more elementary, an acceleration of the reaction capacity to a stimulus that has been presented before with respect to another one never previously seen, a rearrangement of neuronal circuitry, to which a more or less clear perception may follow that something has been recognized, but such perception will be elaborated by other areas of the brain, areas that are in charge of meta-analysis and semantic evaluation, interpretation, awakening and pointing of attention... Here are the cellular bases of something we already discussed: in experience, the response of the brain is different to what is known and what is new. Priming is a fundamental process in memory, and relevant at least as much as surprise: both call for attention, one because it suggests familiarity, responses already tested and customary, support and safety; the other because it demands hesitation, doubts and change, and the slight vertigo of curiosity and discovery. But these latter aspects do not concern memory, this is reading and meta-reading of what happens in regions of sensory elaboration, following changes that are linked to memory, by systems of “higher” elaboration and interpretation.

If this process of recognition is strictly related to sensory activities, a very similar process also occurs in areas of complex elaboration and correlation among sensory modalities: in those areas, schemes of agreement among various sensory modalities are fixed that enable to recognize objects, relationships, features, and to learn conceptual readings and interpretations. There is no reason to think that priming phenomena be absent from cortical areas and circuits involved in even more complex elaborations, that will enable detecting and fixing logical aspects more and more abstract, up to the coalescence of symbolical systems, with the consequent impressive evolution of the possibilities of learning and rational elaboration.

Aversive and operating conditioning

Many sub cortical circuits operate to produce adequate reactions to dangerous situations; many signals (odors, images, events) that are indifferent to an animal species are danger indicators for another, and can determine instinctive reaction of “fight or flight”.

But in addition to instinctive reactions, it is necessary for animals as it is for us to learn to recognize and fear what constitutes a danger, even where instinct does not help us. This is a rather important aspect of memory; it may not be as exciting as other aspects, under the philosophical point of view, but certainly it is not less relevant for survival. The learning capacity of the amygdale (a deep nucleus in the temporal region) sustains these processes: simple associative mechanisms account for how the amygdale can fix relationships between elements − simple or complex − of experience and danger situations, thereby learning to generate alarm, avoidance and defense reactions when an irrelevant stimulus is associated several times to an unpleasant, dangerous or painful signal or stimulus (this is called aversive conditioning). The circuits that undergo plastic changes to sustain this learning presumably involve structures external to the amygdale, such as the cerebellum.

Similar neuronal mechanisms may underlie other analogous forms of learning, such as operating conditioning: the repeated association between a behavior (e.g. pressing a knob) and a prize (e.g. receiving food) can guide the acquisition of a new behavior.

Also in this case the changes in the responses are aspects of learning in a strict sense, but they underscore the presence and activity of other processes of great relevance: the simple detection of alarm signals (whether instinctual or learned) or the association between a gesture and a prize do not justify, per se, modifications in behavior. It is necessary that there be structures and circuits, in the nervous system, capable of both learning and intervening as motivational forces (drives), thereby modifying instinctual responses or generating autonomous behaviors, even with no awareness.

Classical conditioning

The place in the central nervous system where associative mechanisms dominate is the cerebellum, a structure that contains more than a half of the total number of neurons in human brain. It coordinates entire groups of muscles and activities in various regions of the encephalon; at any instant, it compares the motor orders output by the brain and brainstem with their results, and it intervenes to correct and modulate when needed: an extremely powerful and rapid servo-control, that permits attaining maximal accuracy of motor and behavioral responses and their rapid and dynamic tuning. Lesions to the cerebellum impair rapidity, calibration, accuracy, fluidity and automatism of movements: if the cerebellum is injured, an aimed movement (for example bringing a finger to the nose, with one’s eyes shut) becomes uncertain and oscillating, when it departs from the optimal pathway it is overcorrected, goes beyond the target and must regress.

The cerebellum is an enormously powerful system, organized in a repetitive, modular and systematic way. It receives a “copy” of all sensory information − from specific senses, vestibule, muscles and joints − and, through a separate pathway, a “copy” of all output and input signals to and from muscles and visceral organs. On one of these two pathways the cerebellum possesses billions of synapses in excess, which may combine to modulate, activate or inhibit complex responses of the nervous system; many of these synapses are continuously inhibited, and switched off in the long term, if the other pathway happens to be also active on the same neurons. Thus, the circuitry in the cerebellum keeps changing, as a function of the relationship between sensory information and motor orders.

If a particular stimulus or situation comes about in the moment in which a response is being performed by the organism, the cerebellum learns to generate this same response each time that same stimulus or that particular situation occur again. This is the basic circuitry that permits classical conditioning to occur: a slight blow on the eyes each time a ring bells, and I shall blink every time it rings in the future.

The aspect that one may overlook, but is very important to understand the relevance of a learning system of this kind, is that a lot of information reaches the brain, concerning the position and the movement of muscles and joints. Thus, performing a specific movement constitutes a sensory picture, a “situation”, and if this movement is accompanied or directly followed by another movement, twice, three, one hundred times, the sequence will become automatic. Then, it will be finely and rapidly controlled by the cerebellum, with no need for attention and consciousness, and will be performed more rapidly and precisely, automatically, indeed. And after a sequence of three keys pressed on the piano the fourth will come by itself, better not to think about that if you do not want to make mistakes, or anyhow interfere with the fluidity of the sequence of movements.

Yes, it comes by itself, like “Klaus” after “Santa”. This servo-control circuitry for reproducing sequences is too useful and efficient, as concerns any automatic aspect of elaboration, for it not to be used by cognitive elaboration areas as well: if it is not necessary to compute how much is three times four, this is because the cerebellum suggests the automatic answer “twelve” much more rapidly than you can compute it. And it repeats poetries and prayers learnt by heart without interfering with our thinking of something else (who has not tried this? it even appears there are at least three levels: automatic repetition in the background, a me who thinks of something else, and another me who clearly realizes − observes from above, satisfied − those other two thinking machines in my own head); and it incessantly controls endings and grammatical and syntactical concordances, consecutio temporum and order of the words in the sentence, leaving the brain at our disposal for thinking of WHAT we want to say and HOW we want to say it.

Pretty useful, this little machine that works there behind, in the back of our head, to simplify our lives. At least in those situations where it is good to simplify, in the name of efficiency, as in t-v quizzes, where you must have the answer, possibly the right one, but above all rapid, because stopping to think about it is like getting it wrong...

Implicit and explicit memory

The most thoroughly studied structure in the nervous system, from the viewpoint of learning and memory, is the hippocampus. It is an important structure buried deep in the temporal lobe, with some regions of the temporal cortex specifically associated to it. In lower animals, actually, it constitutes a major fraction of the whole brain.

Many circuits in the brain are extremely plastic during development, and this accounts both for the maturation of sensory and cognitive capacities in the embryo and in the infantile age, and for the impressive learning capacity of the child. Once adulthood has been reached, plasticity phenomena become more limited in many area, but they remain very active in the hippocampus and some other specific structures (such as amygdale, cerebellum and many cortical regions).

The role of hippocampus is precisely in this extraordinary plasticity: connections and circuits get remodeled at all times, so to fix the occurrence of associations, coincidences and sequences, and to fix them more deeply and for a longer time, the more frequently these relations re-appear. Hippocampal plasticity is typically associative: inputs that reach the same neuron together, or arrive on it in rapid and reproducible sequence, are reinforced, for minutes, hors, days, and thereby consolidate the writing, into the circuitry of the hippocampus, of networks of relations that can assemble a context for any sensory or cognitive information. Hippocampus operates contextualization of the incoming information: in lower animals it sustains spatial memory (learning the way out of mazes); in man it sustains the task of inserting new pieces of information in the extremely complex network of experimental and symbolic relations that constitutes our knowledge. The memory trace is complex, in the hippocampus, intricate and rich of relationships, it is an “explicit” description of experience, easily mapped on a symbolic and linguistic system: it can be verbalized, at least in the brain of an animal such as man, precisely capable of symbolic elaboration and language. This is opposed to the other associative memory aspects discussed hereto, that were mostly aimed at creating connections between stimuli and responses, or within logical or behavioral sequences, that are fixed and operate with no need - often with no possibility - of explicit reading and verbalization.

THE MODALITIES AND THE SYSTEMS OF MEMORY

As above mentioned, several subsystem can be recognized: episodic memory (remember that), semantic memory (know that) and procedural memory (know how).

Episodic memory is declarative and refers to subjective experiences. Recalling the memory trace does not reproduce the episode, but reconstructs it based on how the subject has lived it, and the remembrance is manipulated with time, as the reference context of the subject evolves. This is an important aspect in attributing truth value to a remembrance: it has been clearly demonstrated that the subjective remembrance of an episode one has assisted to can be substantially modified by simply talking about it repetitively and “convincing” the subject that the episode was different from what he recalled. A suggestion for Italian speaking readers is to look at the book “Testimone inconsapevole” (Unaware witness) by Gianrico Carofiglio.

One portion of the temporal lobe is particularly involved in this kind of memory: actually, electrical stimulation in that region induces the sensation of déjà-vu, that elusive but strong impression of having already seen and lived this moment, so exactly and precisely...

Semantic memory also is declarative and refers to meaning; it is intrinsically linked to aspects of association and generalization, to language, in general to “interpretation” of experience. It is a complex function that involves several distinct areas of the brain: structures in the prefrontal cortex (those regions that we shall see as implied in focusing attention) while one is searching for a remembrance; hippocampus in phase of memorization, and especially in contextualization; and large areas of the cortex for memory consolidation, depending on the kind of knowledge involved: spatial relationships, hierarchies, order, mathematical relations, principally in the parietal lobe; classification of objects, instruments, faces and names, principally in the temporal lobe; strategies, propositions and projects, principally in the frontal lobe.

Procedural memory, finally, is for a large part implicit, mostly depending on basal nuclei and cerebellum, but it also involves the frontal lobe, and pre-motor areas in particular, for its explicit and “verbalizable” aspects.

Two further systems implied in memory and learning have been clearly described.

The first one is a perceptual representation system, semi-automatic, principally linked to recognition, mainly comprised of

• a visual subsystem for word/form recognition (visual cortex): this system recognizes with a great efficiency, for example, the word, and extracts it from the written context, rapidly proposing plossibe redanigs, bsaed on the egeds, and mtosly on the frsit and lsat ltteer, mcuh bferoe an atnettive and dtaelied eaxm is prefrmoed. Or not?

• an auditory subsystem for word/form recognition (auditory cortex), which continuously proposes, while you hear, hypotheses of subdivision of the flux of sounds into phonemes and words, and makes it possible to choose the most meaningful sequence to rebuild a sentence even from interrupted fragments; this way sometimes it happens you hear wha... smb ..els h’nt sed, but you really do hear it, to the point that you may end up discussing even heartedly, “you said that!”, “no, maybe you interpreted that”, “no, I heard perfectly well that you did say that”...

• a structural subsystem for pre-semantic recognition of the structure of words, objects or anything else that can be characterized by a structure (here the temporal-occipital junction is important); this subsystem obviously has a central role in both recognition processes cited above.

The second important system is “working memory”, that is a series of cerebral structures that are in charge of retaining for a few seconds sensory and cognitive information to make their cognitive elaboration possible. This is an executive central “working space” with two servo-systems: a phonological loop for testing and recycling small amounts of verbal information, that is not involved in long term memorization (it makes it possible to retain the phonemes recognized in the speech heard up to now, until the interpretation of the word or sentence is completed, to rehearse it and to repeat meaningless sequences − such as a telephone number − without remembering them after a few seconds); and a visual-spatial notebook for the short term retention of visual and spatial information, which involves several cortical areas and helps detecting and analyzing changes, movements, evolutions and processes, by means of continuous comparison of current and recent past information.

In summary, memory with all its sophisticated complexity turns out to be a set of refined functions, partly connected, partly independent and partly subordinate to other neuronal systems of elaboration. A set of functions that − one by one − admit a single, precise neuronal base and display operative modalities that can be studied in detail with experimental approaches, and that are today reasonably clear in their fundamental characteristics. However, those who begin to be bored now are right. Up to here we have discussed mechanisms of information and procedure fixation, learning mechanisms, that cannot be said not to be related to memory; but memory, what we normally mean by memory, the thing that captivates us and we recognize as a part of us, as ourselves, is something else.

Correct, indeed. It is also true that all processes seen up to here operate, some of them identical, some others less sophisticated, in animals as well. On the other hand we have mostly discussed about sub-cortical structures − amygdale, hippocampus, cerebellum − or about sensory areas of the cortex. But if in man it is the rest of the cortex that makes the difference, the associative multimodal areas that read, compare, combine and interpret the information that each brain system elaborates, if the rest of the cortex is what sustains abstraction and symbolic elaboration processes, then it is obvious that in man there exists another kind, another level, another mode of memory: the possibility of fixing, learning and remembering representations, analyses and interpretations, descriptions and intuitions, and of re-reading them as a complex and live matter, of writing an explicit and conscious story of reality and life, one’s own history.

Here, we find ourselves once more trespassing limits, we again encounter the meta, a different dimension that poses new questions, asks for new eyes, and brings us elsewhere. Once again we face the elusive dimension of awareness and consciousness, a trait that occupies a good deal of the soul: its neural base flees, it bounces us once more to metaphysics, myths, spirituality and faiths.

One cannot stop here without dedicating some attention to this dimension of memory, memory as history, our own history. An entire world, rich of fascination and mystery.

Taken together, al these functions make it possible to “write” in the brain (in the connections among nerve cells) events, data and circumstances, information and knowledge, that constitute our history. A history that is not told from the beginning to the end, but rather intermingled as a big box of old photos, knocked over and put together again by a curious child: you will find, close to one another, old photographs that are somewhat alike or have similar colors or shapes, or share a detail, and may possibly come from points incredibly distant in time and in space. Indeed, this is the way our history is written, closing a page every night, day after day, but continuously going back to old notes to add and delete, redraw, collect on one day memos that were written at the seaside and on another day the letters to mum, or the tickets of the library. What a history is that! if something is missing, something that should instead be the axis of history, that something is time...

No time. Sure, regions that analyze temporal sequences may be able to order schemes of experiences, to remember and recall events and actions, seen or performed. Areas and systems involved in controlling motor procedures may offer their contribution to such restorations. But indeed, each remembrance is a picture of neuronal activity recalled and proposed again in the brain, abstracted and isolated from time: memory, as a capacity of recalling past sensory experiences, is fragmented and without time. A memory trace can refer to a sequence, a process, a succession of gestures and words, but as a whole, as a single compound entity, with no temporal continuity with other traces. It suffices to think of how difficult it is to recall whether something in our life has happened before or after something else: sure, we can associate a date, an employment, a social or familiar condition, that lets us easily spot the period, possibly the exact date, but certainly in our memory that event is not close or connected to the events of the preceding day, there is no rewind or fast-forward button, there is no ordered succession, there is no scanning. Rather, there is a sketch of places, people, events, emotions, ideas and projects that draws the background of an epoch of our life and permits us to locate in a relative and absolute time each of our remembrances.

There are times − those of each experience, gesture, action, event and sequence that we have fixed in our memory - but time is not there.

Because of this, what most fully and precisely resembles us − as we precisely are now − is indeed our memory: not what we have been, but what remains in us, of what we have been. And everything here, now, not in a line that wanes away; everything here, more ore less deep and more or less hidden, concealed or well highlighted, all present in guiding our thoughts, our choices, our fantasies and desires and dreams. Each of our thoughts is affected by what has passed through our body, our mind, our soul, in every moment of our life. It reflects our history but does not tell it, time is not there. The same way as culture is not what we know, but the sign that has been left in our soul by what we have learned, so we are our memory. We are not our history, but the way we have lived it and we see it today. What our history has written in our soul.

"Tame me," said the fox...
"What does that mean — 'tame'?"
"It is an act too often neglected," said the fox. "It means to establish ties."
"'To establish ties'?"

"Just that" said the fox. “...if you tame me, it will be as if the sun came to shine on my life. I shall know the sound of a step that will be different from all the others... And then look: you see the grain-fields down yonder? I do not eat bread. Wheat is of no use to me. The wheat fields have nothing to say to me. And that is sad. But you have hair that is the color of gold. Think how wonderful that will be when you have tamed me! The grain, which is also golden, will bring me back the thought of you... Please — tame me!" he said.

... So the little prince tamed the fox. And when the hour of his departure drew near

"Ah," said the fox, "I shall cry."
"It is your own fault," said the little prince. "I never wished you any sort of harm; but you wanted me to tame you..."

"Yes, that is so," said the fox.

"But now you are going to cry!" said the little prince.

"Yes, that is so," said the fox.

"Then it has done you no good at all!"

"It has done me good," said the fox, "because of the color of the wheat fields."

[THE LITTLE PRINCE − Antoine de Saint Exupery]

Links. Connections. This is memory

It is not the elements that make the space; it is the relationships. And emotional relationships − and memory − keep you in the space of your history. Imagine traveling in an unknown territory, fog, possibly, no indications, no building, trees, rocks, cars that might remind you of somewhere else... The main sensation would be vacuum, unreality. Precisely because of the lack of connections and links with the reality around. The experience would reproduce under some respects the essence and angst of schizophrenia, the severe form of psychosis characterized by a fracture between the emotional and cognitive spheres: the impairment in establishing appropriate connections with the surrounding reality leaves the patient disoriented in space and time and heavily impairs its capability of producing a coherent thought, and reasoning in a way appropriate to the situation.

Even more dreadful is the thought of being deprived of our memory... That would isolate us from reality, and even more from OUR reality, from all that we love, from people we care, from all that has been and is important in our life.

Because our history is our memory. Of all the life we live, not WHAT happens to us, but HOW we live it remains in us. And it constitutes perhaps the crucial aspect of our identity, the way out from the dilemma “am I simply what is written in my DNA” or “am I simply the sum of what has happened to me”: I am the sum of HOW I HAVE LIVED what has happened to me, and how I lived it was written in what I already was. This is my history...

At any time, we are writing the memory of our future. We do that as individuals, we do that as a society. But each one does it his own way. Each one lives reality his way, giving attention to this or the other aspect, detail or emotion, link, memory or fantasy. And what we live remains written there, in our memory: it is not an encyclopedia, or a telephone directory, it is a tale, to be read and reread playing with time and space, along unpredictable paths.

Memory as a tale. A tale which does not follow a single thread, but can be told starting from any point and jumping here and there, following rational, emotional, musical, evocative links. And each of us as a language, a personal color, sound, emotion linked to each word. Remembrances like words, memory like a language. But a live language, rich of complex and mutable relationships, of unexpected colors and ways of escape.

It is not the language of the encyclopaedia, no. It is the language of poetry, rather.

A language made of meanings, but also of images, emotions, evocations, capable of rhythm, music, emotion. And a memory that is easily carried away, like ourselves, by images and emotions, and runs away and comes back, or gets lost in evermore faraway and unpredictable evocations.

Thought itself, on the other hand, looks like a tale. A poetical tale, that follows a thread, but at all times can evoke images and other paths in which to get lost.

APRIL is the cruellest month, breeding
Lilacs out of the dead land, mixing
Memory and desire, stirring
Dull roots with spring rain.

[Thomas Stearns Eliot]

Mixing, confounding memory and desire...

Indeed, what is real difficult is to keep them apart. Is there a signal − which one? − that distinguishes in our brain a representation that is a memory from another one that we would like it were a memory? If there is one, it is an uncertain and labile signal, as suggested by the facility with which our memories evolve, are deformed and deceive us. Maybe it is only a qualification that is associated to them, perhaps the linkage with the word “true”, or “real”. Maybe because of this man has always be looking for a god, a principle, a harmony that taught him what is true and real. Maybe the whole history of philosophy is nothing but a search for criteria not to confound fantasy and reality, not to mix memory and desire.