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May 17, 2011
How does our brain, endowed with such powerful but open-ended abilities, acquire complex mental skills through individual experience and culture? What is the brain machinery of the “emergent properties” we have noted, including wisdom, competence, and expertise?We will get to the matters of wisdom, but gradually. In order to navigate an uncharted territory—and the neurobiology of wisdom is such a territory—we must first link it to something better known and better understood: the adventures on memory lane.One of the central points of this narrative is that wisdom is intricately connected with memory—a certain kind of memory, generic memory. Before we can tackle wisdom head on, we need to understand how this particular kind of memory works and how it is different from other kinds of memory. As we will see, a close and direct relationship exists between generic memories and patterns, and between the processes underlying their formation in the brain.All, or at least most, memories are formed and stored in the brain’s youngest and most elaborate part, the neocortex. In addition, certain memories require the support of various subcortical (or to be quite pedantic about it, non-neocortical) structures and other memories do not require such extra support. Those memories that depend on such additional structures are very vulnerable to decay and to the effects of neurological illness. By contrast, those memories that depend on the neocortex alone, and do not depend on the additional structures outside the neocortex, are relatively invulnerable to decay and can withstand the assault of neurological decline, even dementia, for much longer. Most of the memories of this latter kind are generic memories. But what is a generic memory? To understand this, we need to consider some basic facts of remembering and forgetting.What did you have for dinner twenty-three years ago today? Don’t worry. I am just trying to make a point: It is ridiculous to expect that anyone could remember such an inconsequential bit of trivia so many years later. Unless, of course, the dinner was a White House state dinner to which you had been invited. But had I asked you this question one day after the fact, you would have answered it precisely and unhesitatingly, state dinner or not. It was in your memory once, but now it is not; it’s gone, forgotten. Memories for trivial, inconsequential events continue to decay very rapidly every hour following the events, and this decay is characterized by a steep power function. And thank God for that, because had you permanently kept all the memories that had ever, if fleetingly, been formed in your head, your head would be the mental equivalent of a city like Pompeii buried in lava and volcanic ash. Morsels of useful knowledge would be obscured by huge amounts of useless information—informational noise, informational trash.There are some people with the uncanny propensity to remember everything without forgetting anything, although such cases are quite rare. Far from being a gift, this almost without exception proves to be a disabling, paralyzing curse. Aleksandr Luria described a case of a provincial newspaper reporter with the mixed blessing of clinging for the rest of his life to every memory ever formed, no matter how incidental and generally irrelevant. He described the unbearable and self-defeating condition of being constantly overwhelmed by a deluge of overlapping memories and images. Most of us are spared this fate, because what enters our long-term memory store is highly selective and most fleeting memories formed in our heads are not granted this privilege.So forgetting as a normal phenomenon is, on balance, a good thing, as long as it is limited to inconsequential information. But forgetting may become abnormal, caused by various forms of brain damage, and then it is called amnesia. As we will see later, various forms of amnesia exist, as well as various degrees of its severity, ranging from relatively benign “senior moments” to a global catastrophic deficit when the patient loses the ability to remember what happened to him or to her ten minutes ago.Amnesia may be caused by a number of brain diseases. They include traumatic brain injury sustained in car accidents or on the job, interruption of oxygen supply to the brain, viral, bacterial, or parasitic brain infections, diseases of brain vasculature, chronic alcohol abuse coupled with nutritional deficiencies leading to the so-called Korsakoff’s syndrome, or severe seizure disorder, to name a few. These diverse disorders have certain things in common: They are likely to interfere with the brain’s ability to form memories, to store them, and to access them when the need arises. We will revisit amnesia later; but for now let’s focus on the ways normal memories are formed.What do we mean when we say that certain knowledge has become part of the long-term memory store? A new memory begins forming the moment you encounter whatever it is you are learning: a new face, a new fact, or a new sound. The input engages the parts of your brain in charge of the senses, and then some higher-order brain systems in charge of analyzing and processing the new information and relating it to some previously acquired knowledge. This activity changes the very neural machinery engaged in the process, and the resultant change in the neural networks involved in receiving and processing the new information is memory. The process of memory formation has begun. New proteins are being synthesized, new synapses (contacts between nerve cells, neurons) are developing, and other synapses are being strengthened relative to the surrounding synapses. This is the essence of new memory formation.The first lesson to be drawn from this description is that memories are formed in the same brain structures, and involve the same neural networks, that participate in processing the information as it first arrives. In the past, many scientists believed that separate “memory warehouses” existed in the brain, removed from the brain regions originally involved in processing information that was being memorized. Today we know that no such separate “memory warehouses” exist, nor are there any neural “memory trains” shipping information from place A to place B. Instead new memories begin their neural life in the cortex and stay put right there for the duration of their “natural life.”In other words, the perception of a certain thing and the memory of that same thing share the same cortical territory; in fact they share the same neuronal networks. This was demonstrated with great elegance by Stephen Kosslyn. Using a high-tech research tool known as PET (positron-emission tomography), he identified the brain regions involved in mental imagery, the areas of the brain that were lighting up when the subjects were asked to bring before their “mind’s eye” the images of various familiar things. The activated areas turned out to be the same that were activated when the subject would actually see the objects.Likewise, it was fashionable for many years to talk about “short-term memory systems” and “long-term memory systems,” as if they resided in different parts of the brain. This misconception still persists in various professional and lay circles removed from state-of-the-art neuroscience. But in reality these are two stages of the same process involving the same brain structures, rather than two separate processes involving different brain structures.Much in the brain’s blueprint is plain impractical, defying the popular notion that the course of evolution is somehow inexorably and linearly directed toward improvement. For example, our brain stem contains a number of nuclei responsible for the brain’s arousal and activation. They are packed so tightly in a single small area of the brain that damage to this area can in effect wipe out most of these nuclei with a single blow, producing a catastrophic impairment of arousal. This is precisely what happens in coma, which is caused by damage to this strategic area of the brain, the brain stem. A blueprint so devoid of redundancy and backup safety features would have been flunked in any school of engineering or design. A more “sensible” design guided by evolutionary wisdom, had there been such a thing, would have resulted in a much more distributed placement of the critical nuclei responsible for arousal and activation with ample backup and redundancy, so that not all of them end up in one neural “basket.”By contrast, the central feature of our memory machinery, the fact that memories are stored in the same networks that had received the information in the first place, would please any aficionado of design parsimony and economy, and anyone faithfully believing in the “wisdom of nature.” When changes in the network become lasting and robust, the information becomes firmly ensconced in long-term storage. The changes that will have taken place in the network are chemical and structural. Synaptic contacts will have been altered and new receptors formed. The memory thus created will be robust and relatively invulnerable to any assault on the brain, whether it is traumatic brain injury, viral brain infection, or dementia.*22\302\2*
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