11.2 Biological Basis Of Memory
I tell you something today and you repeat it back to me tomorrow. In the interval, it must have been retained somewhere somehow in your nervous system. Karl Lashley devoted a lifetime to find where and how this "engram" was stored [LASHLEY]. He finally concluded that he could not find it anywhere because it was everywhere. Memory is stored in every cell of your body. Karl Pribram, one of the three brilliant young men who developed the TOTE unit, later reached the same conclusion when he argued that the nervous system contains holograms rather than photographs. Every element in a hologram contains the whole image.
James V. McConnell suggested that it may be stored in ribonucleic acid (RNA), a biological cousin of deoxyribonucleic acid (DNA). He was the leader of a group of psychologists who studied learning in worms [MCCONNELL]. A worm was taught to turn right in a T-maze by arranging that there was some nice mud on the right and a shock on the left. They minced up the worms and fed them to other worms, and found that those cannibal worms took significantly less time to learn to go right than worms which had fed on untrained worms. Since all that survives being minced and eaten is chemistry, this information must have been transmitted chemically. Subsequent research pointed to RNA as the relevant chemical. This research was not refuted in the usual way by replicating the experiments and getting different results. It was simply ignored [INGRAM, Pages 77-86]. It did not fit within the paradigm current at the time.
This conclusion, which seemed preposterous at the time, is now if not obvious at least less preposterous. With the breaking of the genetic code, we now know that the "memory" our species has acquired over hundreds of thousands of years of evolution is stored in DNA in every cell of our body, we may be more open to the argument that the ontogenetic memory each of us adds to this phylogenetic memory during our few decades on the planet may be stored in RNA in every cell in our nervous system.
However, even if we concede that this is how memory is stored, we need also explain how it is acquired and retrieved. Even the simple-minded metaphor of memory as a data bank requires a distinction between the processes of deposit and withdrawal and the process of storage. When you withdraw a hundred dollars from your bank, you do not expect to get the same 5 20-dollar bills you deposited the week before. You know that that money has been assimilated into the abstract whole of the bank's assets.2 The most popular thesis is that learning (deposit) is the creation of a neural circuit by breaking down the gaps between cells and remembering (withdrawal) is the reactivation of this circuit. Donald O. Hebb hypothesized that such circuits, which he called cell assemblies, are created in the cerebral cortex [HEBB]. Subsequent research reveals that the lower brain plays a role in the creation of such circuits.
As you are adding up a column of figures, you keep in mind the subtotals after each figure. It would serve little purpose to retain all this information since you need it only for a short time. Nature has ingeniously designed a dual memory system consisting of short-term memory for such functions and long-term memory for storing information which may be retrieved later. In the former case, the impulse does not cross the synapse (the gap between the cells) often enough to create a cell assembly. The hippocampus, a structure in the lower brain, plays a role in the transformation of short-term into long-term memory.3 It replays each cell assembly - consciously when you recall it and unconsciously when you sleep - to stamp it in during the early stage when it is vulnerable to extinction. Such a dual system removes the clutter of the sub-steps in a process, unlike our clumsy computers which retain every keystroke.
Further dichotomies show that memory is more complex than we may at first assume. During a personal energy crisis, I bought a bicycle. Though I hadn't ridden a bicycle for 40 years, I hopped right on and rode it right away. Two weeks later, I couldn't ride my bicycle. I had forgotten the code for the bicycle lock. Surely the memory of how to ride a bicycle, which had survived for 40 years, is qualitatively different from the memory of the code, which did not survive for a few days. Memory experts indeed do make a distinction between procedural memory (riding the bicycle) and semantic memory (remembering the code). Such procedural memory is a function of the putamen, a structure in the lower brain. Nature thus contracts out memory for action to a system which reliably retains this information.
Wilder Penfield found evidence that memory is localized in a particular place within the cerebral cortex [PENFIELD & ROBERTS]. He was operating on patients suffering from epilepsy by removing the area of the brain which triggered the epileptic seizure. He dropped an electrode into the brain of the patient to make sure that the affected area is not part of the speech centre. If it was, the cure would be worse than the disease. When he dropped the electrode into the temporal lobes of patients, they reported experiencing events in their pasts. (Such an operation can be conducted while the patient is fully conscious, since there are no pain receptors in the brain.) It was a rerun of a past event with all the accompanying sights, sounds, smells, tastes, and touches. When Penfield lifted the electrode and dropped it again into the same place, the relived experience continued where it had left off. It was as if the patients had a complete videotape of their pasts which could be played by triggering it with an electrode.
He had located a site of episodic memory, where the content is in the context of one's life. It is of course a heavily-edited version containing only the sliver of whatever was available in your environment. The sliver is chosen by your amygdala, another structure in the lower brain, which controls your attention. Semantic memory becomes abstracted from episodic memory when it is removed from the concrete context in which it was learned. Subsequent research reveals that the amygdala consolidates the sights, sounds, tastes, smells, and touches, from the various reception areas for those senses in the cortex into a single "episode". The elements of the episode remain in their respective reception areas. Thus, triggering any one of those elements (as Penfield did) resurrects the whole episode. Once again, nature ingeniously designs a system which provides many "handles" to retrieve our past experiences.
Every type of memory thus involves a structure in the lower brain - the hippocampus, the putamen, and the amygdala are involved respectively in long-term, procedural, and episodic memory (see Figure 11-1). This lower brain is a primitive layer of our brain which we share with all mammals. Thus memory has been a function of our species for a very long time. There is much talk about the evolutionary function of speech, as the essential difference between us and the other animals. However, it would be of little value if not combined with memory, which we share with other animals. Memory enables us to benefit from our own experience, whereas memory-and-speech enables us to benefit from the experience of others. We differ from the other animals not so much because of learning but because of teaching. However, we are not separated from our animal past. Our old brain still plays a role. Indeed there is much more traffic from the old brain to the new brain than from the new brain to the old brain. We remain wired for emotion rather than for reason.
Helen Keller reported in her autobiography that, when her teacher Ann Sullivan poured water into one of the hands and wrote "water" on the other hand, she suddenly realized that the word "water" represented water [KELLER]. That is, that something can be a symbol for something else. She rushed around demanding the symbols for familiar objects. This eureka moment was the beginning of a process which transformed a blind and deaf child into a competent and scholarly woman. There was a similar moment in the development of our species, when symbolization linked memory to speech. Perhaps the Big Bang of the Brain had more to do with the merging of memory and speech than with the acquisition of speech itself.
Traditional evolutionary theory describes the process as gradual. However, some evolutionary theorists suggest that it may sometimes be sudden, and cite the Big Bang of the Brain as a prime example [GOULD]. This debate, whimsically described as evolution by creeps versus evolution by jerks, could be resolved by the argument that the formation of modules is gradual but the linking of modules could be sudden. It's very unlikely that a module for speech or a module for memory could suddenly appear but it is possible that the merging of those modules could be sudden.
Memory (however nature designs it) is the foundation of all media (however we design them). This primacy of memory is recognized from ancient mythology to modern medicine. In Greek mythology, Mnemosyne (memory) was the mother of the nine muses: Klio (history), Melpomene (tragedy), Thalia (comedy), Kalliope (heroic poems), Urania (astronomy), Euterpe (music), Polyhymnia (song and oratory), Erato (love and marriage), and Terpsichore (dance). Those muses were the "media" of that time. However, Mnemosyne is still the mother (or grandmother?) of Teevee, Telephono, Multimedia, Internete (or whatever we decide to call our modern muses). Modern medicine recognizes Alzheimer's disease as a disorder of memory which destroys the very identity of the patient. Relatives of Alzheimer patients are horrified as they watch the person they have known and loved gradually disappear even though their bodies are still here.
No matter how sophisticated our media becomes, it is important to remember that it all rests on the foundation of Memory and Speech. It is merely an extension of the communication system created by nature. With the fourth generation of Multimedia and Internet, we have finally created a system in which the storage and the transmission of information is integrated within a single system. However, we are simply plagiarizing nature, which integrated the storage of information (Memory) with the transmission of information (Speech). The fact that Penfield found a memory centre near the speech centre suggests that Mother Nature has devised some ingenious integrated memory-and-speech system to provide us with our first generation of media to store and transmit information. We don't yet know how she does it. The search continues.
2 Changes in bank architecture suggest that bankers and their clients are aware of this. Banks built like fortresses of stone and steel to protect the money have been replaced by banks with open offices showing clients the activity that generates interest on this money.
3 The hippocampus is also involved in spatial navigation. London cabbies are required to acquire "the knowledge", involving 37,000 roads and 320 routes between important points within a 10-kilometer radius of Charing Cross, to qualify for their licenses. Scans of the hippocampus revealed that their hippocampuses were significantly larger than average and grew with the job.