The neural basis of memory and learning is the Hebbian junction, the fact that a junction between two neurons, the pre-synaptic and the post-synaptic, can be strengthened (or diminished) when they fire together. This is long-term potentiation, aptly summed up in the dictum “cells that fire together wire together”.

According to an article in “The Scientific American Book on the Brain”, pp. 146-7 (by Eric R. Kandell and Robert D. Hawkins), the molecular basis of this process has been worked out. It depends on a typical cascade process: serotonin released by the pre-synaptic neuron binds to a receptor ca~led NMDA (N-methyl-D-aspartate) on the post-synaptic neuron. The receptor activates an enzyme called adenylyl cyclase, which converts ATP (adenosyl triphosphate, an energy transfer molecule in cell metabolism) to cyclic AMP (which functions as a “second messenger”, serotonin being the first messenger). Cyclic AMP (adenosyl monophosphate) then phosphorylates a protein kinase, which phosphorylates potassium channel proteins, which prolongs the neuron’s action potential and thereby allows calcium channels to be activated for longer periods, permitting more calcium ions to enter the pre-synaptic terminal. This then causes additional serotonin to be sent to the post-synaptic neuron.

According to an article by Joe Z. Tsien “Building a Brainier Mouse” (Scientific American, April 2000, pp. 62-68), the NMDA receptor consists of four protein subunits that form a pore which controls the entry of calcium ions into the neuron. These pores require two signals to open, calcium ions and the neurotransmitter serotonin (o~ in another version glutamate). This forms a “coincidence detector” that associates two brain events.

I am not sure if the two articles describe the same mechanism or two different ones, or if the latter, how they fit together. However, according to Kandel and Hawkins, they describe the molecular mechanism of short-term memory, lasting hours or days. For long-term memory, lasting months or years, the cascade (or a similar one) turns on a gene which produces a calcium-dependent adenylyl cyclase, making the record of the neuronal association more permanent.

Recording memories in the brain is nothing like taping or photographing direct sense-data. The complexity of the mechanisms leaves me gasping, and I may have got it wrong. Our brain knows far more inwardly how to operate than we can fully understand observing it from the outside. The brain is smarter than we are, or at least than I am.

In any case, the basic fact is that neurons that make each other fire form a (semi)-permanent connection, which makes future coincidence in firing more likely. It is like smoothing the path between them, for more efficient passing on of the impulse.

This reminds me of Rupert Sheldrake’s theory of morphological fields (formative causation), the observation that, once a thing has been done, with great difficulty, it is much easier to do it again, even if the second experimenter is far away and knows nothing about the first experimenter’s achievement. (Cf. “entanglement” of two subatomic particles, which change their spins in unison, even if so far removed from each other that they cannot communicate even at the speed of light).This is why the same discovery or invention is so often made almost simultaneously. by two or more people. For example, in chemistry, there are some compounds which are very difficult to crystallize; but once someone has done it, many others can repeat it.

It is somewhat like the story of the “Hundredth Monkey” phenomenon, according to which the habit of monkeys washing their fruit eventually jumped from one island to another, out of sight of the original monkeys, once enough monkeys learned it from each other. It is as if there was a groove in space-time that increasingly facilitated the operation but what could this morphological field possibly consist of?

Could learning of a new process by a bunch of individuals (monkeys or people) or society as a whole be compared to the learning process in an individual’s brain? The mechanism would have to be totally different. But some kind of “wiring together” would have to be involved. For example, can we learn from history, or would we only learn to repeat past mistakes?