“In Search of Memory”

In Search of Memory, by Eric R. KandelI’ve been reading In Search of Memory: the Emergence of a New Science of Mind, by Eric R. Kandel. Kandel won the Nobel prize in physiology or medicine (funny how the “physiology” part gets left off so often) for his work on the physiological basis for memory. In other words, he was studying how memories get stored in the brain.

I don’t recall how this got onto my list, let alone into my mailbox, but I’m glad it did. The book combines autobiography with a great deal of readable science.

One dimension that appeals to me is the insight into specific steps on the path to understanding the brain (as much as we understand it). I’m no scientist, but I enjoy seeing how things operate behind the scenes, and Kandel shares several highlights in his own education (he began with the goal of becoming a psychoanalyst) that parallel the growth of neuroscience and cognitive psychology.

For instance, I learned about Santiago Ramon y Cajal, who began as a painter but whose study of anatomy led him eventually to study the anatomy of the brain. According to Kandel, Cajal was the first scientist to figure out that what had been called “processes” in the brain were the axons and dendrites of the neuron — in other words, that neurons were in fact a highly specialized type of cell. This led to Cajal’s three principles:

  • The neuron is the fundamental structural and functional element of the brain — “both the basic building block and the elementary signaling unit.”
  • The terminals of one nerve’s axon communicate with the dendrites of another nerve only as specialized sites — which were later named synapses (from a Greek work meaning “to bind together”).
  • Neurons do not form connections indiscriminately; each sell links in specific pathways with others, and signals travel along these circuits in a predicatable pattern.

Later, Brenda Milner, especially in studying a man who’d had most of his temporal lobe and his hippocampus removed, developed additional principles. They’re obvious to us now, but in the mid-20th century, they weren’t:

  • Memory is a distinct mental function, separate from other perceptual, motor, and cognitive abilities.
  • Short-term memory and long-term memory can be stored separately. (E.g., loss of substance in the medial temporal lobe and the hippocampus disrupts the ability to convert short-term memory to long-term. Milner worked with her patient monthly for nearly thirty years. “Each time she entered the room and greeted him, he failed to recognize her.”)
  • At least one type of memory can be traced to specific places in the brain.

AplysiaKandel also describes his decision to try and understand learning through studying the sea slug Aplysia californica, which measures about a foot long. It has a relatively small brain (20,000 cells, compared with 100 billion in humans). The cells are grouped in clusters called ganglia, and each ganglion appeared responsible for certain reflexes. In addition, some of Aplysia’s nerve cells are fifty times larger than mammalian cells.

I’m always impressed (and often daunted) by the sheer amount of work in research like this. Kandel began studying Aplysia in the early 1960s, slowing them for a time while working as an instruction at the Massachusetts Mental Health Center, then moving to New York in 1965.

“…by 1969 Kupfermann [a colleague] and I had succeeded in identifying most of the nerve cells that make up the gill-withdrawal reflex.” This was the center of his study: his team worked at conditioning of this reflex. They found that stimulating any one point on Aplysia’s skin would activate only six of its 24 sensory neurons, which in turn would trigger 6 specific motor neurons.

A lot of detail, but for me a fascinating look at the foundations, or maybe even the subsoil, on which we’ve built the edifice of our knowledge.