In fact, there were questions it was possible to ask. For instance, under what circumstances does psychoanalysis work better than a placebo? Does it work better than other kinds of therapy? Who are the best therapists for what kinds of patients?

Talk about your Nobel research on the biology of memory.

I’ve long been interested in memory. What does it look like on a physical level? When I was a very young man, my mentor Harry Grundfest said, “Look, if you want to understand the brain you’re going to have to take a reductionist approach, one cell at a time.” He was so right.

So what’s the biggest problem in psychoanalysis? It’s memory! In the late 1950s, I and a colleague, Alden Spencer, had a very significant finding when we recorded the signals a hippocampus nerve cell puts out when it communicates with other cells. A psychologist named Brenda Milner had just shown that complex memory involves the hippocampus part of the brain, which is why we picked that type of cell to study. We were able to stimulate the various pathways coming into the cell and record the synaptic input. We saw how the hippocampus cell worked, but alas, that didn’t give insight into memory.

So in the 1960s, we went to a more reductionist approach. Instead of studying complicated mammalian brain cells, we studied the neural system of a simple animal — Aplysia, a snail with a very large nerve cell. We subjected them to learning and reflex tests similar to those that Pavlov had done. We’d stimulate the animals and see what kind of reflexes were produced, and then we tested them. We discovered that the snail’s reflexes could be modified by several forms of learning, and that learning involved alterations in how nerve cells communicated with one another.

We next looked at short- and long-term memory in the snail. I began to see what happens when you convert short-term memories to long-term ones. It would turn out that short-term memory involves transient changes of the connections between the cells. There is no anatomical change. Long-term memory involves enduring changes that result from the growth of new synaptic connections.

Did this surprise you?

It was astonishing! You could double the number of synaptic connections in a very simple neurocircuit as a result of experience and learning. The reason for that was that long-term memory alters the expression of genes in nerve cells, which is the cause of the growth of new synaptic connections. When you see that at the cellular level, you realize that the brain can change because of experience. It gives you a different feeling about how nature and nurture interact. They are not separate processes.

As neuroscience moves forward, there are all kinds of new possibilities emerging. There are people who are experimenting with ways to erase unpleasant memories. Do you approve?