Alden [Spencer] was a mammalian chauvinist. He would never leave the mammalian nervous system, so he kept on looking for a simple system within the mammalian brain. And he ultimately focused in on the spinal cord. There were various things you could study [such as] reflex habituation, [dishabituation] etc. And he thought he would study that.

I was influenced by Grundfest and the crayfish and, you know, squid, and what [could be learned] from them. I was looking for an even simpler system. I wanted a radical reductionist approach to learning. Now many people thought this was crazy in those days because they thought even though reductionist approach worked in many areas of biology, it wouldn’t work for behavior that’s uniquely, you know, a mammalian, human phenomenon. I thought, that’s silly. In all the anthologies described you can see very interesting forms of learning and memory in simple animals. Not only that, at Harvard I’d read some Skinner and I now read up more on this. People had described simple learning paradigms, habituation, sensitization, classical conditioning that you could see in all animals. So I began to look for a simple system, and one thing about NIH [National Institutes of Health], everybody comes through. It was the mecca of neuroscience in those days.

So I went to seminars about worms, about flies, about all kinds of animals. And what caught my attention was the marine snail Aplysia. Now what’s so wonderful about the marine snail Aplysia? It met all the criteria that I thought were important. It had a limited number of nerve cells, the whole nervous system was only 20,000 nerve cells. Your brain and mine is a million million nerve cells. Number one. Number two, the cells, many of them were gigantic. Before I became presbyopic, I could see them with my naked eye. One of the cells is a millimeter in diameter.

Moreover, Arvanitaki had already described it, but it became clear to me this was very likely. Many of these cells are uniquely identifiable so you could return to the same cell time and time again, so it seemed to me this was an ideal thing to work.