In Search of Memory: The Emergence of a New Science of Mind

by Eric R. Kandel

The synaptic potential between the sensory and motor neurons lasts only milliseconds, yet we had observed that a shock to Aplysia’s tail enhances glutamate release and synaptic transmission for many minutes. How does this come about? As my colleagues and I focused on the question, we noticed something curious. The strengthening of the synaptic connection between the sensory and motor neuron is accompanied by a very slow synaptic potential in the sensory cell, one that lasts for minutes rather than the milliseconds typical of synaptic potentials in the motor neuron. We soon found that the shock to Aplysia’s tail activates a second class of sensory neurons, one that receives information from the tail. These tail sensory neurons activate a group of interneurons that acts on the sensory neuron from the siphon. It is these interneurons that produce the remarkably slow synaptic potential. We then asked ourselves: What neurotransmitter do the interneurons release? How does this second neurotransmitter lead to the release of more glutamate from the terminals of the sensory neuron, thus creating short-term memory storage?