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

by Eric R. Kandel

These findings caused us to realize that there are two kinds of neural circuits important in behavior and learning: mediating circuits, which we had characterized earlier, and modulating circuits, which we were just beginning to characterize in detail (figure 16–1). Mediating circuits produce behavior directly and are therefore Kantian in nature. These are the genetically and developmentally determined neuronal components of the behavior, the neuronal architecture. The mediating circuit is made up of the sensory neurons that innervate the siphon, the interneurons, and the motor neurons that control the gill-withdrawal reflex. With learning, the mediating circuit becomes the student and acquires new knowledge. The modulating circuit is Lockean in nature; it serves as a teacher. It is not directly involved in producing a behavior but instead fine-tunes the behavior in response to learning by modulating—heterosynaptically—the strength of synaptic connections between the sensory and motor neurons. Activated