A Neural Analysis of Fear Conditioning
Michael Davis Janice M. Hitchcock Jeffrey B. Rosen Ribicoff Research Facilities of the Connecticut Mental Health Center Yale University School of Medicine
A major challenge in neuroscience is to understand the biological substrates of learning and memory. Eventually this will involve a detailed cellular and biochemical description of the events in the nervous system that result in a relatively permanent change in neural transmission that allows a formerly neutral stimulus to produce or affect some behavioral response. The most definitive work on the cellular and biochemical analysis of learning and memory has been carried out in invertebrate nervous systems ( Alkon, 1979; Carew, 1984; Castellucci, Pinsker, Kupfermann, & Kandel, 1970; Crow & Alkon, 1980; Hawkins, Abrams, Carew, & Kandel, 1983, Walters & Byrne, 1985). A major advance in the analysis of these questions was to choose a simple reflex behavior that could be modified by experience and then determine the neural circuit that mediated the behavior being measured. Once this was done it was possible to isolate where different types of plasticity occurred and then determine how these changes were brought about at the cellular level.
Comparably detailed biochemical analyses of learning and memory that relate directly to behavioral output have not been possible in vertebrate nervous systems. In large part this is because it has been very difficult to isolate where plastic changes take place in complex vertebrate nervous systems. Thus at this stage it is important to develop simple models of learning and memory in complex vertebrates that can be used to isolate loci within the nervous system where plastic changes take place that allow a conditioned stimulus to induce or affect behavior. The short-latency acoustic startle reflex enhanced by prior classical fear conditioning may be an especially promising model system with which to carry out this type of analysis.