DISCRIMINATIVE AND NONDISCRIMINATIVE CONTEXTUAL FEAR CONDITIONING POTENTIATE THE ACOUSTIC STARTLE RESPONSE

The acoustic startle reflex, a short-latency motor response to a loud noise, is modifiable by experience. Here we test whether contextual fe ar conditioning potentiates startle responses, in addition to two othe r indices of fear: freezing and defecation. First, we trained rats wit h zero, one or three 0.6-mA footshocks. Upon reexposure to the same co ntext, startle responses, amount of time freezing, and defecation were increased in the one- and three-shock groups, but not in the zero-sho ck group, compared with pretraining baseline levels. Second, to test w hether these increases in fear responses were context specific, we tra ined and tested rats in a context discrimination paradigm. Rats were t rained to discriminate between two contexts, one in which three footsh ocks where delivered, the other in which no footshocks were delivered. Startle amplitudes and time spent freezing were increased in the pair ed as opposed to the unpaired context. These results suggest that the acoustic startle reflex can be modified by a specific memory of an env ironmental context in which an aversive event has occurred.