The effects of fixed sequence of US intensities and CS-US correlation on licking suppression in rats

Abstract

Two experiments investigated the effects of shock (US) sequence and correlation between signals (CSs) and shocks (USs) on contextual fear with conditioned licking suppression preparation. In both experiments, three shocks of differentintensities were presented in fixed or random order. These shocks were correlated or uncorrelated with three different tones in Experiment 1, and with light, tone, and white noise in Experiment 2. In Experiment 1, the basal licking behavior was more suppressed in the groups with random shock sequence than in the groups with fixed shock sequence, regardless of combination of signals with shocks. Whereas in Experiment 2, the basal licking suppression was greater when signals and shocks were uncorrelated than when they were correlated, regardless of shock sequence. These results suggest that the factor to attenuate contextual fear assessed by licking suppression varies depending on the degree of distinctiveness among signals.