Potentiated Startle: Its Relation to Freezing and Shock Intensity in Rats

Abstract

Acoustic startle response and freezing were measured in a potentiated startle paradigm in which a startle stimulus was presented either alone or in the presence of a light conditioned stimulus (CS) which had been paired previously with either 1-mA or 3-mA footshock. During the CS the 1-mA group had higher startle amplitudes and a higher percentage of freezing than the 3-mA group. Startle amplitude was positively correlated with freezing under all conditions. The nonmonotonic relation between potentiated startle and shock intensity replicated Davis and Astrachan's (1978) study. However, rather than suppressing startle, as they suggested, freezing facilitated startle and, like startle amplitude, was nonmonotonically related to shock intensity. Experiment 2 replicated these results and showed a regularly decreasing monotonic extinction function for potentiated startle and shock-associated freezing for both shock-level groups. Brown, Kalish, and Farber (1951) reported that the magnitude of the acoustic startle response was increased when the startle-eliciting stimulus was presented in conjunction with a stimulus previously paired with shock. This phenomenon, now commonly called the potentiated startle effect, has been frequently