Male Wistar rats were subjected to a
differential Pavlovian fear conditioning procedure
in which one of two tones (6 or 10 kHz)
was followed by an electric shock (CS+) and the
other was not (CS-). Before and after fear
conditioning, we recorded the evoked potentials
elicited by CS+ and CS- from electrodes aimed at
the lateral nucleus of the amygdala. Before
conditioning, a slow, negative component with
peak amplitude around 150 ms was present in
the evoked potentials. This component was
sensitive to habituation. After fear conditioning,
both CS+ and CS- elicited the same late
component, albeit with a larger amplitude. This
enhancement was temporary: decreasing
amplitude was observed in the course of CS test
presentations under extinction. Prior research
revealed a comparable slow component in the
amygdala of the cat under similar experimental
conditions. The collective results indicate that
the large late component in the amygdala is
enhanced by fear conditioning, suggesting that
such enhancement reflects the anticipation of a
biologically significant event.