Effects of hippocampal lesions on heart rate in aversive classical conditioning

Abstract

Groups of hippocampal-lesioned, neocortical-control and sham operated rats received shock on alternate trials during a 10-day classical conditioning period. Heart rate during prestimulus, stimulus and post-shock periods was evaluated. Hippocampal rats did not show prestimulus heart rate patterning resulting from the shock-no shock sequence of trials as did the other two groups. The tachycardic response to the stimulus, however, was the same in all groups. During 5 days of extinction, all groups showed a reduced response to the stimulus and the prestimulus rates for the 3 groups were equivalent. Since these findings were not accompanied by differences in heart rate response to the shock or in activity, it may be concluded that the effect of hippocampal lesions was to reduce the animal's sensitivity to the reinforcement schedule while not affecting heart rate response attenuation during extinction.