The collapse effect and delay of reinforcement with amygdalectomized rats

Abstract

In Phase 1, alleyway run speeds of amygdalectomized rats given large (12 pellets) or small (2 pellets) magnitude of reward were initially faster for the large-magnitude group, with the small-magnitude group catching up (termed the collapse effect) early in training. The collapse effect for nonlesion groups given similar magnitudes of reward occurred also, but much later in training. In Phase 2, all animals were given the same number of pellets as in Phase 1 with the addition of a 60-sec goalbox delay of reinforcement. In the lesion animals, the brief increase in performance, due to such a shift, occurred later in training than it did for the non-lesion animals. Following the brief increase there was a large decrement in responding for all groups, but the performance decrement of the lesion groups combined was less than it was for the nonlesion groups combined. Thus, rats with amygdala lesions were less responsive to original, and to changes in, contingencies of reinforcement relative to control animals. The normal function of the amygdala is briefly discussed.