HIPPOCAMPAL-LESIONS AND THE GENERALIZATION OF AUDITORY-STIMULI

Hippocampal ablation and control surgery were interposed in a standard discrimination training and generalization testing paradigm. Rats were trained in a bar-press situation to discriminate between two tones. Response during the presence of the S + (2150 Hz) tone was reinforced, while no reinforcement was given to response in the presence of the S- (550 Hz) tone. Training was continued until the ratio of S+ responses to S- equalled at least 9/1 for three consecutive days. Half the animals then sustained bilateral electrolytic hippocampal lesions; and half underwent craniotomy only. Following surgery, generalization testing revealed a decreased slope in the generalization gradient for the hippocampectomized group. This reflected the inability of hippocampally lesioned animals to withhold response to the S- and surrounding tones. These findings were interpreted as supporting the idea that the hippocampus plays a role in the inhibition of response to nonreinforced stimuli by gating the afferent transmission of such stimuli. © 1979.