Effects of Hippocampal, Amygdala, Hypothalamic and Parietal Lesions on a Classically Conditioned Fear Response

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Abstract
Experiments investigating the effects of limbic system lesions in a modified classical conditioning situation were performed on 68 rats. Pre- and post-operative tests were given to parietal and amygdalectomized Ss. Postoperative tests were given to parietal, hippocampal, and amygdalectomized Ss. Hypothalamic and amygdaloid Ss showed no evidence of learning the test response. Contrary to previous reports, it was found that animals with small hippocampal lesions were able to learn the test response. The observed learning deficits were discussed in terms of possible receptor mechanisms for painful stimuli controlled by basolateral amygdaloid nucleus and ventromedial hypothalamus.