Subcortical mechanisms in emotional behavior: the effect of rhinencephalic injury upon the acquisition and retention of a conditioned avoidance response in cats.

Abstract

The present report describes an expt. investigating the acquisition and retention of a conditioned avoidance response in cats with surgical lesions largely limited to the amygdaloid nuclei. The avoidance response consisted of the cat''s passage through an open doorway separating the two compartments of a conventional "double-grill" box in response to the presentation of a 30-sec. conditioned clicker stimulus, thus terminating the clicker and preventing the shock which followed the failure to respond within the 30-sec. interval.(1). In Part I of the expt. (Acquisition), 28 adult stock cats were divided into 3 groups. Group I (10 animals) sustained bilateral lesions of the amygdaloid complex prior to avoidance training. Group II (3 animals) sustained lesions in the hippocampus (2 cats) or cingulate cortex (1 cat) prior to avoidance training. Group III (15 animals) was trained and served as unoperated controls. The avoidance response was established in all animals to a 90% criterion by successive daily postoperative sets of 30 trials each. The amygdalectomized animals (Group I) required significantly more training trials to reach criterion than either the operated (Group II) or unoperated (Group III) control animals. (2). In Part II of the expt. (Retention), 3 subgroups were formed from the unoperated control animals (Group III) of Part I of the expt. Subgroup A (3 animals) sustained bilateral lesions of the amygdaloid nuclei, and Subgroup B (3 animals) was subjected to bilateral lesions of the orbitofrontal cortex following acquisition of the avoidance response. Subgroup C (3 animals) served as unoperated controls. Postoperative tests in all 3 subgroups revealed no significant decrement in retention of the avoidance response in either the amygdalectomized cats (Subgroup A) or the unoperated control cats (Subgroup C). In contrast, cats with lesions of the orbitofrontal cortex (Subgroup B) showed no retention of the avoidance response even after 150 retraining trials. (3). Upon completion of the expts., the animals were sacrificed, and the lesions reconstructed histologically. (4). The implications of these findings for theoretical formulations of avoidance learning have been discussed.