LESIONS OF THE ENTORHINAL CORTEX DISRUPT BEHAVIORAL AND NEURONAL RESPONSES TO CONTEXT CHANGE DURING EXTINCTION OF DISCRIMINATIVE AVOIDANCE-BEHAVIOR

Rabbits given either electrolytic lesions of the entorhinal cortex or sham-lesions were trained to prevent a foot-shock by stepping in an ac tivity wheel after one tone, a positive conditioned stimulus (CS+), an d to ignore a different tone, a negative conditioned stimulus (CS-). N euronal activity was recorded simultaneously in the basolateral nucleu s of the amygdala, the CA1 cell field of hippocampus, anterior cingula te cortical area 24b and posterior cingulate cortical area 29c/d. The activity of neurons in the entorhinal cortex was recorded in the contr ols. Acquisition of conditioned avoidance responses (CRs) was not affe cted by lesions of the entorhinal cortex. Discriminative neuronal acti vity (greater neuronal responses to the CS+ than to the CS-) during CR acquisition was significantly enhanced in hippocampal area CA1 and at tenuated in the basolateral amygdala in rabbits with lesions. Followin g acquisition to a criterion, two counterbalanced extinction tests wer e administered, one in the original context and the other in the prese nce of novel contextual stimuli. CR frequency was significantly reduce d in controls but not in rabbits with lesions, during extinction with novel contextual stimuli, relative to performance in the original cont ext. The rabbits with lesions also showed fewer inter-trial responses than controls during extinction in the original context but intertrial response frequency in rabbits with lesions did not differ from the fr equency in controls during extinction in the novel context. Neurons in the basolateral amygdala in controls showed discriminative activity d uring extinction in the original context but not in the novel context. Amygdalar neurons in the rabbits with lesions did not show discrimina tive activity during extinction in either context. Posterior cingulate cortical neurons in control rabbits did not show discriminative activ ity during extinction in the original context but these neurons exhibi ted robust discriminative activity in the novel context. Posterior cin gulate cortical neurons in rabbits with lesions showed discriminative activity in both extinction sessions. The results indicated that the e ntorhinal cortex does not play a significant role in the acquisition o f discriminative avoidance behavior, under the employed conditions of training. However, the interactions of neurons in the entorhinal corte x, amygdala and cingulate cortex are essential for contextual modulati on of CRs during extinction.