Retrosplenial cortex lesions impair acquisition of active avoidance while sparing fear-based emotional memory

Abstract

There is strong evidence that the rat retrosplenial cortex (RC) is implicated in spatial navigation and in learning of both aversive and reward-based discrimination tasks. However, its involvement in other functions subserved by the limbic system to which it belongs has not yet been documented. We compared the performance of rats with bilateral excitotoxic damage to RC with that of control rats in a battery of conventional tests, including an open field, plus maze, fear conditioning, step-through passive avoidance, and two-way active avoidance techniques. In the open field, RC-lesioned rats showed somewhat decreased locomotion in the inner zone and increased defecation, which is suggestive of an anxiogenic effect. However, no differences between groups were detected in the plus-maze and inhibitory avoidance tests. Freezing scores recorded during fear conditioning, as well as during the context and tone tests, which were performed, respectively, 24 and 48 h after conditioning, did not differ between the groups. In contrast, acquisition of the active avoidance response was significantly impaired in rats with damaged RC, regarding both response latency and correctness. These data suggest that although the rat RC may play a role in the regulation of emotional responsiveness to new situations, it does not appear to contribute to emotional memory. They are also consistent with the idea that RC is a part of the limbic system that is involved in the compilation of motor programs for complex stereotyped movements such as approach and avoidance.