Effects of additional cues on passive avoidance learning and extinction in rats with hippocampal lesions

Following the acquisition of a water-rewarded approach response in a straight runway, the effects of introducing shock in the goal box (passive avoidance - PA) or withdrawing reinforcement (extinction) were compared in hippocampal, cortical, and operated control groups of rats. Under standard test conditions, hippocampal groups were impaired in PA learning and showed strong resistance to extinction, relative to the control groups. When additional cues were provided such that external stimuli associated with goal box events could be easily detected early in the runway, performance differences between the hippocampal and control groups were eliminated in the PA test and significantly reduced in extinction. The results emphasize the inefficient processing by hippocampally-damaged animals of stimulus cues following a shift in experimental contingencies.