Hippocampal stimulation and memory: effects of stimulation parameters and reinforcement magnitude

The present study investigated the extent to which post-conditioning stimulation-induced hippocampal seizure activity is a necessary condition for the production of retrograde amnesia in rats. Groups of animals received dorsal hippocampal stimulation at several different current intensities immediately following one-trial passive avoidance conditioning. The results suggest that current intensities far in excess of those which produce hippocampal seizure activity are a necessary condition for the production of retrograde amnesia. Reinforcement magnitude is not a significant variable at hippocampal seizure threshold current intensities. Current intensities insufficient for the production of retrograde amnesia, but sufficient for the production of dorsal hippocampal seizure activity, produced a spread of seizure activity into the ventral hippocampal formation. The results suggest that caution be exercised in attributing a role to the hippocampus in memory consolidation processes in the rat.