Disruption of rabbit (Oryctolagus cuniculus) nictitating membrane conditioning by posttrial electrical stimulation of hippocampus

Two experiments were conducted involving classical conditioning of the nictitating membrane response of rabbits with posttrial electrical brain stimulation. Hippocampal posttrial stimulation (PTS) presented immediately after each CS-US paired trial was found to cause massive disruption of conditioning by comparison with performance of either a cortical PTS group, an operated but unstimulated group, or an unoperated control group. The major effect of PTS was to postpone CR emergence. Once CRs began to occur, conditioning seemed to proceed normally regardless of the presence or absence of stimulation. Hippocampal PTS initiated after conditioning had no effect on the elicitation of conditioned responses. The results indicated that hippocampal PTS disrupted consolidation but did not affect either registration of stimuli or execution of unconditioned or conditioned responses. It was concluded that classical conditioning of the rabbit nictitating membrane response is an excellent model neural system for the investigation of neurophysiological aspects of memory.