Hippocampal activity during memory disruption of passive avoidance by electroconvulsive shock

Hippocampal activity was monitored during 1-trial passive avoidance learning of foot shock (FS) disrupted by electroconvulsive shock (ECS). Animals receiving FS showed synchronized activity concurrent with aversive responses and took significantly longer than FS-ECS subjects to descend from a platform 24 hrs. after experimental treatment. FS-ECS animals showed overt tonic-clonic seizures and hippocampal epileptiform activity followed by typical post-ictal behavioral and electrographic depression. On the retention trials, FS animals exhibited desynchronization concomitant with freezing behavior. No obvious difference in hippocampal activity between FS and FS-ECS animals was found that could be related to differences in retention; rather, such activity appeared to be related to momentary behavior patterns. It was suggested that hippocampus may function in initial stages of stimulas processing, resisting contamination of past experience.