Time-dependent post-trial changes in the localization of amnestic electrical stimulation sites within the amygdala in rats

This experiment examined the effects, on memory, of unilateral subseizure electrical stimulation of the amygdala. Rats were trained in a one-trial inhibitory (passive) avoidance task; retention performance was tested 24 hr after training. If administered either 30 sec or 10 min, but not 4 hr, after training, post-trial amygdala stimulation impaired later retention performance. However, histological examination of effective stimulation sites within the amygdala indicated that the specific electrode placements which effectively impaired later retention differed following stimulation at the 30-sec or 10- min training-treatment intervals. Electrical stimulation administered 30 sec after training impaired later retention in those animals which had electrodes terminating in an amygdala region, which included the basomedial nucleus and the dorsomedial portion of the amygdala. Stimulation of this area 10 min after training did not significantly impair later retention. However, after a 10-min training-stimulation interval, those animals which had electrodes terminating in the basolateral nucleus displayed impaired retention performance. Thus, the amygdala region in which post-trial electrical stimulation modulates later retention performance varies with time after training.