Impaired retention of visual discriminated escape training produced by subseizure amygdala stimulation

These experiments examined the effects on memory of posttrial, subseizure, electrical stimulation of the amygdala. Rats were trained in a visual discriminated avoidance Y-maze. Each animal received 6 tirals on the training day. Retention, tested the following day, was measured both by the number of correct choices on the first 6 retraining trials and by the number of trials to a criterion of 5 of 6 correct choices. If administered 2 min, 1 h, or 4 h, but not 10 h, after training, bilateral amygdala stimulation significantly impaired retention as measured 24 h after training. In a second experiment, rats received unilateral amygdala stimulation in order to examine better the anatomical localization of effective stimulation sites. The unilateral stimulation was administered either 2 min, 10 min, 1 h, or 4 h after training. The behavioral procedures were the same as those used in the first experiment. For animals stimulated 2 min after training, the optimal stimulation region was one which extended rostrally from the ventrolateral portion of the basomedial nucleus to the dorsomedial region of the amygdala near the stria terminalis and nucleus centralis. For animals stimulated after a 10 min training-treatment interval, this amygdala region was not an effective stimulation site. However, in these animals, stimulation of the basolateral nucleus impaired later retention. Unilateral, posttraining amygdala stimulation administered 1 or 4 h after training did not appear to produce retention deficits. The findings of these experiments thus indicate that posttrial unilateral or bilateral amygdala stimulation impairs retention of discriminated avoidance training. Furthermore, the specific amygdala site at which posttrial stimulation impairs later retention varies with the training-treatment interval.