Stimulation of specific regions of brain in rats modifies retention for newly acquired and old habits.

Three experiments were designed to investigate some effects of low-level stimulation of the amygdaloid complex (AMYG) and the mesencephalic reticular formation (MRF). Experiment 1 used a tilt box to test for motivational and/or reinforcement effects and failed to demonstrate these effects with stimulation of either structure. Experiment 2 used a one-trial fear-conditioning task and revealed that stimulation of the AMYG disrupted retention when given immediately after training or, under some conditions, 4 days after training. In the same task, Experiment 3 showed that stimulation of the MRF enhanced retention when given immediately after training or, under some conditions, 4 days after training. These data indicate that under these conditions, modification of retention by low-level stimulation of specific brain structures is independent of the age of the memory. Some implications of this result are discussed.