Posttrial hippocampal, amygdaloid, and lateral hypothalamic electrical stimulation: effects on short- and long-term memory of an appetitive experience.

Water-deprived rats were given 150 licks of a 10% sucrose solution, followed 4 sec later by 30 sec of low-intensity electrical brain stimulation applied through bipolar electrodes implanted bilaterally in the dorsal hippocampus, amygdala, or lateral hypothalamus. Retention of the licking experience was then tested either 90 sec or 24 hr after the 150-lick experience by measuring the number of licks taken on an empty drinking tube. Rats that received hippocampal stimulation licked the empty tube less than controls did during the 24-hr, but not during the 90-sec, retention test. These data suggest that the hippocampus may be critically involved in processes (e.g., consolidation) mediating long-term, but not short-term, memory. Compared with controls, rats that received amygdala stimulation did not exhibit any changes in licking at either retention test. Rats that received lateral hypothalamic stimulation showed more licking compared with controls during the 90-sec, but not the 24-hr, retention test. Subsequent tests suggested that facilitation of short-term memory may have been influenced by stimulation-induced motivational changes.