EFFECTS OF AMYGDALA, HIPPOCAMPUS, AND PERIAQUEDUCTAL GRAY LESIONS ON SHORT-TERM AND LONG-TERM CONTEXTUAL FEAR

The effects of amygdala, hippocampus, and periaqueductal gray (PAG) le sions on contextual fear conditioning in rats were examined. Freezing behavior served as the measure of conditioning. Unlesioned control ani mals showed reliable conditional freezing in the testing chamber when observed both immediately and 24 hr after footshocks. In contrast, rat s with amygdala or ventral PAG lesions exhibited a significant attenua tion in freezing both immediately and 24 hr after the shocks. Dorsal P AG lesions had no effect on freezing at either time. Animals with hipp ocampal lesions displayed robust freezing behavior immediately followi ng the shock, even though they showed a marked deficit in freezing 24 hr after the shock. These results indicate that there are anatomically dissociable short- and long-term conditional fear states.