MEMORY DEFICITS FOLLOWING LESIONS OF HIPPOCAMPUS OR AMYGDALA IN RAT -ASSESSMENT BY AN OBJECT-MEMORY TEST BATTERY

We tested rats with bilateral lesions of the hippocampus or the amygda la on a battery of five object-memory tasks, which resemble those that have been used in the study of amnesia in humans and monkeys: (1) obj ect discrimination, (2) discrimination reversal, (3) eight-pair concur rent object discrimination, (4) nonrecurring-items delayed nonmatching -to-sample (DNMS) with retention delays of 4, 15, 30, 60, and 120 sec and with Lists of three, five, and seven samples, and (5) order discri mination. Ah testing was postsurgery. Relative to control rats, the ra ts with hippocampal lesions required more trials to master the object discrimination and the concurrent object discrimination. Rats with hip pocampal lesions required about as many trials as did control rats to master DNMS at the 4-sec delay and displayed only mild deficits at the longest (120-sec) delay. Rats with amygdalar lesions required more tr ials to master the concurrent object discriminations than did controls , but significantly fewer than did rats with hippocampal lesions. They required more trials than did controls to master DNMS with a 4-sec de lay; however, after they had done so, they continued to perform normal ly as the delay was increased. Neither lesion produced deficits on dis crimination reversal, DNMS with lists, or order discrimination. While these findings demonstrate that the mnemonic effects of hippocampal an d amygdalar lesions can be dissociated using a battery of object-memor y tasks, they also suggest a Limited role for these two structures in many object-memory abilities.