Regional hippocampal lesions alter matching by monkeys: an anorexiant effect

Findings showed that monkeys with middle, but not anterior or posterior hippocampal damage, are impaired in ability to acquire matching-to-sample, if training is conducted without error correction. All groups except this middle hippocampal lesion group abandoned the spatial strategy and achieved above-chance levels of matching within 6,000 trials. Although monkeys with anterior and posterior hippocampal lesions abandoned spatial strategies of responding at the normal rate, they, along with the middle hippocampal lesion group began to show a short-session-effect which coincided with just-above-chance matching performance. Affected monkeys, although able to correctly match, would not consume the food pellet reward, showed signs of anxiety, and performed only 25 of the usual 200 problems offered each day. None of the surgical control or unoperated control monkeys exhibited the short-session-effect. The untreated short-session-effect continued for as long as two months, but was always quickly alleviated by oxazepam, diazepam, or chlordazepoxide hydrochloride.