THE NUCLEUS-ACCUMBENS IN MONKEYS (MACACA-FASCICULARIS) .1. THE ORGANIZATION OF BEHAVIOR

A behavioural comparison was made between six unoperated control monke ys and six monkeys which received bilateral ibotenic acid lesions of t he nucleus accumbens. Two of the control monkeys were subsequently giv en bilateral lesions of the anterior cingulate and medial frontal cort ex (areas 24, 25 and 32) and were rested on the behavioural tasks. The NA lesioned monkeys, but not the anterior cingulate lesioned monkeys, were significantly impaired on a hoarding task in which they were req uired to remove 18 peanuts from their shells and store them in their c heek pouches. These same monkeys were not impaired when the nuts were presented without shells. Evidence is provided which suggests that thi s deficit is not motivational or due to gross motor impairments. A sec ond task in which the animals were required to search through four box es to retrieve food revealed a decrease in the tendency for the NA and cingulate lesioned animals to use an organized pattern of searching. Both groups were found to return to a previously opened box more often than controls. However, neither group showed signs of perseverative b ehaviour. Data from a ten-box version of this task suggest that these return errors were not due to a decrease in working memory. Together t hese studies suggest that both the NA and the anterior cingulate corte x contribute to the ability to organize behaviour temporally and spati ally.