THE NUCLEUS-ACCUMBENS IN MONKEYS (MACACA-FASCICULARIS) .2. EMOTION AND MOTIVATION

Changes in incentive and emotion have been demonstrated in monkeys wit h amygdala lesions and monkeys with cingulate and medial frontal lesio ns. The nucleus accumbens (NA) receives inputs from the amygdala, hipp ocampus and anterior cingulate cortex. In order to better understand t he role of the NA and anterior cingulate cortex in processing emotiona l and motivational stimuli, studies were undertaken which compared the emotional and motivational behaviour of monkeys with NA lesions or an terior cingulate lesions with previous studies on amygdala-lesioned mo nkeys. A food preference task, a food vs. non-food discrimination task , and an approach-avoidance task were used with monkeys which received lesions of the NA or lesions of the anterior cingulate and medial fro ntal cortex. These tasks had previously been used to examine the emoti onal response of monkeys with amygdala lesions. In addition, the lesio ned monkeys were tested on a frustration task and a button press acqui sition-extinction task. Unlike amygdala-lesioned monkeys (Aggleton, J. P. and Passingham, R.E., J. Comp. Physiol. Psychol., 96 (1981) 961-977 and 96 (1982) 71-77), the NA-lesioned monkeys maintained normal food preferences, did not show signs of hyperorality in the food vs. non-fo od task, and performed normally on the approach-avoidance tasks. The N A-lesioned monkeys did, however, show an increase in activity, and vio lent and aggressive behaviour in response to stress in both the frustr ation task and the button press extinction task. In addition, the NA-l esioned monkeys performed normally during a button press acquisition t ask, but extinguished faster on a button press extinction task than th e control monkeys. The anterior cingulate-lesioned monkeys were also f ound to exhibit an increased responsiveness to frustration. Results of the food preference, food vs. non-food discrimination, and approach-a voidance tasks were similar to those obtained with NA lesions. These s tudies suggest that lesions of the NA or the anterior cingulate cortex result in substantial changes in emotional behavior, however, these c hanges do not mimic those found following lesions of the amygdala.