THE NUCLEUS-ACCUMBENS IN MONKEYS (MACACA-FASCICULARIS) .3. REVERSAL-LEARNING

The nucleus accumbens (NA), which receives inputs from limbic structur es and projects to the motor system, may be important for the associat ion of reinforcement with action. There are projections to the NA from the amygdala and hippocampus. Discrimination and reversal learning ta sks which are known to be disrupted by lesions to these areas in monke ys were given to monkeys with lesions of the NA. Twelve monkeys (Macac a fascicularis) were used in the present study. Six of these received ibotenic acid lesions which resulted in considerable cell loss in the NA; the remaining six acted as controls. The first group of six monkey s were taught a visual discrimination task pre-operatively. Post-opera tively, these monkeys were tested on visual and spatial discrimination and reversal tasks. A second group of sis monkeys were tested on a mo tor reversal task. The results indicate that ibotenic acid lesions of the NA transiently impair spatial but not visual reversal learning in monkeys. The NA lesions did not impair a monkey's ability to perform v isual or spatial discriminations, or the ability to perform the motor learning or motor reversal tasks. Our results suggest that bilateral l esions of the NA in monkeys do not disrupt the ability to discriminate basic properties of reward-related stimuli or the formation of visual stimulus-reward associations. In addition, our results argue against theories which suggest that the NA is important for behavioural switch ing or general behavioural flexibility. We conclude that the NA may pl ay a more specific role in the association of temporal and spatial cue s with movement and reward.