Effect of lesioning the nucleus accumbens on attentive preparation and performance of a reaching movement in the cat

The nucleus accumbens is often considered as an interface between limbic and motor brain structures. In the present experiment, we investigated the effect of a bilateral lesion of the nucleus accumbens on a motor task with attentional constraints. Four male cats were trained to reach for a mobile target that was only accessible for a short period of time and after a variable delay of expectation. They were food-rewarded. Their visuomotor performance was analyzed in speed and accuracy. Their ECoG was recorded to evaluate the occurrence of beta-rhythms that have been shown to be related to a behaviour of focalized attention. After stabilization of their visuomotor performance, all subjects underwent a bilateral neurotoxic lesion of the nucleus accumbens. After lesion, cats were able to maintain their focalized attention while waiting for the target for longer periods of time and the probability of beta-activity increased. Their visuomotor performance showed an improvement both in accuracy and in speed, Moreover, unexpected external stimuli were less efficient in diverting the cats' attention from their task, so that the proportion of unsuccessful trials due to inattention decreased after lesion. The data showed that the lesion induced a focalization of attention resulting in an improvement of motor performance. The role of the nucleus accumbens both in attention control and in modulating motor output is discussed together with the possible cerebral pathway involved.