Inactivation of the ventral premotor cortex biases the laterality of motoric choices.

The visual, tactile, and motor properties of neurons in the ventral premotor cortex (PMv) suggest that the PMv plays an important role in the interaction of the face and upper extremities with visual objects, a function that might be disrupted by inactivation of the PMv. The behavior of three rhesus monkeys was, therefore, examined while the PMv was reversibly inactivated by intracortical injection of muscimol. Unilateral PMv inactivation produced no overt deficit in a monkey's ability to reach out and grasp a food morsel with either hand, nor did the monkey have difficulty in extracting a food morsel from a narrow well or in performing a visually cued individuated finger movement task. Unilateral PMv inactivation did bias the laterality of the monkeys' motoric choices, however. When two equivalent food morsels were presented simultaneously to the monkey's right and left, the likelihood that the monkey would make motoric responses contralateral to the inactivated PMv was reduced. After PMv muscimol injections, a monkey was less likely to initially turn its head contralaterally to inspect food morsels, less likely to reach for the food morsel with its contralateral hand, and less likely to take the morsel on its contralateral side. Catch trials in which a food morsel was present only on one side showed that the monkey was aware of the contralateral food morsels and was able to turn its head contralaterally and to use its contralateral arm and hand promptly and accurately. These observations suggest that, when equivalent visual objects for behavioral interaction are present bilaterally, the PMv plays a role in choosing the side to which motoric responses will be directed and the body part that will be deployed as the response effector.