Communicative Pointing Ameliorates Grasping Deficitsafter an Inactivation and Lesions of the Ventral Premotor Cortex in Japanese Monkeys (Macaca fuscata)

Pointing is the most convenient communication in social interaction: its gesture is highly visible and is found in all cultures with the identical form. However, the brain mechanisms of communicative pointing are still unknown. The pointing is, from a psychological point of view, considered to develop from grasping attempt with help from others. Thus, we hypothesized that pointing deficits would appear after lesions of the ventral premotor cortex (PMv) that was fundamental to grasping, and examined whether the pointing would be influenced by the PMv lesions in monkeys. The PMv-lesioned subjects showed deficits in reaching and grasping, and those deficits were, contrary to our expectation, ameliorated through the pointing. A subject with muscimol injection to PMv required 4. 02 sec to obtain food but the time was reduced to 1. 19 sec after communicative pointing. Another subject rarely used one limb after bilateral PMv ablations, but became to grasp food with the hand after the training of communicative pointing. These results suggest that communicative pointing is useful to recover the grasping and reaching deficits induced by PMv lesions.