Abstract
Area V6A occupies the caudalmost part of the superior parietal lobule in both human and non-human primates. In macaques, V6A is a visuomotor area that represents large part of the visual field and the upper limbs. V6A cells are modulated by the direction and amplitude of arm movement, by wrist orientation and by grip type, indicating that this area is involved in the control of all phases of reach-to-grasp actions. V6A may act as a ‘state estimator’ whose output is used to adjust the motor plan in order to maintain consistency between the ongoing movement and the desired one. In humans, neuroimaging studies have revealed strong homologies with macaque showing that hV6A is involved in the visuomotor control of goal-directed hand movements. Since goal-directed behaviors crucially depend on the ability to flexibly adapt the motor plan in response to unexpected changes in target location, which in turn depends on the ability to shift attention to a new location, we checked whether shifts of spatial attention modulate V6A activity. Indeed, 1) some V6A cells discharged whenever the animal covertly directed its spotlight of attention towards particular parts of its field of view, 2) hV6A was activated by covert attentional shifts in attentional reorienting and 3) TMS over the hV6A did affect these attentional shifts. In addition, it was observed that a small lesion matching hV6A resulted in a shifting attention deficit, particularly intense when repeated shifts of spatial attention were required. Notably, a small cortical region that likely includes hV6A was found to be implicated in coding visual information in terms of egocentric coordinates, that is the same coordinates used to direct the spotlight of attention. We suggest that hV6A hosts an egocentric spatial map useful to direct the limbs in reach-to-grasp movements, particularly towards moving objects and during self-motion.