Visually-guided correction of hand reaching movements: The neurophysiological bases in the cerebral cortex.

The ability of human and non-human primates to make fast corrections to hand movement trajectories after a sudden shift in the target's location is a key feature of visuo-motor behavior. In healthy individuals, hand movements smoothly adapt to a change in target location without needing to complete the movement to the first target location, as typical of parietal patients. This finding indicates that the nervous system continuously monitors the visual scene and is able to integrate new information in order to produce an efficient motor response. In this paper, we review the kinematics, reaction times and muscle activity observed during the online correction of hand movements as well as the underlying neurophysiological processes studied through single-cell neural recordings in monkeys. Brain stimulation, lesion and imaging studies in humans are also discussed. We demonstrate that while online correction mechanisms strongly depend on the activity of a parieto-frontal network of which the posterior parietal cortex is a crucial node, these mechanisms proceed smoothly and are similar to what is observed during simple point-to-point movements. Online correction of hand movements would rely on feedforward and feedback mechanisms in the parietal cortex, as part of the activity within the fronto-parietal network for the planning and execution of visuo-motor tasks.