Visual control of hand-reaching movement: activity in parietal area 7m.

The activity of single neurons was studied in parietal area 7m while monkeys performed an instructed-delay reaching task to visual targets under normal light conditions and in darkness. The task was aimed at assessing the influence of vision of hand position on the neural activity of 7m related either to static posture and movement of the hand or to eye position in the orbit. The results show the existence of preparatory, movement-related and postural activity for the control of reaching, all of which are strongly modulated by vision. The activity of many 7m neurons, otherwise insensitive to pure visual stimuli, seems to reflect complex interactions between gaze angle and hand position in the visual field.

Combination of hand and gaze signals during reaching: activity in parietal area 7 m of the monkey.

The role of area 7 m has been studied by recording the activity of single neurons of monkeys trained to fixate and reach toward peripheral targets. The target was randomly selected from eight possible locations on a virtual circle, of radius 30 degrees visual angle from a central target. Three tasks were employed to dissociate hand- from eye-related contributions. In the first task, animals looked and reached to the peripheral target. In a second task, the animal reached to the peripheral target while maintaining fixation on the central target. In the third task, the monkey maintained fixation on peripheral targets that were spatially coincident with those of the reaching tasks. The results show that cell activity in area 7 m relates, for some cells to eye position, for others to hand position and movement, and for the majority of cells to a combination of visuomanual and oculomotor information. This area, therefore, seems to perform an early combination of information in the processing leading from target localization to movement generation.