Neural activity was recorded in the parietooccipital cortex while monkeys performed different tasks aimed at investigating visuomotor interactions of retinal, eye, and arm-related signals on neural activity. The tasks were arm reaching 1) to foveated targets; 2) to extrafoveal targets, with constant eye position; 3) within an instructed-delayed paradigm, under both light and darkness; 4) saccadic eye movements toward, and static eye holding on peripheral targets; and 5) visual fixation and stimulation. The activity of many cells was modulated during arm reaction (68%) and movement time (58%), and during static holding of the arm in space (64%), when eye position was kept constant. Eye position influenced the activity of many cells during hand reaction (45%) and movement time (51%) and holding of hand static position (69%). Many cells (56%) were also modulated during preparation for hand movement, in the delayed reach task. Modulation was present also in the dark in 59% of cells during this epoch, 51% during reaction and movement time, and 48% during eye/hand holding on the target. Cells (50%) displaying light-dark differences of activity were considered as related to the sight and monitoring of hand motion and/or position in the visual field. Saccadic eye movements modulated a smaller percentage (25%) of cells than eye position (68%). Visual receptive fields were mapped in 44% of the cells studied. They were generally large and extended to the periphery of the tested (30 degrees ) visual field. Sixty-six percent of cells were motion sensitive. Therefore the activity of many neurons in this area reflects the combined influence of visual, eye, and arm movement-related signals. For most neurons, the orientation of the preferred directions computed across different epochs and tasks, therefore expression of all different eye- and hand-related activity types, clustered within a limited sector of space, the field of global tuning. These spatial fields might be an ideal frame to combine eye and hand signals, thanks to the congruence of their tuning properties. The relationships between cell activity and oculomotor and visuomanual behavior were task dependent. During saccades, most cells were recruited when the eye moved to a spatial location that was also target for hand movement, whereas during hand movement most cells fired depending on whether or not the animal had prior knowledge about the location of the visual targets.

The ipsilateral association connections of the cortex of the dorsal part of the rostral bank of the parieto-occipital sulcus and of the adjoining posterior part of the superior parietal lobule were studied by using different retrograde fluorescent tracers. Fluoro-Ruby, Fast blue and Diamidino yellow were injected into visual area V6A, and dorso-caudal (PMdc, F2) and dorso-rostral (PMdr, F7) premotor cortex, respectively. The parietal area of injection had been previously characterized physiologically in behaving monkeys, through a variety of oculomotor and visuomanual tasks. Area V6A is mainly linked by reciprocal projections to parietal areas 7m, MIP (medial intraparietal) and PEa, and, to a lesser extent, to frontal areas PMdr (rostral dorsal premotor cortex, F7) and PMdc (F2). All these areas project to that part of the dorsocaudal premotor cortex that has a direct access to primary motor cortex. V6A is also connected to area F5 and, to a lesser extent, to 7a, ventral (VIP) and lateral (LIP) intraparietal areas. This pattern of association connections may explain the presence of visually-related and eye-position signals in premotor cortex, as well as the influence of information concerning arm position and movement direction on V6A neural activity. Area V6A emerges as a potential 'early' node of the distributed network underlying visually-guided reaching. In this network, reciprocal association connections probably impose, through re-entrant signalling, a recursive property to the operations leading to the composition of eye and hand motor commands.

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