Early coding of reaching: frontal and parietal association connections of parieto-occipital cortex

The ipsilateral association connections of the cortex of the dorsal part of the rostral bank of the parieto-occipital sulcus and of the adjoining post erior part of the superior parietal lobule were studied by using different retrograde flourescent 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 inje ction 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 intrapa rietal) and PEa, and, to a lesser extent, to frontal areas PMdr (rostral do rsal premotor cortex, F7) and PMdc (F2). All these areas project to that pa rt of the dorsocaudal premotor cortex that has a direct access to primary m otor cortex. V6A is also connected to area F5 and, to a lesser extent, to 7 a, ventral (VIP) and lateral (LIP) intraparietal areas. This pattern of ass ociation connections may explain the presence of visually-related and eye-p osition signals in premotor cortex, as well as the influence of information concerning arm position and movement direction on V6A neural activity. Are a V6A emerges as a potential 'early' node of the distributed network underl ying visually-guided reaching. In this network, reciprocal association conn ections probably impose, through re-entrant signalling, a recursive propert y to the operations leading to the composition of eye and hand motor comman ds.