Eye-hand coordination during reaching. I. Anatomical relationships betweenparietal and frontal cortex

The anatomical and physiological substrata of eye-hand coordination during reaching were studied through combined anatomical and physiological techniq ues. The association connections of parietal areas V6A and PEc. and those o f dorso-rostral (F7) and dorso-caudal (F2) premotor cortex were studied in monkeys, after physiological characterization of the parietal regions where retrograde tracers were injected. The results show that parieto-occipital area V6A is reciprocally connected with F7, and receives a smaller projecti on from F2, Local parietal projections to V6A arise from areas MIP and, to a lesser extent, 7m, PEa and PEc. On the contrary, parietal area PEc is str ongly and reciprocally connected with the part of F2 located close to the p re-central dimple (pre-CD). Local parietal projections to PEc come from a d istributed network, including PEa, MIF! PEci and, to a lesser extent, 7m, V 6A, 7a and MST. promotor area F7 receives parietal projections mainly from 7m and V6A, and local frontal projections mainly from F2. On the contrary, promotor area F2 in the pre-CD zone receives parietal inputs from PEc and, to a lesser extent, PEci, while in the peri-arcuate zone F2 receives pariet al projections from PEa and MIP Local frontal projections to F2 pre-CO most ly stem from F4, and, to a lesser extent, from F7 and F3, and CMAd; those a ddressed to peri-arcuate zone of F2 arise mainly from F5 and, to a lesser e xtent, from F7, F4, dorsal (CMAd) and ventral (CMAv) cingulate motor areas, pre-supplementary (F6) and supplementary (F3) motor areas. The distributio n of association cells in both frontal and parietal cortex was characterize d through a spectral analysis that revealed an arrangement of these cells i n the form of bands, composed of cell clusters, or 'columns', The reciproca l connections linking parietal and frontal cortex might explain the presenc e of visually related and eye-position signals in premotor cortex, as well as the influence of information about arm position and movement direction i n V6A and PEc. The association connections identified in this study might c arry sensory as well motor information that presumably provides a basis for a re-entrant signaling. This might be necessary to match retinal-, eye- an d hand-related information underlying eye-hand coordination during reaching .