Early Coding of Reaching in the Parietooccipital Cortex

1 Dipartimento di Fisiologia Umana e Farmacologia, Università di Roma `la Sapienza,' 00185 Rome; 2 Istituto di Ricovero e Cura a Carattere Scientifico Santa Lucia, 00179 Rome; and 3 Dipartimento di Neuroscienze, Università di Roma `Tor Vergata,' 00133 Rome, Italy Battaglia-Mayer, Alexandra, Stefano Ferraina, Takashi Mitsuda, Barbara Marconi, Aldo Genovesio, Paolo Onorati, Francesco Lacquaniti, and Roberto Caminiti. Early Coding of Reaching in the Parietooccipital Cortex. J. Neurophysiol. 83: 2374-2391, 2000. 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°) 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 mig