Early discrimination of coherent versus incoherent motion by multiunit andsynaptic activity in human putative MT+

A laminar probe was chronically implanted in human putative MT+. The area w as specifically responsive to globally coherent visual motion, a crucial as pect of the perception of movement through space. The probe contained 23 mi crocontacts spaced every 175 mu in a linear array roughly perpendicular to the cortical surface. Current-source density (CSD) and multiunit activity ( MUA) were recorded while viewing initially stationary random dot patterns t hat either moved incoherently or dilated from the central fixation. Onset o f visual motion evoked large MUA/CSD activity, with coherent mo on evoking earlier and faster-rising MUA/CSD activity than incoherent, in both superfi cial and deep pyramidal layers. The selective response, peaking at approxim ate to 115 ms, was especially large in deep pyramids, providing evidence th at information necessary for visual flow calculations is projected from MT at an early latency to distant structures. The early onset of differential MUA/CSD implies that the selectivity of this area does not depend on recur rent inhibition or other intrinsic circuitry to detect coherent motion. The initially greater increase of MUA to coherent stimuli was followed by a gr eater decrease beginning at approximate to 133 ms, apparently because of re current inhibition. This resulted in the total MUA being greater to incoher ent than coherent stimuli, whereas total rectified CSD was overall greater to coherent than to incoherent stimuli. However, MUA distinguished stationa ry from moving stimuli more strongly than did CSD. Thus, while estimates of total cell firing (MUA), and of total synaptic activity (CSD) generally co rrespond to previously reported BOLD results, they may differ in important details. (C) 2001 Wiley-Liss, Inc.