Saccadic Inhibition is Initiated in the Retina

Abstract

Abstract: : Purpose:Our goal was to understand how neuronal interactions in the retina mediate suppression of ganglion cell output during saccades. Methods:We measured activity from ganglion cells in the light adapted flat mount rabbit retina. The retina was stimulated with saccades simulated by abrupt shifts in the position of movies of natural scenes. Spiking, excitatory input and inhibitory input were measured from each ganglion cell using the loose cell-attached and whole cell patch clamp technique. The ganglion cells were identified by confocal reconstruction after the measurements. Results:In many ganglion cell types spiking activity completely ceased during the presentation of artificial saccades generated by rapid scene shifts completed within 100 msec. This cessation of spiking appeared to be mediated by an inhibitory wave that counteracted excitation for a wide range of space-time characteristics of local illumination. The inhibitory wave was initiated by a broad field integration across the visual scene because it persisted even when light input to the measured ganglion cell was masked with 700-1000 micron disk. This "saccadic inhibition" had very rapid kinetics and could be blocked with the GABAA channel blocker SR-95531 and the sodium channel blocker TTX. The spatial tuning of the saccadic inhibition was broad ranging from checkerboard sizes of 50-500 microns. Conclusion:A robust component of saccadic suppression is mediated in the retina itself. Amacrine cells integrate global changes in the visual scene over regions greater than 1000 microns and propagate this activity via action potentials as feedforward inhibition to ganglion cells. Saccadic suppression in many ganglion cell types is absolute because this amacrine cell activity occurs fast enough to preclude generation of even the first spike that would have been generated by the ganglion cell.

Keywords: 415 ganglion cells • 312 amacrine cells • 394 electrophysiology: non-clinical