LINEAR AND NONLINEAR CONTRIBUTIONS TO STEP RESPONSES IN CAT RETINAL GANGLION-CELLS

We measured excitatory and inhibitory step responses of cat retinal ga nglion cells to square wave contrast reversal of stationary sinusoidal gratings. In most Y-cells the initial increase in firing rate (early peak) of the excitatory responses was followed by a distinct second in crease in firing rate (late peak). Analysis of the spatial frequency a nd spatial phase dependence of the two peaks indicated that the early peak appears to be produced by the spatially linear center mechanism, while the late peak appears to be produced by the rectifying subunits described by Hochstein and Shapley (1976) Journal of Physiology, Londo n, 262, 237-264, 265-284. These results indicate that the presence of two peaks in ganglion cell step responses is the result of two excitat ory inputs with different time courses, and that inhibitory inputs are not required to explain the appearance of these responses. Copyright (C) 1996. Published by Elsevier Science Ltd.