NONLINEAR DYNAMICS OF THE CENTER MECHANISM OF CAT RETINAL GANGLION CELLS.

The receptive-field organization of the cat X retinal ganglion cell is dominated by a small, excitatory center and a larger, inhibitory surround. Center and surround mechanisms are approximately linear, and to a first approximation, their signals combine by simple algebraic summation. However, a nonlinear neural mechanism, the contrast gain control, modulates retinal dynamics depending on local contrast. The qualitative effect of the contrast gain control is to tune the dynamics of ganglion cells to high temporal frequencies when nearby regions of the retina are stimulated by a pattern. A model is proposed which includes nonlinear feedback as a crucial feature. The model concisely explains responses to both broadband signals and step signals over a wide range of contrasts.