Nonlinear measurement and classification of receptive fields in cat retinal ganglion cells

Originally, modeling of ganglion-cell responses in cat was based mainly on linear analysis. This is satisfactory for those cells in which spatial summation of excitation is approximately linear (X-cells) but it fails for Y-cells, where summation has strong nonlinear components. Others have shown the utility of using sinusoidal analysis to study harmonic and intermodulation nonlinearities in the temporal frequency domain. We have used Wiener-kernel analysis to obtain directly both temporal and spatial impulse responses and their nonlinear interactions. From these, we were able to predict accurately the responses that a counterphase modulated grating elicited in both X-cells and Y-cells. In addition, we show that the first-order responses can measure the two-dimensional spatial features of the receptive field with high resolution. Thus, nonlinear analysis of responses to white-noise stimuli may be sufficient to both classify and measure the receptive fields of many different types of ganglion cells.