Characterization of nonlinear spatiotemporal properties of macaque retinal ganglion cells using spike-triggered covariance

J W Pillow, E P Simoncelli and E J Chichilnisky

Published in Annual Meeting, Neuroscience, Nov 2003.
Light responses of retinal ganglion cells (RGCs) exhibit several kinds of nonlinearity. These nonlinearities have usually been probed with restricted sets of stimuli that do not provide a complete characterization of (a) the spatial and temporal structure of the nonlinearities and (b) neural response as a function of the stimulus. We developed a spike-triggered covariance (STC) analysis to provide such a characterization of primate RGC light responses.

Multi-electrode recordings from macaque RGCs were obtained from isolated retinas stimulated with one-dimensional spatiotemporal white noise (i.e. flickering bars). Spike-triggered average (STA) analysis revealed center-surround spatial organization and biphasic temporal integration expected from RGCs. Eigenvector analysis of the STC revealed components with spatial and temporal structure distinct from the STA. Excitatory STC components exhibited temporal structure similar to the STA, but finer spatial structure, consistent with input from multiple spatial subunits combined nonlinearly. Suppressive STC components exhibited spatial structure similar to the STA or to excitatory STC components, but temporal structure that was time-delayed relative to the STA, consistent with spike generation or contrast gain control nonlinearities.

A model consisting of spatially shifted subunits with a simple rectifying nonlinearity, summed and followed by leaky integrate-and-fire spike generation, accurately reproduced the observed STA, contrast-response function, and detailed spatial and temporal structure of STC components. These results suggest that spatial and temporal properties of nonlinearities in macaque RGC light response can be identified and characterized accurately using STC analysis.

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