J. Pillow, 8/5/03
<br><br>

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

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.
<br><br>

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.
<br><br>

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.