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Spike timing precision and visual signaling in primate retinal
ganglion cells
Valerie J. Uzzell and E.J. Chichilnisky
University of California, San Diego
The Salk Institute
Recent findings indicate that retinal ganglion cell (RGC) spike trains in
salamander and rabbit can exhibit striking timing reproducibility (a few
ms) in response to repeated stimuli. How important is the precise timing
of RGC spikes for conveying the temporal structure of visual stimuli to
the brain? Using multi-electrode recordings from isolated retinas of
macaque monkeys, we have begun to determine how accurately time-varying
stimuli can be (a) classified or (b) reconstructed based on the timing of
spikes. In (a), spike trains elicited by a brief flash and by an
identical delayed flash were represented as vectors in a
multi-dimensional space and classified using linear discriminant
analysis. Classification performance was examined as a function of flash
delay to determine what delay was sufficient to reliably distinguish the
flashes. In (b), RGC spike trains were used to linearly reconstruct the
time course of a rapidly fluctuating white noise stimulus. Spike times
were then artificially jittered by a variable amount to determine how
reconstruction accuracy declined with reduced spike timing precision.
Temporal precision assessed using (a) tended to increase with contrast,
and tended to decrease with the integration time of the cell's light
response measured with reverse correlation, as would be predicted from
simple models of the light response. Preliminary results indicate that
some primate RGCs can reliably distinguish two flashes occurring 20-30 ms
apart. By this measure, the temporal precision of visual signaling by
RGCs may be coarser than has been proposed, at least in primate retina.
Preliminary results suggest that temporal precision assessed with method
(b) was comparable.