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- J. Schummers, B. Cronin,
K. Wimmer, M. Stimberg, R. Martin, K. Obermayer, K. P. Koerding, and M. Sur.
Dynamics of orientation tuning in cat V1 neurons depend on location
within layers and orientation maps.
.
Frontiers in Neuroscience, 1:145-159, 2007.
(FTP PDF, 690 kb)
Analysis of the timecourse of the orientation tuning of responses
in primary visual cortex (V1) can provide insight into the circuitry
underlying tuning. Several studies have examined the temporal evolution of
orientation selectivity in V1 neurons, but there is no consensus regarding
the stability of orientation tuning properties over the timecourse of the
response. We have used reverse-correlation analysis of the responses to
dynamic grating stimuli to reexamine this issue in cat V1 neurons. We find
that the preferred orientation and tuning curve shape are stable in the
majority of neurons; however, more than forty percent of cells show a
significant change in either preferred orientation or tuning width between
early and late portions of the response. To examine the influence of the
local cortical circuit connectivity, we analyzed the timecourse of responses
as a function of receptive field type, laminar position and orientation map
position. Simple cells are more selective, and reach peak selectivity
earlier, than complex cells. There are pronounced laminar differences in the
timing of responses: middle layer cells respond faster, deep layer cells have
prolonged response decay, and superficial cells are intermediate in timing.
The average timing of neurons near and far from pinwheel centers is similar,
but there is more variability in the timecourse of responses near pinwheel
centers. This result was reproduced in an established network model of V1
operating in a regime of balanced excitatory and inhibitory recurrent
connections, confirming previous results. Thus, response dynamics of cortical
neurons reflect circuitry based on both vertical and horizontal location
within cortical networks.
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