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- M. Stimberg, K. Wimmer,
R. Martin, L. Schwabe, J. Mariño, J. Schummers, D. C. Lyon, M. Sur, and
K. Obermayer. The Operating Regime of Local Computations in Primary Visual
Cortex.
.
Cerebral cortex, 19(9):2166-2180, September 2009.
In V1, local circuitry depends on the position in the orientation
map: close to pinwheel centers recurrent inputs show variable orientation
preferences; within iso-orientation domains inputs are relatively uniformly
tuned. Physiological properties such as cell's membrane potentials, spike
outputs, and temporal characteristics change systematically with map
location. We investigate in a firing rate and a Hodgkin-Huxley network model
what constraints these tuning characteristics of V1 neurons impose on the
cortical operating regime. Systematically varying the strength of both
recurrent excitation and inhibition, we test a wide range of model classes
and find the likely models to account for the experimental observations. We
show that recent intracellular and extracellular recordings from cat V1
provide the strongest evidence for a regime where excitatory and inhibitory
recurrent inputs are balanced and dominate the feed-forward input. Our
results are robust against changes in model assumptions such as spatial
extent and strength of lateral inhibition. Intriguingly, the most likely
recurrent regime is in a region of parameter space where small changes have
large effects on the network dynamics, and it is close to a regime of
''runaway excitation``, where the network shows strong self-sustained
activity. This could make the cortical response particularly sensitive to
modulation.
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