title: The operating regime of local computations in primary visual cortex.
abstract: 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.
authors.affiliation: School of Computer Science and Electrical Engineering and Bernstein Center for Computational Neuroscience, Technische Universität Berlin, 10587 Berlin, Germany.
authors.forename: Marcel
authors.initials: M
authors.lastname: Stimberg
authors.forename: Klaus
authors.initials: K
authors.lastname: Wimmer
authors.forename: Robert
authors.initials: R
authors.lastname: Martin
authors.forename: Lars
authors.initials: L
authors.lastname: Schwabe
authors.forename: Jorge
authors.initials: J
authors.lastname: Mariño
authors.forename: James
authors.initials: J
authors.lastname: Schummers
authors.forename: David C
authors.initials: DC
authors.lastname: Lyon
authors.forename: Mriganka
authors.initials: M
authors.lastname: Sur
authors.forename: Klaus
authors.initials: K
authors.lastname: Obermayer
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D003071:Cognition / Q000502:physiology*; D003198:Computer Simulation; D005074:Evoked Potentials, Visual / Q000502:physiology*; D006801:Humans; D008959:Models, Neurological; D009415:Nerve Net / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*