The influence of threshold variability on the response of visual cortical neurons

Abstract

Orientation–selective neurons in monkeys and cats show contrast saturation and contrast-invariant orientation tuning (Albrecht and Hamilton, J. Neurophysiol. 48 (1982) 217–237). Recently proposed models for orientation selectivity predict contrast invariant orientation tuning but no contrast saturation at high strength of intracortical recurrent couplings, whereas at lower coupling strengths the contrast response saturates but the tuning widths are contrast dependent (Hansel and Sompolinsky, Methods in Neuronal Modeling, MIT Press, Cambridge, MA, 1997, pp. 499–567; Stetter et al., Visual Neurosci., Submitted for publication). In the present work we address the question, if and under which conditions the incorporation of a stochastic distribution of activation thresholds for cortical neurons helps resolving that paradoxon. We find that both phenomena occurs naturally if two different classes of inhibitory inter-neurons are combined. Low-threshold inhibition keeps the gain of the cortical amplification finite, whereas high-threshold inhibition causes contrast saturation.