MATHEMATICAL BIOLOGY SEMINAR

        The mechanisms underlying the distinction between simple and complex cells of the visual cortex are examined. The classification of visual cells on the basis of their spike response as simple or complex, first proposed by Hubel and Wiesel in 1962, is commonly accepted by neuroscientists (Skottun et al, 1991) as one of the basic features of primary visual cortex.  The synaptic organization of simple and complex cells is presumed categorically distinct and as such is crucial to the so-called hierarchical models of cortical organization.  Nearly all of the experimental and theoretical studies of visual cortex address these two populations separately.

        Recently, an alternative explanation was offered (Mechler and Ringach 2002) for the simple/complex dichotomy.  In this "threshold model", the dichotomy is a nonlinear emergent phenomenon.  Here I present intracellularly recorded responses that confirm the threshold model.  We demonstrate that although spiking responses form a bimodal distribution, the membrane potential responses form a unimodel distribution, and that the difference between them is accounted for by the nonlinearity of the spike threshold.  Our work presents evidence that it is a mechanistic continuum rather than a dichotomy that underlies the distinction between simple and complex cell responses.  This talk is based on work done in collaboration with members of David Ferster's lab (Priebe et al 2003).