Ongoing spontaneous activity in the cerebral cortex exhibits complex spatiotemporal patterns in the absence of sensory stimuli. To elucidate the nature of this ongoing activity, we present a theoretical treatment of two contrasting scenarios of cortical dynamics: (1) fluctuations about a single background state and (2) wandering among multiple "attractor" states, which encode a single or several stimulus features. Studying simplified network rate models of the primary visual cortex (V1), we show that the single state scenario is characterized by fast and high-dimensional Gaussian-like fluctuations, whereas in the multiple state scenario the fluctuations are slow, low dimensional, and highly non-Gaussian. Studying a more realistic model that incorporates correlations in the feed-forward input, spatially restricted cortical interactions, and an experimentally derived layout of pinwheels, we show that recent optical-imaging data of ongoing activity in V1 are consistent with the presence of either a single background state or multiple attractor states encoding many features.
Bibliographical noteFunding Information:
This research was partially supported by a grant from the US-Israel BSF. J.A.G. and U.R. were supported by the Yeshaya Horowitz Association. We thank T. Kenet, A. Arieli, M. Tsodyks, and A. Grinvald for providing us with their optical map data (Figure 6A) . We are also grateful to them for many valuable discussions and clarifications concerning their experimental results. We thank Y. Loewenstein for his critical reading of an earlier version of the manuscript.