This is talk 19 (of 31) at the Conference on Brain Network Dynamics held at the University of California at Berkeley on January 26-27, 2007. Speaker is Friedrich T. Sommer, from the Redwood Center for Theoretical Neuroscience, University of California Helen Wills Neuroscience Institute, Berkeley, CA. http://redwood.berkeley.edu/wiki/Fritz_Sommer

Abstract:
Visually evoked changes in retinal firing rate convey information downstream to the thalamus and to cortex. It is widely held that retinal spike trains code information about the visual stimulus solely by a process that depends on how reproducibly firing rates lock to stimulus onset, that is, by stimulus-locked coding. Yet retinal firing patterns are not only influenced by external stimuli but also by dynamics of intrinsic neuronal networks. In fact, work in other systems suggests that information can be encoded by stimulus-induced changes in ongoing oscillatory activity. Thus it is natural to ask if the early visual system processes sensory information not only by means of stimulus-locked coding but also by a mechanism that compares spike timing to intrinsic activity. To address this question we used whole-cell recording in vivo to record retinal EPSPs and the spikes they evoke from relay cells in the lateral geniculate nucleus of the thalamus in response to naturalistic stimuli. Using information theory to interpret the results, we found that visual information can indeed be transmitted by two separate channels. The first channel transmits stimulus locked information about patterns within the receptive field and is limited to relaying visual signals slower than 30 Hz. The second, novel, channel uses spike timing relative to intrinsic retinal oscillations at fine temporal scales, corresponding to the gamma band (50-70 Hz). Remarkably, the amount of information in the second channel could match or even exceed that conveyed by the first, a result that we were able to reproduce in a simple model of a relay cell. Because retinal oscillations involve large-scale networks, the novel channel could convey distributed, contextual aspects of the stimulus that complement stimulus-locked information about local features.

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