The long-term goal of this project is to elucidate the temporal and spatial filtering of signals in the vertebrate retina and to understand how they contribute to the efficient performance of key visual tasks. To do this we must also learn how to decode, in real time, the information carried in the spike train of the retinal ganglion cell. We will make use of recent theoretical developments which quantify the performance of the system relative to the optimum and which allow us to determine the information content of the spike train. Specifically, in the salamander, we propose to explore the effects of light adaptation on a filter that we earlier showed to be located between the rod and the bipolar cell, and whose properties are matched to the signal and noise properties of the rods. Matched filtering is an essential first step towards the efficient performance of all visual tasks under conditions of low signal-to-noise. We shall repeat this analysis on the cone pathway of the retina. We shall also learn how to reconstruct the visual stimulus from the ganglion cell's spike train and in so doing, characterize temporal filtering at more proximal levels in the retina. The effects of light adaptation on this filtering will also be determined. We shall also determine how the spike generating mechanism helps to restore information, carried in the slow retinal signals, to the time scale of the stimulus. Initially, we shall address the question of how the retina contributes to the optimal encoding of the time-varying intensity of the stimulus. These experiments will involve intracellular and extracellular recording techniques and suction pipette recordings from photoreceptors. In parallel experiments we shall study the pharmacology of amacrine and ganglion cells with a view to establishing the possible contribution of the kinetics of transmitter-activated conductances to temporal filtering. The proposed studies will contribute to the localization of neural mechanisms essential to the performance of key visual tasks and thus will aid in the diagnosis and treatment of specific visual disorders.
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