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M. Kamermans, M.T. Van Leeuwen, R. Numan, T. Sjoerdsma, I. Fahrenfort; Surround Stimulation Leads to Potentiation of Ganglion Cells Center Responses . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3107.
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Psychophysical experiments show that the sensitivity for a flickering stimulus dependends strongly on the intensity of the surround illumination. This is not inline with the concept of an inhibitory surround. In this paper we show that these two phenomena are not mutual exclusive and we will present evidence that the enhancement of flicker sensitivity has a retinal origin. At the photoreceptor – horizontal cell synapse a gain control mechanism is functioning with the properties required for such a task.
Patch–clamp, intracellular and extracellular recordings were made from respectively cones, horizontal cells and ganglion cells in the isolated goldfish retina. The retina was stimulated with spots of sine wave modulated light with various contrasts and intensities. The influence of sustained surround stimulation on the responsiveness of the neurons was studied. A computational model based on the known physiological properties of the cone – horizontal cell interactions was developed.
We will show that steady surround stimulation of the inhibitory surround of the ganglion cells leads to a potentiation of the center responses of ganglion cells to sinusoidal modulated light in the center. Similar effects could be found on HC level whereas they were absent in the cones. The mechanism for the potentiation of the center response is the feedback mechanism from horizontal cells to cones. The model was tested with similar stimulus protocols. The model can adequately reproduce the experimental results.
Although surround stimulation is generally known to inhibit the center response, the present data show that sustained surround stimulation can also lead to an enhanced response to a sine–wave modulated light in the center. Surround inhibition is subtractive as well as divisive. This influence of the surround can adequately be accounted for by the feedback mechanism from horizontal cells to cones. This mechanism might be underlying the psychophysical experiments that show that the sensitivity for a flickering stimulus increases with steady surround illumination.
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