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G. D. Field, J. L. Gauthier, M. Greschner, J. Shlens, A. Sher, A. M. Litke, E. J. Chichilnisky; Light Adaptation Changes the Size of Receptive Fields in Seven Distinct Primate Retinal Ganglion Cell Types. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3856.
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© ARVO (1962-2015); The Authors (2016-present)
We sought to determine how different retinal ganglion cell (RGC) types in primate retina adapt to changes in the mean light level. Our aims were to: (1) identify the RGC types that receive rod input; (2) measure light-level dependent changes in spatial and temporal receptive field properties; and (3) test possible mechanisms that mediate changes in receptive fields.
A large-scale multielectrode recording system was used to make extracellular recordings from hundreds of RGCs in ~1 x 2 mm (~4 x 8 deg) pieces of peripheral macaque retina. Reverse correlation with a white noise stimulus was used to estimate the spatial, temporal and chromatic properties of receptive fields. These properties were used to functionally classify RGCs in each recording. Anatomical measurements taken from the literature were used to establish correspondences between observed functional cell classes and known morphological cell types.
Recordings were obtained from ON and OFF parasol and midget cells, small bistratified cells, and two additional RGC types of unknown morphological type,at scotopic, mesopic, and photopic light levels. Receptive fields of all seven cell types were measurable at a scotopic light level (~0.3 Rh*/rod/s) expected to reveal pure rod input to RGCs via the A2-amacrine cell pathway. At higher light levels, all RGC types showed substantial decreases in receptive field size. However, midget cells showed larger fractional decreases than parasol cells, and OFF cells showed larger fractional decreases than ON cells. Additionally, the receptive field surround of midget and parasol cells was nearly absent at low scotopic light levels, but clear at higher light levels. We tested whether the change in receptive field size could be explained by the absence of a surround at scotopic light levels. The observed change in receptive field size was 4-8 fold greater what would be expected from the absence of the surround.
All primate RGC types identified in this study exhibited clear rod inputs at low scotopic light levels, and substantial decreases in receptive field size at higher light levels. These results, and the light levels probed in this study, are suggestive that A2-amacrine cells make promiscuous contacts with many (perhaps all) cone bipolar cell types in peripheral primate retina. The change in receptive field size as a function of light level is more likely mediated by mechanisms other than changes in the strength of the inhibitory surround.
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