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G. D. Field, J. L. Gauthier, M. Greschner, A. Sher, L. Jepson, A. M. Litke, E. J. Chichilnisky; Retinal Ganglion Cell Nonlinear Subunit Structure at Single-Cone Resolution. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5176.
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© ARVO (1962-2015); The Authors (2016-present)
An important aspect of retinal processing is the existence of nonlinear subunits in the receptive fields of retinal ganglion cells (RGCs). These subunits produce nonlinear (frequency-doubling) responses in Y-type cells in cat and primate retina, and have been implicated in higher-level computations such as objection motion sensitivity in amphibian and rabbit retina. However, little is known about the receptive fields of subunits, specifically how they are assembled from the inputs of individual cones.
Recordings were performed in vitro from RGCs in peripheral primate retina using a 512-electrode recording system. ON and OFF midget and parasol RGCs, the numerically dominant RGC types in primate retina, were uniquely identified based on their light response properties, density, and mosaic organization of receptive fields. Visual stimulation with fine-grained white noise stimuli, and linear reverse correlation analysis, were used to measure the receptive fields of midget and parasol cells at the resolution of single cones.
Nonlinear interactions between cones were revealed by spike-triggered covariance analysis. The distribution of stimuli that immediatedly preceded spikes in a given RGC was accumulated, and the eigenvectors of the covariance matrix were computed. Eigenvectors often displayed clear spatial structure: spatially contiguous collections of cones suggestive of receptive field subunits. These were absent in the eigenvectors obtained with randomly shifted spike times, and were not reproduced by optical blur or simple models which include a static nonlinearity before or after summation of cone inputs. OFF cells exhibited stronger subunit structure than ON cells, consistent with differences in the degree of nonlinearity.
The subunit structure of RGC receptive fields may be identified and visualized at high resolution with a combination of single-cone resolution receptive field measurements and spike-triggered covariance analysis.
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