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Tyler Godat, Juliette E. McGregor, Keith Parkins, William H. Merigan, David R. Williams; In vivo classification of macaque foveal ganglion cells through optical recording of responses to chromatic and luminance flicker. Journal of Vision 2019;19(15):19. doi: https://doi.org/10.1167/19.15.19.
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© ARVO (1962-2015); The Authors (2016-present)
Despite the significance of the fovea for primate vision, its physiology is much less understood than the peripheral retina. We functionally classified foveal cells in in the ganglion cell layer (GCL) of a female macaque that express a genetically encoded calcium indicator (GCaMP6s), allowing optical recording of the responses to chromatic and luminance flicker. Adaptive optics scanning light ophthalmoscopy (AOSLO) was used to image GCaMP6 fluorescence (488 nm excitation, 500–540 nm emission) from a ring of displaced GCL cells driven by cones in the central fovea. We recorded responses to sinusoidal flicker (0.2 Hz, LED 420 nm, 530 nm, 660 nm) modulated in one of three orthogonal directions in color space: white luminance modulation, a modulation calculated to maximize the counterphase excitation of M and L cones while silencing S cones, and a modulation to drive S cones while silencing M and L cones. We calculated the amplitude and phase from the fluorescence responses of 205 cells.
Response to luminance flicker demonstrated ON and OFF dominant types of cells, while response to the chromatic stimuli reveal cone inputs. 62% of cells were responsive to the M-L cone flicker, and 14% were responsive to the S cone flicker. 3% of cells were responsive to luminance flicker, but unresponsive to either chromatic stimulus. 24% of cells were unresponsive to all three stimuli. By expanding the stimulus space further, this method has the potential to provide a complete characterization of the retinal ganglion cell classes in the primate fovea.
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