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Christopher L. Passaglia, Gilberto D. Grana; Effect Of Contrast On The Linearity Of Center And Surround Responses. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4570.
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© ARVO (1962-2015); The Authors (2016-present)
Though rats are a popular model for vision studies, the functional properties of their retinal ganglion cells (RGC) remain poorly understood. The aim of this study was to characterize the linearity and response dynamics of the receptive field center and surround mechanisms of these cells. In so doing, we sought to compare two common measures of linear dynamics: the temporal frequency response and the spike-triggered average.
Adult Brown-Norway rats were anesthetized and ganglion cell spike trains were recorded with optic tract electrodes. The temporal frequency response of recorded cells was measured using sinewave-modulated gratings of threshold contrast that preferentially stimulated the receptive field center or surround. The spike-triggered average response was measured using binary white-noise modulated spots and annuli of varying contrast. The two measures were then directly compared by calculating the Fourier transform of the spike-triggered averages.
The temporal frequency responses to a sinewave grating optmized for center stimulation had a similar high-frequency cutoff as the noise-modulated spot responses for ON and OFF cells, but the latter of the responses showed greater low-frequency attenuation. The power spectrum of the spike-triggered average also depended strongly upon the contrast of the white-noise stimulus. For both types of stimuli, surround responses exhibited considerable power at frequencies above the cutoff of center responses. This was concomitantly reflected in more transient response profiles to full field stimuli.
The linear filter estimated by white noise analysis differs from that given by direct measurement, implying that the spike triggered average misestimates the retinal filter somewhat. This may be due to adaptational effects induced by the constant broadband power of the stimulus. The response dynamics of rat ganglion cells are strongly influenced by stimulus size and contrast, with both their receptive field center and surround responses being affected. The surround dynamics are faster than the center and more strongly excited by large flickering stimuli.
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