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Cheng Chi Chu, Chou Po Hung; Clustering of macaque V1 neurons by luminosity function. Journal of Vision 2009;9(8):315. doi: 10.1167/9.8.315.
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Neurons in primary visual cortex (V1) respond to both luminance and color and are integral to the transformation of color representation from retinal cone axes to perceptual hues. To isolate the coding and circuitry underlying this transformation, we employed the silent substitution method to minimize luminance-related responses. The silent substitution method depends on the choice of luminosity function, typically defined as sensitivity to a ratio of L and M cone subtypes. As the field has not agreed upon a unique luminosity function to study color representation in macaque V1, we began by testing whether the choice of luminosity function, human (1.5L + M) or macaque (1L + 1M, Dobkins et al. 2000), affects the quality of isolation of the color circuitry.
We used intrinsic signal optical imaging to identify blob and interblob structures and measured single-unit responses via targeted multi-electrode arrays in anaesthetized macaque V1. Stimuli consisted of 4 Hz chromatically-modulated drifting gratings presented monocularly.
Our initial results indicate that a heterogeny of luminosity functions are represented by V1 neurons, with a tendency for neurons with similar luminosity functions to cluster together in cortex. This finding is consistent with reports of local clustering of L and M cone subtypes in the human and macaque retina, suggesting that this spatial non-uniformity of spectral sensitivity persists in the color representation through to V1.
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