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This Article Full Text Full Text (PDF) All Versions of this Article: 579/1/29    most recent jphysiol.2006.122283v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Victor, J. D. Articles by Martin, P. R. Search for Related Content PubMed PubMed Citation Articles by Victor, J. D. Articles by Martin, P. R. Related Collections Neuroscience

¹ Department of Neurology and Neuroscience, Weill Medical College of Cornell University, New York, NY 10021, USA
² National Vision Research Institute of Australia, Cnr Keppel and Cardigan Streets, Carlton 3053, Australia
³ Department Optometry & Vision Sciences, University of Melbourne, Parkville, VIC 3052, Australia

This study concerns the properties of neurons carrying signals for colour vision in primates. We investigated the variability of responses of individual parvocellular lateral geniculate neurons of dichromatic and trichromatic marmosets to drifting sinusoidal luminance and chromatic gratings. Response variability was quantified by the cycle-to-cycle variation in Fourier components of the response. Averaged across the population, the variability at low contrasts was greater than predicted by a Poisson process, and at high contrasts the responses were approximately 40% more variable than responses at low contrasts. The contrast-dependent increase in variability was nevertheless below that expected from the increase in firing rate. Variability falls below the Poisson prediction at high contrast, and intrinsic variability of the spike train decreases as contrast increases. Thus, while deeply modulated responses in parvocellular cells have a larger absolute variability than weakly modulated ones, they have a more favourable signal: noise ratio than predicted by a Poisson process. Similar results were obtained from a small sample of magnocellular and koniocellular (‘blue-on’) neurons. For parvocellular neurons with pronounced colour opponency, chromatic responses were, on average, less variable (10–15%, p < 0.01) than luminance responses of equal magnitude. Conversely, non-opponent parvocellular neurons showed the opposite tendency. This is consistent with a supra-additive noise source prior to combination of cone signals. In summary, though variability of parvocellular neurons is largely independent of the way in which they combine cone signals, the noise characteristics of retinal circuitry may augment specialization of parvocellular neurons to signal luminance or chromatic contrast.

(Received 4 October 2006; accepted after revision 17 November 2006; first published online 23 November 2006)
Corresponding author P. R Martin: National Vision Research Institute of Australia, Cnr Keppel and Cardigan Streets, Carlton, VIC 3053, Australia. Email: prmartin{at}unimelb.edu.au