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The Journal of Neuroscience, October 25, 2006, 26(43):11148-11161; doi:10.1523/JNEUROSCI.3237-06.2006

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Behavioral/Systems/Cognitive
Specificity of M and L Cone Inputs to Receptive Fields in the Parvocellular Pathway: Random Wiring with Functional Bias

Péter Buzás,^1,2 Esther M. Blessing,^1,2 Brett A. Szmajda,^1,2 and Paul R. Martin^1,2

¹National Vision Research Institute of Australia, Carlton, Victoria 3053, Australia, and ²Department of Optometry and Vision Sciences, The University of Melbourne, Parkville, Victoria 3052, Australia

Correspondence should be addressed to Paul R. Martin, National Vision Research Institute of Australia, Corner of Keppel and Cardigan Streets, Carlton, Victoria 3053, Australia. Email: prmartin{at}unimelb.edu.au

Many of the parvocellular pathway (PC) cells in primates show red–green spectral selectivity (cone opponency), but PC ganglion cells in the retina show no anatomical signs of cone selectivity. Here we asked whether responses of PC cells are compatible with "random wiring" of cone inputs. We measured long-wavelength-sensitive (L) and medium-wavelength-sensitive (M) cone inputs to PC receptive fields in the dorsal lateral geniculate of marmosets, using discrete stimuli (apertures and annuli) to achieve functional segregation of center and surround. Receptive fields between the fovea and 30° eccentricity were measured.

We show that, in opponent PC cells, the center is dominated by one (L or M) cone type, with normally <20% contribution from the other cone type (high "cone purity"), whereas non-opponent cells have mixed L and M cone inputs to the receptive field center. Furthermore, opponent response strength depends on the overall segregation of L and M cone inputs to center and surround rather than exclusive input from one cone type to either region. These data are consistent with random wiring. The majority of PC cells in both foveal (<8°) and peripheral retina nevertheless show opponent responses. This arises because cone purity in the receptive field surround is at least as high as in the center, and the surround in nearly all opponent PC cells is dominated by the opposite cone type to that which dominates the center. These functional biases increase the proportion of opponent PC cells, but their anatomical basis is unclear.

Key words: color vision; primate; parvocellular; receptive fields; lateral geniculate nucleus; vision

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Received April 4, 2006; revised Sept. 11, 2006; accepted Sept. 21, 2006.

Correspondence should be addressed to Paul R. Martin, National Vision Research Institute of Australia, Corner of Keppel and Cardigan Streets, Carlton, Victoria 3053, Australia. Email: prmartin{at}unimelb.edu.au

This article has been cited by other articles:

				J. D. Victor, E. M. Blessing, J. D. Forte, P. Buzas, and P. R. Martin Response variability of marmoset parvocellular neurons J. Physiol., February 15, 2007; 579(1): 29 - 51. [Abstract] [Full Text] [PDF]

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