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The Journal of Neuroscience, January 30, 2008, 28(5):1131-1139; doi:10.1523/JNEUROSCI.4682-07.2008

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Behavioral/Systems/Cognitive
Habituation Reveals Fundamental Chromatic Mechanisms in Striate Cortex of Macaque

Chris Tailby,¹ Samuel G. Solomon,² Neel T. Dhruv,¹ and Peter Lennie^1,3

¹Center for Neural Science, New York University, New York, New York 10003, ²Bosch Institute and School of Medical Sciences, The University of Sydney, Sydney, New South Wales 2006, Australia, and ³Center for Visual Science and the Department of Brain and Cognitive Sciences, University of Rochester, Rochester, New York 14627

Correspondence should be addressed to Chris Tailby, National Vision Research Institute of Australia, Department of Optometry and Vision Sciences, University of Melbourne, Corner Keppel and Cardigan Streets, Carlton, Victoria 3053, Australia. Email: ctaiby{at}unimelb.edu.au

Prolonged viewing of a chromatically modulated stimulus usually leads to changes in its appearance, and that of similar stimuli. These aftereffects of habituation have been thought to reflect the activity of two populations of neurons in visual cortex that have particular importance in color vision, one sensitive to red–green modulation, the other to blue–yellow, but they have not been identified. We show here, in recordings from macaque primary visual cortex (V1), that prolonged exposure to chromatic modulation reveals two fundamental mechanisms with distinctive chromatic signatures that match those of the mechanisms identified by perceptual observations. In nearly all neurons, these mechanisms contribute to both excitation and to regulatory gain controls, and as a result their habituation can have paradoxical effects on response. The mechanisms must be located near the input layers of V1, before their distinct chromatic signatures diffuse. Our observations suggest that the fundamental mechanisms do not give rise to two distinct L–M and S chromatic pathways. Rather, the mechanisms are better understood as stages in the elaboration of chromatic tuning, expressed in varying proportions in all cells in V1 (and beyond), and made accessible to physiological and perceptual investigation only through habituation.

Key words: vision; color; macaque; habituation; contrast adaptation; normalization; striate cortex; cardinal directions

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Received Aug. 21, 2007; revised Dec. 11, 2007; accepted Dec. 13, 2007.

Correspondence should be addressed to Chris Tailby, National Vision Research Institute of Australia, Department of Optometry and Vision Sciences, University of Melbourne, Corner Keppel and Cardigan Streets, Carlton, Victoria 3053, Australia. Email: ctaiby{at}unimelb.edu.au

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