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Neurosci Biobehav Rev. 2017 Jul;78:24-33. doi: 10.1016/j.neubiorev.2017.04.016. Epub 2017 Apr 23.

Chromatic clocks: Color opponency in non-image-forming visual function.

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Stanford University, Department of Psychiatry & Behavioral Sciences, Stanford, CA, USA; VA Palo Alto Health Care System, Mental Illness Research Education and Clinical Center, Palo Alto, CA, USA. Electronic address:
University of Manchester, Faculty of Life Sciences, Manchester, United Kingdom.


During dusk and dawn, the ambient illumination undergoes drastic changes in irradiance (or intensity) and spectrum (or color). While the former is a well-studied factor in synchronizing behavior and physiology to the earth's 24-h rotation, color sensitivity in the regulation of circadian rhythms has not been systematically studied. Drawing on the concept of color opponency, a well-known property of image-forming vision in many vertebrates (including humans), we consider how the spectral shifts during twilight are encoded by a color-opponent sensory system for non-image-forming (NIF) visual functions, including phase shifting and melatonin suppression. We review electrophysiological evidence for color sensitivity in the pineal/parietal organs of fish, amphibians and reptiles, color coding in neurons in the circadian pacemaker in mice as well as sporadic evidence for color sensitivity in NIF visual functions in birds and mammals. Together, these studies suggest that color opponency may be an important modulator of light-driven physiological and behavioral responses.


Circadian rhythms; Color opponency; Color vision; Non-image-forming vision; Retina; Sleep-wake cycles

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