Circadian rhythms are linked to the external light-dark cycle through inputs from photoreceptors that signal into networks that regulate neural and physiological function. One of the key photoreceptors is CRYPTOCHROME, which is sensitive to blue-light wavelengths. Fogle et al. now find that CRYPTOCHROME has an unexpectedly direct effect on circadian physiology in fruit flies. A small group of neurons that are part of the circadian circuit and that are usually more active in the morning express CRYPTOCHROME. These neurons normally receive plenty of input from the circadian circuit that perceives cycles and drives responses. However, when those inputs are blocked, it seems that these neurons are able to respond directly to blue light.
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