Cones are required for normal temporal responses to light of phase shifts and clock gene expression

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Summary

Middle-wavelength cones play a critical role in the initial phasic response to light that drives circadian phase shifts and SCN clock gene induction, particularly for mid-to-long wavelengths (480–530 nm). For lighting design, this implies that cone-mediated responses at light onset are important for robust circadian entrainment, and that short-wavelength (360 nm) stimulation alone is insufficient to fully substitute for cone input.

Key Findings

Mice lacking MW-cones showed reduced behavioral phase shifts in response to short-duration light stimulations at 480 nm and 530 nm, but not at 360 nm.
Induction of clock genes mPer1 and mPer2 mRNA in the SCN was attenuated in MW-cone-deficient mice for mid-to-long wavelength light exposures.
Modeling of photoresponses indicated an overall reduction in circadian sensitivity in MW-cone-lacking mice, with the deficit increasing at longer wavelengths.
Results support a model where cones provide a strong initial phasic input at light onset and may prime ipRGC responses to sub-threshold light exposures.