Access to self-selected light (SSL) breaks the ancient relationship between light and time of day and can disrupt sleep and circadian rhythms in humans. Such disruptions have been explained in terms of established features of circadian photosensitivity and positive associations between arousal and light. We address the potential of such intrinsic relationships to recapitulate the disruptive effects of SSL in a day-active rodent (Rhabdomys pumilio [R. pumilio]) that lacks the additional human drivers to consume light for work, care, and leisure. R. pumilio learns to SSL spontaneously and expresses a circadian rhythm in light intensity preference (choosing darkness and brightest available light for inactive and active phases, respectively), which feeds back to modify circadian period (τ) and extend active phase (α). Under imposed light:dark (LD) cycles, SSL can lead to increased dark phase activity and disrupted entrainment when SSL irradiance is ≥ imposed light. SSL does not exacerbate aberrant phase angles of entrainment in simulated social jet lag but can substantially delay re-entrainment to shifts in the external LD cycle. Our findings establish bright light as an innate preference in R. pumilio and are consistent with intrinsic relationships between light, arousal, and the clock being an origin for the disruptive effects of SSL.
Circadian Biology