The impact of self-selected light on activity rhythms in the diurnal striped mouse

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 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 learn to self-select light spontaneously and express 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 jetlag 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 disruptive effects of SSL.