HUMAN CIRCADIAN RHYTHM MODULATION AND ITS EFFECTS ON PHYSIOLOGICAL AND BEHAVIOURAL RESPONSES

Abstract

Intrinsically photosensitive retinal ganglion cells containing the photopigment melanopsin play an important role in non-visual photoreceptive functions including photoentrainment of endogenous circadian rhythms and the pupillary light reflex (PLR). By using light exposures at wavelengths designed to target cone photoreceptors instead of melanopsin, we observed that intermittent long-wavelength light is capable of evoking a more sustained PLR than constant illumination. By comparison, we found no significant differences in circadian responses for exposure to continuous versus intermittent long-wavelength light. Nevertheless, a subset of participants exposed to long-wavelength light showed circadian phase delay shifts of a magnitude comparable to bright white light exposure, suggesting that cone photoreceptors are capable of driving large circadian responses. Concurrently, our experimental protocol allowed us to study sleepiness and attention under both normal and shift work-like conditions. We show that heart rate variability measures can be useful adjuncts to ocular measures in predicting lapses in sustained attention.