Light is a defining environment factor that synchronizes the circadian clock with a period close 24 hours. The master circadian clock is located in suprachiasmatic nucleus (SCN),it is endogenously driven by the oscillations of clock genes. given that the SCN projects to brain functional structures, it confine behavioral and physiological activities to specific times of the day-night cycle. In overall, During daytime, light has a positive effect as it favors wakefulness in diurnal species. A night or prior to bedtime, light has a detrimental impact as it inhibits sleep and sleepiness. Giving the effect of light on circadian phase，sleep and wakefulness,physiological performance.what do these effects comes from? They come from and happened via a specific photoreceptor ipRGCs in the retina interface, located in the inner retina, convey light information mainly for non-visual functions, such as sleep–wake and circadian rhythm regulation. The ipRGCs integrate and transmit photic information via the retino-hypothalamic tract (RHT) directly to the suprachiasmatic nuclei (SCN) , thereby entraining the circadian timing system to the daily 24-h light/dark cycle.
Besides the SCN, ipRGCs also project to a diverse set of nuclei in the VLPO, locus coeruleus, the medial amygdala, the lateral habenula and the subparaventricular zone. As such, light conveyed by ipRGCs has direct effects on a variety of non visual functions that not through the indirect pathway SCN(e.g., circadian rhythms, pupil light reflex, sleep–wake cycle.
The interesting questions we want to investigate are aimed at understanding the mechanisms involved in the effects of light on sleep, wakefulness and health, in a diurnal animal model and in humans. What are the photobiological mechanisms involved? How does light exposure at night impact sleep? What are the brain structures and neurotransmitters activated/inhibited by light?