It happens. You wake during the night without any particular reason. You reach for your phone to either a) check the time to see how much potential sleep time remains or b) to kill time until you doze off again. There’s been discussion that this burst of bright light during the night can interrupt your overall sleep quality for the night and even disrupt your ongoing circadian rhythm. The current thought is that light is passed from the environment to intrinsically photosensitive retinal ganglion cells (ipRCGs) in the suprachiasmatic nucleus located in the hypothalamus. It’s there where the circadian rhythms are controlled.
A recent study has looked into confirming this in a set up that is all too familiar to everyone, whether if middle of the night phone usage does have lasting effects on your sleep. The study, conducted by Schmidt et al., used a genetically modified mouse model that only had ipRGCs projecting to the SCN and no other regions. Mice are nocturnal and as such, they fall asleep when exposed to light. The mice in this experiment stayed awake during the short pulses of light (their body temperature also remained the same, which is a correlate to sleep). The mice maintained their normal sleep/wake cycle (and body temperature) throughout the experiment.
This study shows that there are multiple pathways that transmit light sensations into the brain for processing, not just the route to the SCN. Furthermore, it confirms that these short bursts of light, aka a phone screen, during the middle of the night won’t have an overall effect on one’s circadian rhythm though it may cause an unrestful sleep the following day. Using this knowledge, more work can potentially be done in using light to aid those to increase alertness in those who require it, eg: shift workers, while lowering the harmful effects to the circadian rhythm.
