People often look at their smartphones before going to sleep or after waking in the middle of the night. What are the effects of this on the human body and does this activity impact on sleep patterns?
To explore these topics, researchers at Northwestern University have confirmed that an acute burst of light can make it more difficult for a person to fall back to sleep. However, the light does not interfere with the body’s overall circadian rhythms and the next night of sleep is not disrupted.
The scientists examined the effects of short pulses of light on the brain in relation to sleep. This led to the discovery that different areas of the brain are responsible for processing short pulses of light, compared with long-term exposure to light.
This finding calls into question the conventional idea that all light information is processed by the same brain region – the suprachiasmatic nucleus (SCN). The SCN region functions to synchronize an animal’s sleep/wake cycles.
Commenting on the outcome, lead researcher Dr. Tiffany Schmidt notes: “Prior to the widespread use of electricity, our exposure to light and darkness occurred in a very predictable pattern. But light has become very cheap. We all have smartphones, and their screens are very bright.”
This means, she continues: “We’re all getting exposed to light at the wrong times of day. It’s becoming more important to understand how these different types of light information are relayed to the brain.”
The research found that once light enters the eye, specialized neurons (termed intrinsically photosensitive retinal ganglion cells) carry the light information to the brain. This effect was demonstrated using a genetically modified mouse model.
By exposing nocturnal mice to light through a succession of experiments, it was found that the mice maintained a normal sleep/wake cycle and normal rhythms in their body temperature, indicating their circadian rhythms remained intact.
The research has genetically identified two circuits that relay light to affect sleep. This finding may assist researchers in optimizing light to achieve alertness while simultaneously mitigating problematic shifts with a person’s circadian rhythms (something essential to understand for night shift workers, for example). Further work will be undertaken to map the pathways involved.
The research paper, which is in the pre-print stage for the journal eLife, is titled “Distinct ipRGC subpopulations mediate light’s acute and circadian effects on body temperature and sleep.”
