Why does darkness make us sleepy
Scientists found a protein that could explain why darkness makes us sleep while light has the power of waking us up.
Scientists already know the impact that light has on our circadian rhythms but now, a new find could also explain the effect of light on sleep answering questions such as why does darkness make us sleep and why light has the power of waking us up.
We’ve all experienced being woken up when somebody switched on the light in our bedroom and, according to Caltech researchers in the laboratory of Professor of Biology David Prober, this could be due to a specific protein in the brain that responds to light and darkness and sets the correct balance between sleep and wakefulness.
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“Researchers had previously identified the photoreceptors in the eye that are required for the direct effect of light on wakefulness and sleep,” says Prober. “But we wanted to know how the brain uses this visual information to affect sleep.”
To find the answer how light impacts sleep, scientists used zebrafish which allow for a non-invasive imaging of their neurons. To investigate how their sleep responds to light, Wendy Chen, a former graduate student in Prober’s lab, led studies examining a particular protein in the zebrafish brain called prokineticin 2.
Scientists observed that genetically engineered zebrafish, with an abundance of the new protein, were more likely to fall asleep during the day and to wake up at night. Surprisingly, the effects did not depend on the engineered fish’s normal circadian sleep/wake cycle but rather depended only on whether the lights were on or off in their environment.
This suggests that an excess of Prok2 suppresses both the usual awakening effect of light and the sedating effect of darkness.
“Though diurnal animals such as zebrafish spend most of their time asleep at night and awake during the day, they also take naps during the day and occasionally wake up at night, similar to many humans,” Prober says. “Our study’s results suggest that levels of Prok2 play a critical role in setting the correct balance between sleep and wakefulness during both the day and the night.”
Relying on their findings, scientists say that further work is needed to fully explain how light and dark directly affect sleeping and waking, and to determine whether Prok2 has a similar function in humans.
The study, published in the journal Neuron, could help to the development of new sleep and wake promoting medication.
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