According to experts, sleep is practically universal among animals. The exact purpose of sleep remains a mystery, and there are many theories about why it is so essential to our health.
Biologists at Arizona State University found in past studies that some animals do not seem to sleep as deeply as others, such as dolphins and bullfrogs. They also discovered that bees do not need as much rebound sleep after expending their energy.
The harmful effects of sleep deprivation in humans have been well documented, including an increased risk of high blood pressure, heart disease, diabetes, and obesity. Poor sleeping habits have also been linked to depression.
The most common theory about the function of sleep is that it helps to consolidate memories, and is critical to the learning process.
Researchers have previously mapped the brain circuits that induce sleep at the beginning of the night as well as those that suppress sleep at the end of the night. Despite this insight, it has still remained unclear how the brain stays awake and alert during the day.
In the current study, Sheetal Potdar and Sheeba Vasu have identified a subset of dopaminergic neurons which are slowed down during the day by the light-responsive neuropeptide Pigment Dispersing Factor (PDF) and its receptor (PDFR).
The team found that inhibiting the expression of the PDFR-encoding gene in this subset increased sleep during the day. When the expression of the gene was increased, daytime sleep was reduced.
The findings suggest that high daytime levels of PDF promote wakefulness by blocking the activity of sleep-promoting dopaminergic neurons.
The study may help researchers to better understand sleep and wake cycles in humans, which are very similar to those of other mammals.
The research is published in the journal eNeuro.