The intensity of brain activity determines the need for sleep

According to a new UCL study on zebrafish, the intensity of cerebral activity during the day, despite the time spent staying awake, seems to increase our need for sleep.

The research, published in neuron, found a gene that responds to brain activity to coordinate the need for sleep. This helps to better understand how sleep is regulated in the brain.

"There are two systems that regulate sleep: the circadian system and the homeostatic system.We understand quite well the circadian system – our integrated 24-hour clock that tracks our biological rhythms, including sleep cycles, and we know where that rhythm is. found in the brain, "says Dr. Jason Rihel (Biology of Development and Cells at UCL).

"But the homeostatic system, which causes a feeling of growing tiredness after a very long day or a sleepless night, is not well understood.What we have found is that it seems like not be motivated by how long you wake up, but how intense your brain activity has been since your last sleep. "

To understand the brain processes that regulate homeostatic regulation of sleep, regardless of the time of day, the research team studied zebrafish larvae.

Zebrafish is commonly used in biomedical research, partly because of its nearly transparent bodies that facilitate imaging, in addition to similarities with humans, such as sleeping every night.

The researchers facilitated the increase in zebrafish brain activity with the help of various stimulants, including caffeine.

Zebrafish whose increased brain activity was induced by drugs slept longer after the disappearance of the drug, thus confirming that increased brain activity was contributing to increased need for sleep.

Researchers have found that a specific zone of the zebrafish brain is at the heart of the effect on sleep pressure: an area of ​​the brain comparable to that of the human brain located in the hypothalamus, known to be active during sleep . In the cerebral zone of zebrafish, a specific cerebral signaling molecule called galanin was particularly active during restorative sleep, but did not play such an important role during nighttime sleep.

To confirm that the results induced by the drug were relevant for lack of sleep, the researchers conducted a test by keeping the young zebrafish awake all night on a treadmill where the stripes were moving, mimicking the white water, gives fish the impression that they need to keep swimming. Zebrafish kept at rest slept more the next day and their brains showed an increase in galanin activity during restorative sleep.

The results suggest that galanin neurons may track total brain activity, but additional research is needed to clarify how they detect what is happening throughout the brain.

Researchers say their discovery that excessive brain activity can increase the need for sleep may explain why people often feel exhausted after a crisis.

"Our results could also explain how some animals can avoid sleeping under certain conditions, such as starvation or the mating season – it is possible that their brains can minimize brain activity to limit sleep requirements." said the first author of the study, Dr. Sabine Reichert (Cell Biology and Developmental).

The researchers say that by discovering a gene playing a central role in the homeostatic regulation of sleep, their findings could help understand sleep disorders and sleep disorders, such as Alzheimer's disease.

"We may have identified a good drug for sleep disorders because it may be possible to develop therapies acting on galanin," added Dr. Reichert.