Scientists find in the brain a "switch" that allows us to sleep and makes us colder

Scientists have discovered a set of nerve cells in the brain that are essential to our ability to sleep and control our body temperature.

The functioning of sleep in the human brain has remained largely a mystery. Some people seem to be able to fall asleep in an instant, while others take a lot longer.

Now, however, published research for Nature Communications by a team of scientists seems to confirm the discovery of the "sleep switch" of the brain, two decades after his first suggestion.

The team at the Department of Neurology at the Beth Israel Deaconess Medical Center in the United States has revealed that cells – located in a region of the hypothalamus called the Ventrolateral Preoptic Nucleus (VLPO) – are essential to our drift.

By working with genetically modified mice, the team artificially activated VLPO neurons with the help of several different tools. In one experiment, the team activated the neuronal cells with the help of a laser beam technique called optogenetics, which triggers them. In another test, the researchers used a chemical that selectively activates VLPO neurons.

In both tests, they discovered that they were crucial for falling asleep animals. This confirmed the previous findings of the team led by Clifford Saper that lesions of these neurons can cause insomnia.

Contradictory results

More interestingly, these results completely contradict another study published in 2017, which showed that the stimulation of VLPO neurons had the effect of making the mice alert.

In explaining this contradiction, Saper said, "We found that when VLPO cells are stimulated one to four times a second, they trigger each time they are stimulated, resulting in sleep.

"But if you stimulate them faster than that, they start not to shoot and end up shooting. We learned that our colleagues in the other lab stimulated the cells 10 times a second, which really shut them down. "

Another interesting discovery of the research is how VLPO neurons control body temperature – or, more precisely, how they make us colder when they are activated.

In mice, activation of VLPO resulted in a body temperature drop of up to six degrees Celsius. "We thought that was why people had to put themselves under a warm blanket to fall asleep," Saper said.

The team proposed that overuse of these same neurons is responsible for prolonged sleep and lower body temperature in hibernating animals.