End to the mystery: why we all get tired at the end of the day?

A new study from the University of Basel, in collaboration with Beth Israel Deaconess Medical Center and Auburn University, identified groups of nerve cells in the brains of mice that measure the duration of wakefulness and activate the sleep drive. Artificial activation of these cells induced deeper sleep; their inhibition reduced sleep by 70% without severe behavioral impairment. The researchers hope the findings will lead to treatments for sleep disorders and resistance to sleep deprivation.

A new study published in the journal Nature has identified the brain mechanism responsible for the cumulative feeling of fatigue during the day, known as the "sleep drive." A team of researchers from the University of Basel in Switzerland, in collaboration with Beth Israel Deaconess Medical Center in Boston and Auburn University, located two separate populations of nerve cells in the brainstem of mice. The activity of these cells increased the longer the animals remained awake and decreased with sleep. In a crucial experiment, artificial activation of the cells caused the mice to sleep longer and deeper, similar to recovery sleep after sleep deprivation. Conversely, inhibiting the cells' activity reduced the need for sleep by about 70% of normal, and surprisingly, the mice did not suffer from the severe behavioral impairments that usually accompany such severe sleep deprivation. According to the head of the research team, Prof. Alex Shire, the cells do not just report fatigue but actively produce the sleep drive. The researchers hope that understanding this neural circuit will lead in the future to new treatments for sleep disorders and an understanding of how the brain copes with sustained wakefulness and load.