Why does the urge to sleep become stronger the longer we stay awake? Scientists may have found an important part of the answer.
Researchers from the University of Basel, along with scientists from Beth Israel Deaconess Medical Center and Auburn University, have identified two groups of brain cells that appear to help build the body’s pressure to sleep.
Brain Cells Track Time Spent Awake
The researchers studied brain activity in mice during normal sleep and wake periods, as well as after extended sleep deprivation.
They discovered two populations of neurons in the brainstem GABAergic and serotonergic neurons whose activity increased the longer the animals remained awake.
Once sleep began, the activity of these neurons decreased. This suggests that the cells may be responding not simply to whether an animal is awake, but to how long it has been awake.
Activating the Cells Increased Sleep
Scientists then changed the activity of these neurons to determine whether they were actually driving sleep pressure.
When the cells were activated, the mice slept for longer and more deeply, resembling the recovery sleep that normally follows prolonged wakefulness.
When researchers inhibited the neurons, the animals slept considerably less. In experiments involving both groups of neurons, sleep was reduced by about 70%.
A New Clue About Sleep Pressure
The findings provide evidence that some neurons do more than simply register prolonged wakefulness. They may actively convert time spent awake into an increasing biological demand for sleep.
The discovery could help scientists better understand how the brain regulates sleep and why prolonged sleep loss eventually becomes difficult to resist.
What Comes Next?
The study was conducted in mice, so the findings do not yet establish that the same mechanism works identically in humans.
Researchers now want to understand how these neurons communicate with other parts of the brain and what molecular processes cause sleep pressure to build.
A better understanding of this system could eventually provide new clues about sleep disorders and the effects of long-term sleep deprivation.
