Although we spend half our lives doing it, scientists still aren’t sure exactly how we go to sleep or why nature has decided that all animals should do it.
Researchers from Oxford University have further narrowed the search by subjecting poor fruit flies to sleep deprivation and discovering in the process the molecules that regulate a handful of sleep-promoting neurons in the brain.
Once the molecules act on the neurons, they fire off, telling the brain that we’re tired and need to sleep.
This bundle of neurons, which has been claimed as the elusive “sleep switch” that controls when we drop off and when we wake up, was first discovered in 2011 by a Washington State University study of fruit flies published in Science.
One of the authors of that study, Dr Jeff Donlea, has since joined the lab of Professor Gero Miesenboeck in Oxford, where they have continued to explore the neurons in the brains of flies, although they believe the same mechanism could be present in our own brains.
“There is a similar group of neurons in a region of the human brain,” Donlea said. “These neurons are also electrically active during sleep and, like the flies’ cells, are the targets of general anaesthetics that put us to sleep. It’s therefore likely that a molecular mechanism similar to the one we have discovered in flies also operates in humans.”
Discovering the biological proteins that affect the sleep switch could help in coming up with new drugs to combat sleep disorders like insomnia, but it also takes researchers a step closer to solving the deeper mysteries of sleep.
“The big question now is to figure out what internal signal the sleep switch responds to,” said Dr Diogo Pimentel of Oxford University, another lead author of the study. “What do these sleep-promoting cells monitor while we are awake?”
“If we knew what happens in the brain during waking that requires sleep to reset, we might get closer to solving the mystery of why all animals need to sleep.”
To find this molecular switch, the team subjected the fruit flies to what Professor Miesenboeck jokingly referred to as a “Zero Dark Thirty type of experiment”.
“We forcefully kept flies from sleeping by rattling them for a whole night and then measured whether they slept more during the following day,” he explained. “Normal flies caught up on their lost sleep (like you and I would after an all-nighter), but the mutants couldn’t.”
In these mutant flies, a key molecular component of the electrical activity switch was broken, keeping the sleep-inducing neurons in the always-off position and causing insomnia.