Researchers at the Washington University School of Medicine have found that when it is time to adapt to a challenging situation, fruit flies go to sleep. The discovery is shedding new light on how sleep may be used as a tool to cope with difficult circumstances.
“We know that sleep is involved in creativity and insight,” said study senior author Dr. Paul Shaw. “Have you ever slept on a problem, and when you wake up you’ve found the answer? Anxiety keeps people up at night, but if you find yourself in a dangerous environment, or in a situation that you don’t know how to deal with, sleep may be exactly what you need to respond to it effectively.”
The sleeping patterns of fruit flies are very similar to those in humans. The baby flies need a lot of sleep, but require less sleep as they get older. Fruit flies become alert under the influence of caffeine, yet drowsy under the influence of antihistamines. Furthermore, if you interrupt a fruit fly’s sleep one day, the fly will sleep longer the next.
All of these similarities suggest that the sleep habits of fruit flies can be used to predict the sleep habits of humans.
In an effort to investigate the relationship between difficult circumstances and sleep, the researchers took away flight ability in some fruit flies.
If baby flies do not expand their wings in the first half hour after emerging from a pupal stage, their wings do not develop properly. The researchers used a couple of methods to prevent newly emerged flies from expanding their wings, which left them flightless. The team also took away flight ability in older flies by disabling their wings.
Regardless of why or at what age the flies lost the ability to fly, they were all found to sleep more than usual when faced with the difficult circumstances.
The researchers traced the neurological circuit that alerted the brain to the issues and induced more sleep.
“When we identified the neurons that were activated when we cut or glued the wings of adult flies, they turned out to be the same neurons involved in the normal developmental process of wing expansion after emergence,” explained study first author Dr. Krishna Melnattur.
According to the researchers, the fact that wing injury and normal wing development are linked to sleep through the same neurological circuitry makes sense from an evolutionary standpoint. The circuit is active in young flies because their developing brains need sleep as the animals expand their wings, learn to fly, and begin to navigate a new world.
“And then the whole circuit can get reactivated later in life when something happens that forces a fly to adapt to a new normal,” said Dr. Shaw. “Suddenly, its brain needs to be as flexible as when it was young. It can no longer fly, but it still needs to get food, it needs to compete for mates, it needs to avoid dying. We think that sleep amplifies the brain plasticity the fly needs to survive.”
Next, the experts will investigate whether additional sleep helps flightless flies survive. The study may provide insight into why some people sleep more than others and why certain sleep disorders arise.
“There’s huge variation in sleep time among people. Some people need five hours a night; some need nine,” said Dr. Shaw. “Sleep is an ancient process, and we’ve evolved mechanisms to change our sleep-wake balance to help us meet our needs.”
“If these mechanisms get inappropriately activated, say by a traumatic event that triggers post-traumatic stress disorder, it can create a situation in which you’re sleeping too much or too little and it’s no longer matching up with your needs, and then you have a sleep disorder.”
The study is published in the journal Science Advances.