Inside a series of tubes in a bright, warm room at Harvard Medical School, hundreds of fruit flies are staying up late. It has been days since any of them have slept: The constant vibrations that shake their homes preclude rest, cling as they might to the caps of the tubes for respite. Not too far away in their own tubes live other sleepless flies, animated with the calm persistence of those consigned to eternal day. A genetic tweak to certain neurons in their brains keeps them awake for as long as they live.
They do not live long. The shaken flies and the engineered flies both die swiftly — in fact, the engineered ones survive only half as long as well-rested controls. After days of sleeplessness, the flies’ numbers tumble, then crash. The tubes empty out. The lights shine on.
We all know that we need sleep to be at our best. But profound sleep loss has more serious and immediate effects: Animals completely deprived of sleep die. Yet scientists have found it oddly hard to say exactly why sleep loss is lethal.
Sleep is primarily seen as a neurological phenomenon, and yet when deprived creatures die, they have a puzzlingly diverse set of failures in the body outside the nervous system. Insufficient sleep in humans and lab animals, if chronic, sets up health problems that surface over time, such as heart disease, high blood pressure, obesity and diabetes. But those conditions are not what slays creatures that are 100% sleep deprived within days or weeks.
What does sleep do that makes it deadly to go without? Could answering that question explain why we need sleep in the first place? Under the pale light of the incubators in Dragana Rogulja’s lab at Harvard Medical School, sleepless flies have been living and dying as she pursues the answers.
On a cold morning this winter, Rogulja leaned over a tablet in her office, her close-cropped dark hair framing a face of elfin intensity, and flicked through figures to explain some of her conclusions. Rogulja is a neuroscientist and a developmental biologist by training, but she is not convinced that the most fundamental effect of sleep deprivation starts in the brain. “It could come from anywhere,” she said, and it might not look like what most people expect.
She has findings to back up that intuition. Publishing today in the journal Cell, she and her colleagues offer evidence that when flies die of sleeplessness, lethal changes occur not in the brain but in the gut. The indigo labyrinths of the flies’ small intestines light up with fiery fuchsia in micrographs, betraying an ominous buildup of molecules that destroy DNA and cause cellular damage. The molecules appear soon after sleep deprivation starts, before any other warning signs; if the flies are allowed to sleep again, the rosy bloom fades away. Strikingly, if the flies are fed antioxidants that neutralize these molecules, it does not matter if they never sleep again. They live as long as their rested brethren.
The results suggest that one very fundamental job of sleep — perhaps underlying a network of other effects — is to regulate the ancient biochemical process of oxidation, by which individual electrons are snapped on and off molecules in service to everything from respiration to metabolism. Sleep, the researchers imply, is not solely the province of neuroscience, but something more deeply threaded into the biochemistry that knits together the animal kingdom.
More Fatal Than Starvation
The first studies to investigate total sleep deprivation had a maniacal quality to them. In Rome in 1894, Maria Mikhailovna Manaseina, a Russian biochemist, made a presentation at the International Congress of Medicine about her experiments on 10 puppies. She and her lab assistants had kept the dogs awake and in constant motion 24 hours a day; within about five days, all the puppies had died. Sleep deprivation seemed to kill puppies much more quickly than starvation, she reported: “The total absence of sleep is more fatal for the animals than the total absence of food.”
Autopsies revealed that the puppies’ tissues were in bad repair, particularly in the brain, which was rife with hemorrhages, damaged blood vessels and other gruesome features. Sleep, Manaseina concluded, is not a useless habit. It does something profound for brain health.
More all-day, all-night dog walking followed. In 1898 Lamberto Daddi, an Italian researcher, published detailed drawings of the brains of dogs that had been sleep-deprived; he reported apparent degenerative damage in the brain, similar to that seen in dogs that had faced other stressors. Around the same time, the psychiatrist Cesar Agostini kept dogs in cages rigged with bells that jangled horribly whenever they tried to lie down and sleep, and in the 1920s researchers in Japan did something similar with cages studded with nails.
The studies, aside from their consistent cruelty, had a similar weakness: They had no valid controls. The dogs had died and their tissues looked abnormal — but was that truly because they had not slept? Or was it because nonstop walks and stimulation are inherently stressful? Separating the effects of sleeplessness from being kept on your feet until it killed you seemed impossible.
The Turntable Cage
It took decades for scientists to return to the question in a serious way. In the 1980s, Allan Rechtschaffen, a sleep researcher at the University of Chicago celebrated for his pioneering work on narcolepsy, began to design experiments that could separate the effects of overstimulation from those of sleeplessness. He devised a rat cage in the form of a turntable suspended over water. A divider ran down the middle, so animals could live on either side while the turntable floor beneath them spun freely. Into the device the experimenters put pairs of rats, one of which was destined to be denied sleep. Whenever that rat tried to rest, the scientists spun the table, nudging both rats awake and sometimes pushing them into the water.
This setup ensured that although both rats fell into the water equally often, the control rat could still catch some winks whenever the rat denied sleep was active. In fact, control rats managed to sleep about 70% as much as they normally would, suffering only mild sleep deprivation. The unluckier experimental rats got less than 9%, almost total sleep loss.
Both sets of rats were disturbed the same number of times. Both suffered the stress of falling into the water and having to clamber back out, dripping. But only the severely sleep-deprived rats began to decline. Their fur grew rough and disheveled, and it went from white to a mangy yellow. They developed lesions on their skin. They lost weight. After around 15 days on average, they died. Rechtschaffen had discovered a way to show that sleep loss itself really did kill.
For the graduate students running these experiments, the days were long. “The lab was in an apartment building, so you’d have a bedroom next to an animal testing room,” said Ruth Benca, a professor of psychiatry at the University of California, Irvine who worked with Rechtschaffen for some years. “They had bedrooms next to the rooms where their animals were being deprived so they could monitor around the clock.”