NEW YORK: As most every human has discovered, a couple nights of bad sleep is often followed by grogginess, difficulty concentrating, irritability, mood swings and sleepiness. For years, it was thought that these effects, accompanied by cognitive impairments like lousy performances on short-term memory tests, could be primarily attributed to a chemical called adenosine, a neurotransmitter that inhibits electrical impulses in the brain. Spikes of adenosine had been consistently observed in sleep-deprived rats and humans. Adenosine levels can be quickly righted after a few nights of good sleep, however. This gave rise to a scientific consensus that sleep debt could be forgiven with a couple of quality snoozes — as reflected in casual statements like “I’ll catch up on sleep” or “I’ll be more awake tomorrow.”
But a review article published recently in the journal Trends in Neurosciences contends that the folk concept of sleep as something that can be saved up and paid off is bunk. The review, which canvassed the last couple of decades of research on long term neural effects of sleep deprivation in both animals and humans, points to mounting evidence that getting too little sleep leads to long-lasting brain damage and increased risk of neurodegenerative disorders like Alzheimer’s disease.
“This is really, really important in setting the stage for what needs to be done in sleep health and sleep science,” said Mary Ellen Wells, a sleep scientist at the University of North Carolina, who did not contribute to the review. It has long been known that intense periods of sleep deprivation are bad for your health. Forced insomnia was used for centuries as punishment and torture. But there are many ways to not get enough sleep. You can go entirely without sleep for an extended period of time — what scientists call acute sleep deprivation. (In 1963, a high school student managed to stay awake for 264 hours.) You can consistently miss out on sleep — chronic sleep deprivation. You can lie awake, mind racing, or relax, watching television all night. Research continued, but “that was where it was sort of pigeonholed,” said Fabian Fernandez, a neuroscientist at the University of Arizona who did not contribute to the new review. “When are you ever going to keep an animal or human awake until they die?”
Over the past couple of decades, however, the animal research on sleep deprivation has become more nuanced, precise and, possibly, applicable to humans, according to Dr. Sigrid Veasey, a neuroscientist at the University of Pennsylvania, and Zachary Zamore, a researcher in Dr. Veasey’s lab, the authors of the new review.
After surveying past studies of sleep-deprived mice, many of which Dr. Veasey conducted, the researchers found that when the animals were kept awake for just a couple of hours more than usual each day, two key parts of the brain were notably affected: the locus coeruleus, which manages feelings of alertness and arousal, and the hippocampus, which plays an important role in memory formation and learning. These regions, which, in humans, are central to sustaining conscious experience, slowed down the animals’ production of antioxidants, which protect neurons from unstable molecules that are constantly being produced, like exhaust fumes, by functioning cells. When antioxidant levels are low, these molecules can build up and attack the brain from inside, breaking down proteins, fats and DNA.
“Wakefulness in the brain, even under normal circumstances, incurs penalties,” Dr. Fernandez said. “But when you’re awake for too long, then the system gets overloaded. At some point, you can’t beat a dead horse. If you’re asking your cells to remain active for 30 percent more time each day, cells die.”
Whang is a journalist with NYT©2022
The New York Times