The body may not need sleep so much, but the brain sure does: a huge amount of housekeeping is done while we’re sleeping, and losing sleep, especially chronically, prevents this essential work. Two new studies illustrate what sleep loss does to our thinking skills the next day and to the brain’s ability to clear out potentially dangerous “gunk.”
The first study, from Michigan State University, had 77 people stay awake all night in the lab and 63 go home and sleep normally. All the participants were rested before the study began, and then separated into their respective groups for one night of sleep deprivation or normal rest. The researchers gave them tests of attention (the Psychomotor Vigilance Task) and cognition (the UNRAVEL method, which involves having to keep track of a series of steps in the face of period interruptions) in the evening and again the following morning.
The sleep-deprived participants did conspicuously worse on the tests than the rested ones: The evening before, there was about a 15% error rate after interruptions on the UNRAVEL test, which the next morning rose to 30%. In contrast, the rested group performed about the same in the evening before and the morning after. The sleep-deprived also had significantly more lapses in attention the morning after, compared to the rested group.
“Our research showed that sleep deprivation doubles the odds of making placekeeping errors and triples the number of lapses in attention, which is startling,” said study author Kimberly Fenn in a statement. “Sleep-deprived individuals need to exercise caution in absolutely everything that they do, and simply can’t trust that they won’t make costly errors. Oftentimes – like when behind the wheel of a car – these errors can have tragic consequences.”
Not every task we do may suffer from sleep deprivation, but many do, and across many areas. “[S]leep deprivation causes widespread deficits across all facets of life,” Fenn said.
While this study shows how sleep deprivation can lead to cognitive effects almost immediately, the next looks at how sleep deprivation can put a person at risk for more serious problems, like cognitive decline and dementia, over the longer term.
In the second study, from Boston University, researchers were able to observe the “behavior” of cerebrospinal fluid (CSF) in the brain as people slept. The team wanted to figure out whether brain wave activity correlated with blood flow and CSF flow—so they had people wear EEG caps to measure brain waves, and fall asleep inside an MRI machine to observe the movement of the two fluids.
What they found was really neat: as brain cells quieted down and brain waves slowed during sleep, blood moved out of the brain—and as it did, CSF entered and “pulsed” in waves.
“We do see that the neural change always seems to happen first, and then it’s followed by a flow of blood out of the head, and then a wave of CSF into the head,” said Lewis. “It’s such a dramatic effect.”
Previous work has shown that brain waves change during sleep, of course, and other work has shown that CSF flows in to flush out debris, including proteins known to accumulate in Alzheimer’s disease, but no one had observed the connectivity of the two phenomena till now. Other, observational studies have shown that lack of sleep is correlated with risk for neurological diseases including Alzheimer’s.
The new studies tie together nicely several lines of early work—and again, while they each look at different aspects and timescales of sleep deprivation, they’re good reminders that losing sleep can have serious effects, in the short and long terms.