Desynchronizing monkeys’ brain with electricity caused a performance boost
What if we could obtain the memory, learning and perception benefits of “power naps” without actually sleeping?
A recent study in Science suggests that at least some of our primate cousins can. Researchers showed that brief naps (without rapid eye movement, or REM, sleep) improved macaques’ performance on a visual-perception task. The scientists then reproduced this boost by electrically stimulating the brains of awake monkeys in a way that mimicked sleeping brain activity—inducing a kind of “artificial nap.” The process, if effective in humans, might one day help boost cognition and treat sleep disorders.
The team first trained five monkeys on a task evaluating image orientations and tested them twice, with a 30-minute gap in which they either had non-REM sleep or merely rested. The monkeys that slept performed significantly better on the second test. The researchers recorded thousands of neurons’ activity in three brain regions: two visual areas and one associated with decision-making. In the monkeys that slept between tests, this activity was, oddly, less synchronized during the second task than the first.
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“Sleep is a synchronizing phenomenon in which neurons go up and down together, but the level of synchrony after sleep is reduced compared with before,” says the study’s senior author, Valentin Dragoi, a systems neuroscientist at Rice University. “This is surprising.” The size of this “desynchronizing” effect correlated with performance increases, suggesting that neurons firing more independently of one another may drive the improvement.
Low-frequency “delta” brain waves are known to be involved in memory maintenance. These waves dominated the monkeys’ sleeping brain activity, and the team wondered whether they were behind the performance boost. To test it, the researchers conducted the experiment again—but instead of letting the monkeys sleep, they stimulated a visual brain region using a low-frequency electrical signal that mimicked delta waves. This stimulation also led to both reduced neural synchrony and better performance.
These findings imply that brain stimulation could deliver some of the benefits of naps without sleep. The results in primates strongly suggest “artificial nap” effects will translate to humans, says Sara Mednick, a neuroscientist at the University of California, Irvine, who studies the relation between napping and performance; evidence already exists that electrical stimulation during sleep can benefit humans’ memory. “This work demonstrates that stimulating [when awake] at the delta frequency can mimic sleep benefits,” Mednick says.
The researchers used electrodes placed in the monkeys’ brains for stimulation, but they plan to test noninvasive techniques in people with sleep disorders “in the near future,” Dragoi says. They also plan to study other senses, cognitive functions and brain regions, he adds. “Are different areas most effective for particular tasks? No one knows.”