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Study: Brains, bodies of babies active during new sleep stage

Synchronized brain spindles and muscle twitching during a new phase of sleep help infants strengthen brain-body communication and coordination. Photo by PublicDomainPictures/Pixabay
Synchronized brain spindles and muscle twitching during a new phase of sleep help infants strengthen brain-body communication and coordination. Photo by PublicDomainPictures/Pixabay

June 16 (UPI) -- New research suggests infants use a newly discovered sleep phase to develop brain-body communication and coordination.

For years, scientists at the University of Iowa have been analyzing the twitching movements performed by infants during REM sleep. But during a recent study, researchers realized babies also exhibit muscle twitching outside of REM sleep.

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In fact, scientists found infants experience an increase in twitching movements during a previously unidentified sleep stage called quiet sleep.

Researchers detailed the discovery of the second major sleep stage in a new paper, published Wednesday in the journal Current Biology.

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"This was completely surprising and, for all we know, unique to humans and human infants," study co-author Mark Blumberg said in a press release.

"We were seeing things that we could not explain, based on our years of observation in baby rats and what's available in the scientific literature," said Blumberg, professor psychological and brain sciences at Iowa.

For the study, scientists recorded the twitching movements of 22 infants, ranging in age from one week to seven months, as they slept.

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The recordings showed the infants continue to twitch their limbs outside of REM sleep.

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"The twitches looked exactly the same," said lead author Greta Sokoloff, research scientist psychological and brain sciences department at Iowa.

"We did not expect to see twitches during quiet sleep -- after all, quiet sleep got that name because humans and other animals typically don't move during that state," Sokoloff said.

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In addition to recording their muscle movements, scientists also measured neural activity in the brains of the sleeping babies.

The data showed that during quiet sleep, infants exhibit sizable brain oscillations, known as sleep spindles, every 10 seconds.

Researchers found sleep spindles begin to increase around three months old, and that these oscillations are concentrated around a section of the brain's cortex called the sensorimotor strip, which processes sensory and motor information.

The oscillations and muscle twitches are neatly synchronized.

"Sleep spindles have been widely linked with learning and memory," Sokoloff said. "So our findings suggested to us that what the infants are doing is learning about their bodies through twitching during a period of sleep that we previously thought was defined by behavioral silence."

The authors of the new study suggest they've discovered an important new phase of development for brain-body communication and coordination.

"Our finding could reflect something important about the cortical contributions to motor control. Infants have to integrate the brain with the body, to get the system set up and working properly. It's not all connected at birth," Blumberg said.

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"There's a lot of development that has to happen after birth. What we think we're seeing is a new mode of integration among different parts of the brain and the body," Blumberg said.

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