A University of Iowa study has found twitches made during sleep activate the brains of mammals differently than movements made while awake. Researchers say the findings show twitches during rapid eye movement (REM) sleep comprise a different class of movement and provide further evidence that sleep twitches activate circuits throughout the developing brain. In this way, twitches teach newborns about their limbs and what they can do with them.
UI graduate students Alexandre Tiriac and Carlos Del Rio-Bermudez say the findings of their new study provide further evidence that newborns learn about their bodies by twitching in their sleep.
“Every time we move while awake, there is a mechanism in our brain that allows us to understand that it is we who made the movement,” says Alexandre Tiriac, a fifth-year graduate student in psychology at the UI and first author of the study titled “Self-Generated Movements with “Unexpected” Sensory Consequences“, which appeared this month in the journal Current Biology. “But twitches seem to be different in that the brain is unaware that they are self-generated. And this difference between sleep and wake movements may be critical for how twitches, which are most frequent in early infancy, contribute to brain development.”
Mark Blumberg, a psychology professor at the UI and senior author of the study, says this latest discovery is further evidence that sleep twitches— whether in dogs, cats or humans—are connected to brain development, not dreams.
“Because twitches are so different from wake movements,” he says, “these data put another nail in the coffin of the ‘chasing rabbits’ interpretation of twitches.”
According to UI reporter Sara Agnew, researchers record no brain activity when a baby rat vigorously moves its left hindlimb while awake. While the left hindlimb of a sleeping baby rat twitches, researchers record the extensive activity in the area of the rat’s brain that is sensitive to twitches of that limb. “We noticed there was a lot of brain activity during sleep movements but not when these animals were awake and moving,” Tiriac says.