By Tracy Brighten
Researchers identify that rapid eye movement or REM sleep, usually associated with dreaming, is critical to converting daytime experiences into memories required for normal brain function
Researchers say their findings help to explain how children’s learning is affected by inadequate REM sleep, and how medication commonly prescribed for hyperactivity or depression interferes with this sleep.
The infant years, as well as adolescence, are critical learning periods of synaptic plasticity, or remodelling, when sensory and motor skills, and cognitive function are developed. Sleep enhances this plasticity.
Previous studies have shown that infant mammals spend much of their time in REM sleep, but it was not understood how this type of sleep affected brain development and memory.
Led by neuroscientists Michelle Dumoulin Bridi, of University of Pennsylvania’s Perelman School of Medicine, and Marcos Frank, of Washington State University’s College of Medical Sciences, researchers investigated the function of REM sleep on brain development.
The role of REM sleep in visual development
Based on studies where sleep enhanced ocular dominance plasticity (ODP), this study, published in Science Advances, focussed on the role of REM sleep in visual development. Previously identified in children, ODP occurred after the delayed removal of a cataract when the seeing eye became dominant.
Study group kittens had a patch placed over one eye for six hours while they were active. Then they slept for one hour while their brain activity was monitored. One third of kittens were awakened during REM sleep phases only, another third during non-REM sleep phases, and the final third were left to sleep throughout.
The normal post-sleep enhancement of ocular dominance plasticity expected when vision was restricted in one eye was not seen in the group of kittens with interrupted REM sleep.
Waking experiences are consolidated during REM sleep
The study findings suggest that waking experiences are consolidated in the brain by molecular and network adaptations that take place during REM sleep. These changes are made permanent by the enzyme extracellular signal–regulated kinase, or ERK, which is only activated during REM sleep.
“Without REM sleep, permanent plastic changes to the visual cortex did not occur and the ERK enzyme did not activate,” said Frank. He compared REM sleep to the chemical developer in photographic film processing in making experiences more permanent and focused in the brain.
Researchers also discovered for the first time that brain activity patterns in the developing brain during REM sleep were similar to those occurring when awake.
REM sleep deprivation may affect learning
The study has important implications for understanding sleep in children and how sleep deprivation affects learning. The National Sleep Foundation recommends 14-17 hours per day for newborns, decreasing to 10-13 hours for pre-schoolers, and to 8-10 hours for 14-17 year olds.
Researchers acknowledged the importance of REM sleep to adolescents during a time of synaptic plasticity, and to adults for perceptual learning. Frank suggested REM sleep may have similar functions in other parts of the brain, not just the visual cortex, and across the life span.
Drugs can impact REM sleep
Frank suggests the findings may impact the use of prescribed drugs that affect brain activity and REM sleep, such as Ritalin and anti-depressant medications.
With REM sleep crucial to cementing cognitive function during sensitive learning periods, addressing both the duration and the quality of sleep is essential for normal brain development.
Image credit: Sweet Dreams by David Brighten
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