Sleep has benefits beyond making people feel rested. Research from New York University’s Langone Medical Center found that sleeping after learning supports the growth of certain brain connections. The study is the first to demonstrate that sleeping after learning results in physical changes in the brain. The findings contribute to the body of evidence indicating that sleep is critical for both children and adults.
The study was based on the long-standing hypothesis that sleep is critical for forming and recalling memories. Seeking physical evidence for sleep’s role in learning and memory, the researchers conducted a study with mice that were genetically engineered to have a fluorescent protein in their neurons. The researchers used a special laser-scanning microscope to illuminate the fluorescent protein and track neuronal growth in the brain’s motor cortex. This allowed them to monitor the growth of particular brain connectors—dendrites—while the mice learned how to balance on a spin rod.
Dendrites branch off neurons, growing towards other neurons to form connections. The dendrites the researchers observed in this study further branched into spines. The researchers tracked the growth of the dendritic spines as the mice honed their skills on the spin rod. After noting that the mice grew new spines on their dendritic branches within six hours after training, the researchers split the mice into two groups. One group of mice trained for an hour then slept for seven hours. The other group of mice trained for an hour then stayed awake for seven hours.
The mice forced to stay awake after practicing on the spin rod had significantly less dendritic growth than the mice who were allowed to sleep afterwards. From this, the researchers conclude that sleep encourages the growth of dendritic spines, helping the brain cement connections between neurons and facilitating learning and memory. When the mice slept, the same cells that were active during their practice sessions reactivated, spurring dendritic growth.
The researchers also found that the type of task determined which dendritic branches grew. Since the mice practiced a physical task, the researchers saw growth in the motor cortex.
This study indicates that both learning and sleep cause physical chances in the brain. Furthermore, a lack of sleep can inhibit the ability to learn and limit the formation of long-term memory.
This research is published in the journal Science.
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