You must have heard and read that sleep helps strengthen and consolidate memories. Now, researchers show how it works.
Sleep after learning encourages the growth of dendritic spines - the tiny protrusions from brain cells that connect to other brain cells and facilitate the passage of information across synapses.
Moreover, the activity of brain cells during deep sleep, or slow-wave sleep, after learning is critical for such growth, say researchers from NYU Langone Medical Centre, New York.
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The findings in mice show for the first time how learning and sleep cause physical changes in the motor cortex, a brain region responsible for voluntary movements.
"Here, we have shown how sleep helps neurons form very specific connections on dendritic branches that may facilitate long-term memory. Learning causes very specific structural changes in the brain," said senior investigator Wen-Biao Gan.
Using a special laser-scanning microscope that illuminates the glowing fluorescent proteins in the motor cortex, the scientists tracked and took images of dendritic spines along individual branches of dendrites before and after mice learned to balance on a spin rod.
Over time, mice learned how to balance on the rod as it gradually spun faster.
Researchers trained two sets of mice: one trained on the spinning rod for an hour and then slept for seven hours.
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The second trained for the same period of time on the rod but stayed awake for seven hours.
The scientists found that the sleep-deprived mice experienced significantly less dendritic spine growth than the well-rested mice.
Furthermore, they found that the type of task learned determined which dendritic branches spines would grow, said the study published in the journal Science.