sleeping memoryScientists have long suspected that sleeping was crucial to the learning and memory-building process, but a new study provides important evidence on how sleep impacts the brain, indicating our minds are hard at work while our bodies rest.

The research, published recently in the journal Science, shows that very specific structural changes happen in the brain after a period of learning. In essence, our brains practice what they’ve just learned while we are in various stages of a night’s sleep.

Using mice, the researchers discovered that during sleep, the brain grows new connections between cells in the motor cortex. These brain cells essentially awaken as we enter slow-wave sleep, when brain waves slow down and rapid eye movement and dreaming stop.

“Here we’ve shown how sleep helps neurons form very specific connections on dendritic branches that may facilitate long-term memory,” explains Wen-Biao Gan, senior investigator and professor of neuroscience and physiology at NYU Langone Medical Center. “We also show how different types of learning form synapses on different branches of the same neurons, suggesting that learning causes very specific structural changes in the brain.”

Using genetically-modified mice, made so that a particular protein lights up when looked upon with a laser-scanning microscope, the scientists were able to track the growth of these new pathways.

In the first stage of research, the scientists trained the mice to balance on a spin rod. They eventually learned to maintain that balance as the rod spun faster and faster. Then, observing their brain activity, the scientists noted the mice “sprouted new dendritic spines within 6 hours” of their training session.

Next, the researchers looked more closely at the effects of sleep. They trained two groups of the mice on the rod. One group trained for an hour followed by seven hours of sleep. The other group trained for an hour but were kept awake for the following seven.

Those that slept saw significantly more dendritic spine growth than those kept awake. They also noted that different types of training resulted in different dendritic spine pathways. For instance, running forward produced different changes than running backwards.

“Imagine a tree that grows leaves (spines) on one branch but not another branch,” explains Gan, “When we learn something new, it’s like we’re sprouting leaves on a specific branch.”

This research joins the countless studies on the importance of getting adequate sleep, such as one study showing how toxic waste is removed from the brain during sleep. When learning a new task or studying new information, the need for a good night’s sleep is especially crucial, indicating all-night study sessions may be an exercise in futility for students around the world.


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