It goes without saying that we all need a good night's sleep to feel re-energized for the day ahead. But now, researchers have found that sleep also helps to boost reproduction of the cells involved in brain repair.
Scientists from the University of Wisconsin, Madison, have discovered that sleep increases the reproduction of cells that form myelin - the insulating material found on nerve cell projections in the brain and spinal cord.
Previous studies over the years have shown that numerous genes are switched on as we sleep and switched off during wakefulness. But according to the researchers, how sleep can affect certain types of cells was unknown.
They point to oligodendrocytes. These cells are responsible for making myelin within a healthy brain and in response to injury. The researchers add that myelin is responsible for allowing electrical impulses to move from cell to cell, "similar to insulation around an electrical wire."
They conducted a study in mice, analyzing gene activity of oligodendrocytes in the cerebral cortex of mice that slept, and then comparing these with the gene activity of mice that stayed awake.
Myelinated fibers in mouse cerebral cortex (myelin appears black in the left image, and green after segmentation in the right image) electron microscopy image.
Image credit: SBF-SEM; courtesy of Chiara Cirelli
Results showed that in the mice that slept, genes were turned on that triggered the formation of myelin. But in the mice that stayed awake, this triggered the genes involved in cell death and cellular stress response.
Additionally, further analysis showed that cells that become oligodendrocytes, called oligodendrocyte precursor cells (OPCS), double in reproduction during sleep. This reproduction is heightened during rapid eye movement (REM), which is linked to dreaming.
Chiara Cirelli, of the Center for Sleep and Consciousness at the University of Wisconsin, says:
"For a long time, sleep researchers focused on how the activity of nerve cells differs when animals are awake versus when they are asleep.
Now it is clear that the way other supporting cells in the nervous system operate also changes significantly depending on whether the animal is asleep or awake."
Dr. Cirelli notes that these findings may suggest that extreme or chronic lack of sleep could trigger some symptoms associated with multiple sclerosis (MS), a progressive brain disease associated with myelin damage. However, she adds that further studies are needed to determine whether this link exists.
Other studies have shown how sleep benefits brain function. Recent research from Brown University suggests that sleep helps our brains to better learn specific motor tasks, such as typing or playing the piano.
A 2012 study from the University of California, Los Angeles suggests that when asleep or under anesthetic, the brain acts as if it is trying to access memories.