Right Now in Sleep Science

Imaging the Sleeping Brain

The brain continues to work while we sleep, consolidating memories, "cleaning" itself, and maintaining our metabolism and other critical systems of our body.

Until recently much of how the brain works during sleep has been speculative. Dr. Laura Lewis, a scientist from MIT and Massachusetts General Hospital, has found a way to measure blood and fluid flow in the brain. By using EEG and fMRI, which measures oxygen levels in blood and watching the cerebrospinal fluid (CSF), Dr. Lewis has determined that our brains flush out fluid while we sleep. CSF flow pulsates with heartbeat and breathing, but what was discovered is that CSF flows at a much higher rate while we sleep, carrying with it any toxic proteins picked up during the day.

One example of this is "amyloid", a protein that has been linked to Alzheimer’s disease, and flows out at a much higher rate while sleeping. Lack of sleep can cause toxic proteins to build and in turn hamper the ability to think clearly and to sleep well.

So, if high CSF flow is good, can it be stimulated when people are awake? By the same process, using EEG and fMRI, it was determined that CSF flow does increase with brain stimulation. However, the increased rates were significantly less than when asleep. Sleep is the optimal state for clearance: neural activity slows and there is a change in respiratory and vascular oscillations which opens the way for cerebrospinal fluid flow.