New research out of Boston University's Department of Biomedical Engineering shows that our brains are actually taking a bath in cerebrospinal fluid (CSF) while we are in deep, non-REM, sleep, cleaning away toxins and waste products.
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Professor Laura Lewis is the study's co-author and explains how these findings can offer insight into conditions often associated with sleep disorders, such as autism and Alzheimer's.
Volunteers were monitored in MRI scanners and Prof Lewis said the researchers noticed something interesting about the movement of CSF in the brain.
“And what we realised when we were imaging it that when people went into non-REM sleep, they would start to have really large waves of CSF that would come about once every 20 seconds, at a higher velocity than you would ever typically see when they were awake.
“The other thing we realised is that these waves of CSF were coupled to waves of electrical activity in the brain and to changes in blood volumes.”
This indicates, she says, that the electrical activity of the brain, the blood of the brain, and its CSF are all undergoing waves that are linked together during sleep. The wave imagery is useful to understand what’s happening in the brain while we sleep, she says.
“Every few seconds we see this wave flowing in, we actually weren't able to measure whether it comes out again, my presumption is that it does, but what we were able to image is certainly that at least it's flowing upwards into the brain.”
This ‘washing’ activity that happens during deep sleep could be neuron activity, she says.
“Our data suggests that the reason might be partly because when people are in the stage of sleep, there are periods lasting a few hundred milliseconds where the neurons go quiet. And after they go quiet, there's a decline of blood volume in the brain.
“And so we think that as there's less blood in the brain, it might leave more space for fluid to flow upwards in the brain to occupy the space that's been freed.”
Laura Lewis Photo: Boston University
The research could have future implications for treating neurodegenerative disorders, she says.
“We know from other people's studies that people who are in the early stages of neurodegenerative disorders such as Alzheimer's Disease actually have fewer of these electrical waves in the neurons during sleep, and they also have lowered blood flow to the brain.
“And so if the same thing we saw here is also true in those populations, then that would suggest that maybe they may not have as much of these CSF waves. We're extremely interested to test this idea.”
