Sleep is beginning to give up its secrets. A new study has provided some interesting insights into how sleep “cleans” the brain, Scientific American reports. Furthermore, the study sheds light on how sleep affects neurodegenerative diseases like Alzheimer’s as well as psychiatric disorders.
Sleep is a mysterious function. However, one area of slumber that is well-understood involves memory. Steady electrical oscillations called slow waves archive short-term memories into long-term storage. These electric pulses take place during non-REM, deep sleep. As the researchers discovered, slow waves appear to be connected to the movement of cerebrospinal fluid (CSF), one of the main cleaning solutions that the brain uses.
Cleanup in Ventricle Four
The team, led by Boston University neuroscientist Laura Lewis, wasn’t quite sure exactly how CSF rejuvenates the brain. They did, however, find evidence that slow waves flushed both blood and CSF throughout the brain by observing the fourth ventricle.
Their research points to a connection between sleep disturbances and neurodegenerative and psychiatric afflictions. The hope is that the team’s findings might lay the groundwork for new ways of diagnosing and treating such disorders.
“We’ve discovered there are really large waves of CSF that appear in the brain only during sleep,” Lewis told Scientific American. “This effect is really striking, and we’re also interested in what it means for maintaining brain health, especially in disorders such as Alzheimer’s disease.”
To make the discovery, the team looked at how the flow of CSF changes during sleep. Lewis and her team also wanted to know how CSF dynamics related to blood flow and electrical activity in the brain.
The study, published in the journal Science, began with the team monitoring the brain waves of 13 healthy sleeping adults. They used two types of technology in this endeavor. The first was electroencephalography (EEG). The second involved a variation of fMRI technology called “accelerated fMRI.” This cutting edge tech captures images of the brain faster than a conventional fMRI machine.
Interestingly, the team had a major breakthrough because of a flaw in the fMRI. The researchers found that they could only see CSF movement when they also monitored blood flow. This was because the machine clocked all new fluids arriving in the brain.
“We realized we could take advantage of this to measure CSF flow at the same time as blood oxygenation,” Lewis said. “That was critical, because it turns out these things are coupled to each other in a way we never would have seen if we didn’t measure blood, CSF and electrical activity simultaneously.”
By observing the brain’s electrical activity, the researchers discovered that slow waves directly corresponded to CSF and blood flow. Computer models seemed to confirm the relationship between these three neurological functions. The major breakthrough, however, is the discovery that, as blood flowed to electrically active places in the brain and then flowed away again, CSF followed it. In other words, electrical activity influences blood flow, which in turn affects CSF.
This is an important finding in the fight against Alzheimer’s. Scientists think that the disease attacks after a critical mass of toxins is left behind in the brain. Lewis is hopeful that monitoring CSF flow might show promise as a diagnostic tool. Meanwhile, electronic stimulation may one day help flush CSF through a patient’s brains to actually treat Alzheimer’s.