New research from Boston University suggests that something extraordinary happens in our brains every night while we sleep. Once fallen into the arms of Morpheus, the neurons cease their ordinary activity and reach a state of rest. Shortly thereafter, the blood gives way to a watery fluid called cerebrospinal fluid (CSF), which normally surrounds the brain and spinal cord and flows through the brain in rhythmic, pulsating waves. The blood may flow away probably because the “switched off” neurons need less oxygen.
The study, published in Science, is the first to demonstrate that the brain’s CSF pulsates during sleep and that these movements are closely related to brain wave activity and blood flow. “We’ve known for a long time that there are these electrical waves of activity in neurons,” says study co-author Laura Lewis, an assistant professor of biomedical engineering in the BU College of Engineering and a faculty member of the Center for Systems Neuroscience. “But before now, we didn’t realize that there are actually waves in the CSF as well.” This research may also be the first study ever to image CSF during sleep. And Lewis hopes it will one day lead to insights into a variety of neurological and psychological disorders that are often associated with disrupted sleep patterns, including autism and Alzheimer’s disease.
As the research progresses, Lewis’s team has another puzzle they want to solve: How exactly do our brain waves, blood flow, and cerebrospinal fluid coordinate so perfectly with each other? “We see that the neuronal change always seems to happen first, and then it’s followed by a rush of blood out of the head, and then a surge of CSF in the head,” Lewis says.