An organized tide of brain waves, blood and spinal fluid pulsing through a sleeping brain may flush away neural toxins that cause Alzheimer’s and other diseases.
Quanta Magazine said:When you sink into a deep sleep, a cycle of activity starts behind your closed eyelids. First, a slow electrical wave pulses through the brain. A few seconds later, the amount of blood within the brain drops. Then a wave of cerebrospinal fluid reverses its usual direction of flow and moves upward through large cavities in the lower and central portions of the brain. The pattern repeats about three times a minute for the duration of non-REM sleep, the typically dreamless phases when your eyes remain still.
In a recent study, researchers observed the rhythmic sequence uniting these three phenomena in humans for the first time and found the causal links between them. Their finding clarifies how sleep may protect the brain’s well-being by driving elements of an obscure “plumbing system” found in the brain only a few years ago. Someday, the newly discovered mechanism might be the basis for new treatments to prevent cognitive decline in patients with Alzheimer’s disease and other conditions, but it’s already of value for deepening understanding of the physiological dynamics of sleep.
Sleep is a rather surreal phenomenon, says Laura Lewis, an assistant professor of biomedical engineering at Boston University and the senior author on the study. Every day, we enter an altered state of consciousness in which many aspects of our cognition and physiology change dramatically and simultaneously. Yet we can’t live without it. Animals deprived of sleep die, and even insufficient sleep is linked to cognitive decline.
For years, scientists have suspected that the harm caused by disturbed sleep has something to do with an overaccumulation of waste products or toxins in the brain. Studies showed that sleep is important for waste clearance, but the specifics were foggy. In 2012, research in the laboratory of Maiken Nedergaard, a neuroscientist at the University of Rochester Medical Center, identified what appears to be the brain’s waste clearance pathway, the glymphatic (glial-lymphatic) system. This is a thin set of channels formed by the brain’s glial cells that can conduct fluid within the brain. The problem was that no plausible mechanism seemed to connect the neurological signs of sleep with the glymphatic system or even with movements of the cerebrospinal fluid (CSF) more generally. “We just weren’t sure what was changing, or how,” Lewis said.
Animal experiments did hint, however, that there was some correlation between sleeping brain wave activity and the flow of fluids through the brain. Looking for those patterns in sleeping human brains seemed like a good way to start getting some answers.
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