The researchers found that during deep sleep, the internal brainwaves can initiate a cleansing system within the brain that can protect against Alzheimer's disease and other neurodegenerative brain diseases. The study entitled "Electrophysiological, hemodynamic and cerebrospinal fluid oscillations in human sleep" was published this week in the latest issue of the journal. Science.
MRI image of the human brain. Image Credit: sfam_photo / Shutterstock
The researchers explained that there are several brainwave forms, especially slow brain waves, that appear during sleep and were recorded using the EEG (electroencephalogram). The authors wrote: “Sleep is essential for cognition and the maintenance of healthy brain function. Slow waves in neural activity contribute to memory consolidation, while cerebrospinal fluid (CSF) clears metabolic waste from the brain. It is not known whether these two processes are related. ”
The new study reveals that before each of these slow waves occurs in the sleeping brain, there is a CSF pulse that washes the entire brain to remove toxins from it. This means that approximately every 20 seconds or so, the brain is flushed. CSF is usually the fluid that flows around the brain and spinal cord.
Laura Lewis, lead author of the study and assistant professor in the University of Boston's Department of Biomedical Engineering, said this study reveals the link between sleep deprivation and neurodegenerative disorders such as Alzheimer's disease. She said, "Some disturbances in the way sleep is working could potentially be contributing to the decline in brain health."
The researchers believe these findings point to the fact that individuals can reduce their risk of getting Alzheimer's disease by getting good quality sleep each night. Experts said people with Alzheimer's tend to sleep poorly. Now this study links the two conditions. Lewis said: "It has long been known that sleep is really important for brain health … but why is it more mysterious."
To study the effect of sleep on the brain, the team used functional magnetic resonance imaging or magnetic resonance imaging to study the brains of 13 sleeping participants. They wrote that they used "accelerated neuroimaging to measure physiological and neural dynamics in the human brain." They analyzed a number of parameters, including brainwaves and CSF flow. Lewis explained, "And that's when we discovered that during sleep there are very large, slow waves that occur perhaps once every 20 seconds of CSF flushing in the brain." She added that it was like a big slow washing machine that got in pulses.
Lewis said another important finding from this study was that before the CSF washed the brain, there was a brainwave – an electrical wave that covered the entire brain. She said: “Before each wave of fluid, we would see a wave of electrical activity in the neurons. This electric wave always happens first, and the CSF wave always follows seconds later. "
They noted that it was the electric wave that triggered the flow of the CSF. The wave was the slow brain wave that is seen in the NREM (rapid eye movement) sleep stage or deep stage. The authors wrote: "During non-rapid eye movement sleep, low frequency oscillations in neural activity support memory consolidation and neuronal calculus."
Lewis added: "People with Alzheimer's disease are known to have fewer of these electrophysiological slow waves and thus have fewer and fewer slow waves." Now it is known that less of these waves also means less washing of toxins. Lewis explained: "It would make sense that if there are large waves of liquid from the CSF, this in turn can cause mixing and dispersion with other brain fluids and help with this waste removal process."
Another finding from MRI scans revealed that CSF flow increased with decreasing blood flow. They noted that lower blood flow allowed CSF to better cleanse the brain and would better allow toxin removal. The team wrote: "Slow oscillatory neuronal activity leads to oscillations in blood volume, drawing cerebrospinal fluid into and out of the brain."
The authors concluded: "These results demonstrate that the sleeping brain exhibits CSF flow waves on a macroscopic scale and this CSF dynamics is interconnected with neural and hemodynamic rhythms." Lewis says this study may be the beginning of understanding how declining brain toxin removal may be contributing to Alzheimer's disease and other diseases and how sleep waves and CSF flow can help. This, in turn, may also mean that therapeutic treatment of neurodegenerative disorders may focus on this aspect of developing conditions, the team explained.
Electrophysiological, hemodynamic and cerebrospinal fluid oscillations coupled in human sleep, Nina E.Fultz, Giorgio Bonmassar, Kawin Setsompop, Robert A. Stickgold, Bruce R. Rosen, Jonathan R. Polimeni, Laura D. Lewis, Science 01 Nov 2019: Vol . 366, Issue 6465, pp. 628-631, DOI: 10.1126 / science.aax5440, https://science.sciencemag.org/content/366/6465/628