Deep sleep5/29/2023 ![]() ![]() What the team found was that the slow waves seen in non-REM sleep occur in lockstep with changes in both blood flow and CSF. ![]() “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.” “We realized we could take advantage of this to measure CSF flow at the same time as blood oxygenation,” Lewis says. The latter was only possible due to a flaw in this method that means any newly arriving fluid (not just oxygenated blood) lights up in the image. That allowed for the measurement of both blood-oxygenation changes (which indicate blood flowing to electrically active, oxygen-hungry regions) and CSF flows. The researchers used electroencephalography (EEG) to monitor the brain waves of 13 sleeping healthy adults, while also using a cutting-edge, “accelerated” fMRI technique to capture faster changes than standard fMRI can manage. “That led us to ask what was happening in the CSF.” “We know sleep is really important for brain health, and waste clearance is probably a key reason why what was less clear is: Why is this changed during sleep?” Lewis says. In the study, published on October 31 in Science, the team set out to investigate how the dynamics of CSF flow changes during sleep, and how this might relate to alterations in brain blood flow and electrical activity. “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.” “We’ve discovered there are really large waves of CSF that appear in the brain only during sleep,” Lewis says. The work has implications for understanding the relations between sleep disturbance and psychiatric and neurodegenerative conditions, and may even point to new approaches to diagnosis and treatment. A new study, from a team led by neuroscientist Laura Lewis of Boston University, now gives insight into what drives CSF flow through the brain, suggesting that the same slow waves that coordinate memory consolidation drive oscillations in blood flow and CSF in the brain. ![]() One aspect of sleep that is well understood is how the slow electrical oscillations (or “slow waves”) that characterize deep, non-REM sleep contribute to memory consolidation, the process whereby new memories are transferred into long-term storage. Researchers think cerebrospinal fluid (CSF) may flush toxic waste out, “cleaning” the brain and studies have shown that garbage clearance is hugely improved during sleep. They were not sure exactly how all this works, however, or why it should be so enhanced during sleep. Why sleep has restorative-or damaging-effects on cognition and brain health has been an enduring mystery in biology. ![]()
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