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| Sleep Does Not Aid in Brain Toxin Clearance, Study Suggests |
Professor Nick Franks, a biophysics and anesthesia expert at Imperial College London and co-lead of the study, commented, "It sounded like a Nobel prize-winning idea. If you are sleep-deprived, countless things go wrong – you don't remember things clearly, hand-eye coordination is poor. The idea that your brain is doing this basic housekeeping during sleep just seems to make sense."
The restorative effects of a good night's sleep are widely recognized, and the prevailing scientific explanation has been that the brain eliminates toxins during sleep.
However, recent findings challenge this theory, which has become a dominant view in neuroscience. The study discovered that the clearance and movement of fluid in the brains of mice were actually reduced during sleep and anesthesia.
Professor Nick Franks, a biophysics and anesthesia expert at Imperial College London and co-lead of the study, commented, "It sounded like a Nobel prize-winning idea. If you are sleep-deprived, countless things go wrong – you don't remember things clearly, hand-eye coordination is poor. The idea that your brain is doing this basic housekeeping during sleep just seems to make sense."
Yet, there was only indirect evidence that the brain's waste-removal system becomes more active during sleep, according to Franks.
In the latest study, published in the journal Nature Neuroscience, researchers used a fluorescent dye to examine the brains of mice. This allowed them to observe how quickly the dye moved from fluid-filled cavities (ventricles) to other brain regions and directly measure the rate of dye clearance from the brain.
The study revealed that the clearance of the dye was reduced by about 30% in sleeping mice and 50% in mice under anesthesia, compared to mice that remained awake.
Franks noted, "The field has been so focused on the clearance idea as one of the key reasons why we sleep, and we were, of course, very surprised to observe the opposite in our results. We found that the rate of dye clearance from the brain was significantly reduced in animals that were asleep or under anesthesia."
The researchers anticipate that these findings will apply to humans since sleep is a fundamental need shared by all mammals.
Professor Bill Wisden, interim director of the UK Dementia Research Institute at Imperial College London and co-lead author, emphasized, "While there are many theories about why we sleep, and although we've shown that clearing toxins may not be a primary reason, it cannot be disputed that sleep is important."
These findings hold relevance for dementia research due to the growing evidence of a link between poor sleep and Alzheimer's risk. It remains unclear whether lack of sleep directly causes Alzheimer's or if it is merely an early symptom. Some had hypothesized that insufficient sleep might hinder the brain's ability to clear toxins effectively, but the latest research casts doubt on the plausibility of this explanation.
Franks added, "Because that idea has held such sway, it's probably increased people's anxiety that if they don't sleep, they'll be more likely to develop dementia."
Wisden concluded, "The other aspect of our study is that we've demonstrated that brain clearance is highly efficient during the waking state. In general, being awake, active, and exercising may more effectively cleanse the brain of toxins."
