Summary: A new study from the UK Dementia Research Institute reveals that sleep may not enhance the brain’s ability to clear toxins, contrary to long-held beliefs. Using a fluorescent dye to track fluid movement in mice brains, researchers found that toxin clearance decreased by 30% during sleep and 50% under anesthesia compared to wakefulness. This challenges the theory that the glymphatic system is more active during sleep. The study, published in Nature Neuroscience, emphasizes the need to explore other reasons why sleep is crucial and how these findings relate to humans.
Key Takeaways:
- The study found that the brain’s ability to clear toxins decreased by 30% during sleep and 50% under anesthesia compared to wakefulness, challenging the idea that sleep enhances toxin removal.
- Researchers used a fluorescent dye to directly measure the rate of toxin clearance in the brains of mice, providing more precise data than previous indirect methods.
- While the study questions the role of sleep in toxin clearance, it underscores the importance of understanding other critical functions of sleep and its impact on conditions like dementia.
The brain’s ability to rid itself of toxins may be reduced during sleep, surprising new UK Dementia Research Institute research reveals.
Over the past decade, a dominant theory as to why we sleep has been that the brain’s ability to clear toxins improves during sleep, or under anesthesia. Until now it’s been thought that sleep clears toxins from the brain via the glymphatic system, a mechanism that flushes waste from the brain. But this has never been conclusively confirmed. Previous studies have used indirect means of measuring the flow of fluid through the brain.
Methodology and Results
In the new study, the researchers used a fluorescent dye to study the brains of mice, seeing how quickly the dye moved from one area of the brain to another and was cleared from the brain. This enabled them to measure the rate of clearance of the dye from the brain directly.
The study showed that the clearance of the dye was reduced by about 30% in sleeping mice and 50% in mice that were under anesthetic, compared with mice that were kept awake.
“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,” says study co-leader Nick Franks, FRS, a professor of biophysics and anesthetics at Imperial College London, in a release. “We found that the rate of clearance of dye from the brain was significantly reduced in animals that were asleep, or under anesthetic. As yet, we do not know what it is about these states that slows down the removal of molecules from the brain. The next step in our research will be to try to understand why this occurs.”
Implications and Future Research
The size of molecules may affect how quickly they move through the brain, and some compounds are cleared through different systems. Therefore, the extent to which the findings are generalizable is not yet confirmed.
The study is published in Nature Neuroscience.
Study co-leader Bill Wisden, PhD, interim center director of the UK Dementia Research Institute at Imperial College London, says in a release, “There are many theories as to why we sleep, and although we have shown that clearing toxins may not be a key reason, it cannot be disputed that sleep is important.
“Disrupted sleep is a common symptom experienced by people living with dementia; however we still do not know if this is a consequence or a driving factor in the disease progression. It may well be that having good sleep does help to reduce dementia risk for reasons other than clearing toxins.
“The other side to our study is that we have shown that brain clearance is highly efficient during the waking state. In general, being awake, active, and exercising may more efficiently clean the brain of toxins.”
Next, the researchers aim to uncover how sleep reduces the clearance of toxins from the brain in mice and explore whether their findings are applicable to humans.
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