May 14, 2024 23:00:00

It is pointed out that the brain's ability to flush out waste products is weakened during sleep and anesthesia

In March 2024, researchers from the University of Washington published a paper claiming that

they had elucidated the mechanism by which sleep flushes waste products from the brain . However, a team of researchers from Imperial College London has made the exact opposite point, that the ability to flush waste products is actually weakened during sleep.

Brain clearance is reduced during sleep and anesthesia | Nature Neuroscience
https://www.nature.com/articles/s41593-024-01638-y

Sleep doesn't help brain wash out toxins, study suggests | Neuroscience | The Guardian

https://www.theguardian.com/science/article/2024/may/13/sleep-does-not-help-brain-wash-out-toxins-study-suggests

A previous study by Jonathan Kipnis and others at the University of Washington analyzed the brains of mice and showed that rhythmic brain waves are generated during sleep, and that they flush waste products by sending cerebrospinal fluid to brain tissue. It has been confirmed that if rhythmic brain waves are inhibited, fresh cerebrospinal fluid is not sent and waste products remain.

Mechanism by which sleep flushes waste from the brain is elucidated, which may help prevent neurodegenerative diseases such as Alzheimer's - GIGAZINE

Andawei Miao and Nicholas P. Franks of Imperial College London also looked at mouse brains.

'Sleep deprivation causes a whole host of problems, so it seems logical that the brain might do some kind of 'housekeeping' while we sleep,' Franks acknowledges. 'But there is only indirect evidence that the brain's waste-cleaning systems are more active during sleep.'

Miao and his colleagues added a fluorescent dye to the cerebrospinal fluid filling the ventricles , allowing them to see how the fluid moved through the brain.

The results showed that cerebrospinal fluid movement was reduced by 30% during sleep and 50% during anesthesia compared to when the subjects were awake.

Because sleep is a need common to all mammals, the researchers believe this finding could have implications for humans as well.

Professor Bill Wisden, interim director of the UK Dementia Institute at Imperial College London, said of the findings: 'There are many theories about why we sleep, but what this shows is that at least eliminating waste products is not the main reason. But there's no denying that sleep is important.'

Although there has been an increasing number of studies linking sleep deprivation to the risk of Alzheimer's disease in recent years, it remains unclear whether sleep deprivation causes Alzheimer's disease or whether sleep deprivation is an early symptom of Alzheimer's disease.

One hypothesis has been that if you don't get enough sleep, your brain doesn't flush toxins as effectively, but this study casts doubt on the validity of this hypothesis.

Professor Wisden said: 'Sleep problems are a common symptom in people with dementia, but it is not yet known whether they are a consequence of the progression of the disease or a cause of it. Getting good sleep may help to reduce the risk of dementia for reasons other than flushing toxins.'

Another aspect of this study is that it shows that the brain's ability to clear waste products is more efficient when you're awake. 'It may be that people who are active are more effective at clearing toxins from their brains,' says Professor Wisden.