Study: The brain cleans itself more slowly in people who are starting to become forgetful
The brain’s own cleaning system appears to function less effectively in people who have memory problems. Researchers are now investigating whether sleep could help explain why.
Brain researchers from the University of Oslo are trying to find out what brain ''washing' means for our brain health. The brain needs to be cleared of proteins.(Stock photo: DimaBerlin / Shutterstock / NTB)
For a long time, this fluid was mainly thought to serve as protection for the brain. But in recent years, researchers have discovered that it may also play an important role in transporting waste products.
When researchers add a tracer to the brain fluid, they can see that it moves along the outside of blood vessels and throughout the brain before eventually being flushed out.
Tracked a substance through the brain
There is now increasing research into what this ‘brain cleansing’ process could mean for our brain health.
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Researchers hope that these findings could eventually contribute to the treatment of brain conditions such as Alzheimer’s disease.
In a new pilot study carried out at the Memory Clinic at Oslo University Hospital, researchers examined 27 people with mild cognitive impairment. They took part in the working-memory training study REACT MCI (link in Norwegian).
All of them had begun experiencing memory problems, but none had developed dementia.
The participants received a tracer in the fluid surrounding the brain and spinal cord. Researchers then collected blood samples to determine how quickly the substance was removed.
Their results were compared with those of healthy individuals.
Found a clear difference
In the study, which has not yet been published, the researchers saw a clear difference between the two groups in how effectively the brain cleared the tracer. The research team is based at the K.G. Jebsen Centre for Brain Fluid Research at the University of Oslo.
In people with memory problems, the cleansing process was much slower than in the healthy participants.
"It took two and a half times as long for the tracer to be cleared in those who had mild cognitive impairment," one of the researchers behind the study, Professor Anne-Brita Knapskog, said at a public event earlier this month.
Memory researchers from the K.G. Jebsen Centre for Brain Fluid Research at a public event in Arendal. From left: Moderator Anne-Rita Øksengaard from the Norwegian Health Association, Per Kristian Eide, Rune Enger, Anne-Brita Knapskog, and Susanne Hernes.(Photo: Siw Ellen Jakobsen)
Is it related to sleep?
Researchers do not yet know why this happens.
However, previous research suggests that one factor may influence how brain fluid moves through the brain: sleep.
This is difficult to study in humans. For that reason, the same research group at the K.G. Jebsen Centre for Brain Fluid Research previously studied the brains of sleeping mice. They surgically implanted a window into the mice's brains, allowing them to observe what happens during completely natural sleep.
The researchers believe that the blood vessels in the brain play a special role.
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“Using tiny microscopes, we can follow the blood vessels in the brains of sleeping mice,” says Professor Rune Enger, who took part in the mouse study.
Helping to clean the brains of mice
When the mice are awake, the blood vessels contract slightly and then expand again. But when they sleep, these movements become stronger and more rhythmic.
The researchers believe that these movements may function as a kind of pump. As the blood vessels expand and contract, they may help pus the brain fluid through the brain.
“If brain fluid helps carry waste substances out of the brain, this could be one explanation for why sleep is so important for the brain’s ‘cleaning’ process,” says Enger.
Research suggests that something similar happens in humans.
The research group at the K.G. Jebsen Centre for Brain Fluid Research has previously investigated whether sleep also affects the brain’s cleaning system in humans.
In one study, they compared people with good and poor sleep quality.
They found a difference.
People who had poor sleep quality over time showed poorer clearance of the tracer substance than those who slept well.
“This may suggest that sleep affects our ability to clear waste from the brain,” says Per Kristian Eide. He is also a professor at the K.G. Jebsen Centre for Brain Fluid Research.
What does this mean for Alzheimer’s?
In Alzheimer’s disease, certain proteins accumulate abnormally in the brain, particularly beta-amyloid and tau.
Researchers are now interested in investigating whether the brain’s cleansing system influences how effectively these substances are removed.
If the brain becomes less effecient at clearing them away, it is possible that they may accumulate more easily.
Anne-Brita Knapskog says that they have now started a new study of Alzheimer’s patients at the Memory Clinic at Oslo University Hospital.
Can the clearance system be influenced?
When doctors assess whether someone may have dementia, they currently use methods including MRI scans of the brain and tests of cerebrospinal fluid.
The cerebrospinal fluid can be examined for proteins associated with Alzheimer’s disease. MRI scans can also reveal changes in specific areas of the brain.
But the researchers also want to find out how the brain’s cleansing system actually works.
They do this by adding a tracer to the brain fluid and measuring how quickly the substance is transported away. If this process is slow, it may be a sign that the brain is less effective at removing substances.
Can it be influenced?
"In the longer term, we hope to find out whether such measurements can tell us something about the risk of developing dementia," says Susanne Hernes.
She leads the REACT MCI study at the University of Oslo.
"If the cleansing system turns out to play a role in the development of Alzheimer’s disease, the next question will be whether it's possible to influence it. For now, we don't know," she says.
