Every night when you sleep, the brain literally washes out toxins built up during the day - but no one's been sure how, until now.
Scientists in the US have discovered a link between slow brain waves during deep sleep and a wave of fluid that washes through, clearing out the mess.
The discovery could pave the way towards new ways to cure or prevent Alzheimer's disease.
"It's been known for a long time that sleep is really important for brain health," study author Laura Lewis told NPR, "but why it is was more mysterious."
Her team put people into MRI machines while they slept measuring their blood oxygen levels, while EEG caps measured the brain's electrical currents.
They found that during deep sleep, the brain's neurons would sync up - turning on and off at the same time. When they were off, the brain doesn't need as much oxygen, so blood flow reduced. In its place, cerebrospinal fluid would wash in.
"Before each wave of fluid, we would actually see a wave of electrical activity in the neurons," Lewis said. "This electrical wave always happens first, and the CSF wave always seems to follow seconds later."
This only happens during deep sleep - not light slumbering or dreaming, and definitely not while people were awake. Previous studies have found a link between not getting enough deep sleep and memory problems.
"It's already known that people with Alzheimer's disease have less of these electrophysiological slow waves, so they have smaller and fewer slow waves," said Lewis.
Alzheimer's has been linked to the build-up of a protein called tau and beta-amyloid. Scientists have struggled to develop drugs that reduce levels of either substance, but this new finding suggests good sleep could be the key.
"It would make sense that if there's large waves of fluid... that that might in turn cause mixing and dispersion with other fluids in the brain and help with this waste removal process," Lewis told NPR.
The findings were published in journal Science on Friday.
Newshub.
