The brainwashing cycle

While we sleep, aneurological deep clean takes place that is crucial for filtering out toxins and warding off dementia. Here's how to optimise it

- By Linda Geddes

Tonight, and almost every night, something amazing will happen inside your brain. As you turn off the light switch and fall asleep, you will be switching on the neurological equivalent of a dishwasher deep-clean cycle. First, the activity of billions of brain cells will begin to synchronise, and oscillate between bursts of excitation and rest. Coupled with these "slow waves", blood will begin to flow in and out of your brain, allowing pulses of the straw-coloured cerebrospinal fluid (CSF) that usually surrounds your brain to wash in and be pushed through the brain tissue, carrying the day's molecular detritus away as it leaves.

Most people recognise that if they don't get enough sleep, their mood and memory will suffer the next day. But mounting evidence is implicating this "brainwashing" function of sleep in longer-term brain health.

"Sleep is not just a state where things turn off. Sleep is a very active state for the brain - and it seems to be a special state for fluid flow within the brain," said Laura Lewis, assistant professor of biomedical engineering at Boston University in the US, who has captured images of this pumping process in sleeping humans.

If we don't get enough regular sleep, these toxic byproducts can accumulate, gradually increasing our risk of dementia and brain diseases. We tend to get less deep sleep as we get older, making it harder to clear out the debris. Fortunately, scientists are homing in on ways to boost this kind of sleep, which could ultimately help to keep our brains healthier for longer.

It wasn't until 2012 that Prof Maiken Nedergaard at the University of Rochester Medical Center in the US and her colleagues identified a plumbing system in the brain that springs to life during sleep, and enables the organ to clean itself.