The scientists discovered that during sleep a ‘plumbing system’ called the glymphatic system may open, letting fluid flow rapidly through the brain.
The glymphatic system helps control the flow of cerebrospinal fluid (CSF), a clear liquid surrounding the brain and spinal cord.
The flush of this fluid into the brain also helps to clear away toxins, some of which are associated with Alzheimer’s disease and other neurological disorders.
To aid this flushing out, the scientists found that, when we are asleep, the space between our brain cells expands dramatically.
For example, in the mice in this study, the space inside the brains increased by 60% when the mice were asleep or anesthetised.
All this activity is very energy intensive, however, and the scientists speculate that the brain has to make a choice about how best to manage the many demands made on it on a daily basis.
According to Dr Nedergaard, “The brain only has limited energy at its disposal and it appears that it must choice between two different functional states – awake and aware or asleep and cleaning up.
“You can think of it like having a house party. You can either entertain the guests or clean up the house, but you can’t really do both at the same time.”