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.
