Throughout in example sentence
Our own research, now it's 2,000 years later, suggests that what's happening is that when the brain is awake and is at its most busy, it puts off clearing away the waste from the spaces between its cells until later, and then, when it goes to sleep and doesn't have to be as busy, it shifts into a kind of cleaning mode to clear away the waste from the spaces between its cells, the waste that's accumulated throughout the day.