The word mitochondria may conjure a faint memory from a high school biology class, accompanied by the phrase "powerhouse of the cell." That description is technically accurate, but it captures almost nothing of what these structures actually do or how profoundly they shape every dimension of how you feel, function, and age.

For decades, the study of sleep focused primarily on what the brain does during rest: how memories consolidate, how hormones regulate, how the body repairs muscle tissue, how emotional processing occurs overnight. What scientists did not fully understand was what the brain does to maintain itself, to quite literally clean up after the demands of a full day of activity. That understanding arrived in 2013, when a team of researchers led by neuroscientist Maiken Nedergaard at the University of Rochester made a discovery that would change the way science thinks about sleep and brain health.