Scientists have new insight into why we have trouble focusing after a bad night of sleep.

Attention lapses when we’re sleep-deprived result from our brain’s efforts to clean itself up, a process that usually happens during sleep, recent research found. Typically at night, a fluid that surrounds our brain flushes out toxins, cell debris and junk proteins that build up during the day. This cleansing helps curb inflammation and keeps the brain working properly.