When we sleep, our brains flush out waste that builds up during our waking hours, but how this happens has been something of a mystery. A new study of sleeping mice has visualized and tracked the flow for the first time. The researchers found that, during a specific sleep phase (the non-rapid eye movement portion), the mice released pulses of norepinephrine — a cousin to adrenaline — that periodically contracted blood vessels in the rodents’ brains. As these blood vessels contract and relax, it forces the nearby cerebrospinal fluid to flow. In short, the pulsing of the blood vessels pumps the fluid bathing the brain, flushing it.
The team also found that certain medications — like the sleep aid Ambien — disrupted this flow in mice by suppressing the blood vessels’ oscillations. It’s not known yet whether our brains operate on the same pumping principle or whether medications could affect that, but it does suggest that a similar study in humans is worthwhile. (Image credit: K. Howard; research credit: N. Hauglund et al.; via Science)