That fuzzy feeling after pulling a few all-nighters is all in your head.

Really. Scientists say in an April issue of the journal Science, that large amounts of proteins clog up the neural connections in sleep-deprived brains. Proteins at the connection between neurons allow snappy neural communication.

Looking at microscope images of sleep-deprived brains of fruit flies, scientists found that the longer the brain is kept awake, the more protein builds up at the connections. Significantly less protein build-up was seen in brains of well-rested flies.

The researchers think that sleep allows the brain to prepare for effective neural communication of the coming day, by clearing away unnecessary protein that built up during the past day. Similar chemical changes were also seen in rats’ brains during an earlier study, which suggests that sleep allows important maintenance across a diverse range of animals.

So if you don’t want to feel like a zombie tomorrow, we suggest you get some decent shut-eye tonight.