Researchers in Wisconsin and Italy discovered that when rats were kept awake four hours past their usual bedtime, parts of their brains began to turn themselves off, neuron by neuron, even though the rat was still awake. The shutdown of the neurons was random, but progressive - this was what the researchers thought was responsible for the rats decreasing performance on a task where they had to find a sugar pellet. Researchers said there is no reason to believe this progressive shutdown does not occur in humans.
This finding is important because it means that there could be performance decrements when tired or sleepy, and these decrements could occur before the person even realizes it. There are implications for drivers and those who operate heavy machinery who happen to be sleep-deprived. It could also affect test-taking in sleep-deprived students.