Every night we all participate in a small biological miracle—the transition from wakefulness to sleep. Last September researchers at Washington State University made a notable advance in understanding the chemical trigger that allows that shift to happen.
The key to sleep turns out to be one of the body’s most important molecules: ATP, the compound that stores energy for use in metabolism. Neurobiologist James Krueger and his colleagues discovered that repeated firing of neurons in the brain while we are awake causes them to release ATP into the spaces between the cells. As the molecule accumulates, it bonds to neighboring neurons and glial (support) cells; this allows the cells to absorb other chemicals—such as tumor necrosis factor and interleukin 1—that most likely put those cells into a sleep state.
This finding implies that sleep “is not a whole brain phenomenon,” Krueger says. It occurs only in neural circuits that have been most active during the day and so have released the most ATP. Translation: Some parts of the brain can remain relatively alert even after we fall asleep. “This is an extremely important finding,” says Mark Mahowald, a sleep expert at the University of Minnesota who was not involved in the research. “The notion that only part of the brain sleeps fits very well with our understanding of sleepwalking, when individuals have their eyes open and easily navigate around objects yet have no conscious awareness of doing this.” A clearer picture of ATP’s role in the process could point the way to new drugs for treating insomnia and other sleep disorders.