But we haven't. At least not entirely.
Which is why WSU just got a $1.3 million grant from the National Institutes of Health to study the topic. Sleep scientist Jonathan Wisor will spend the next four years trying to illuminate just one dark corner of the mystery: why the brain's use of glucose plummets while we're sleeping.
From the university:
Glucose is used as an energy source by the body. The brain uses it to fuel its electrical activity, a metabolically demanding process that accounts for as much as 25 percent of the body's glucose use, even though the brain only represents about 5 percent of body mass.
Preliminary data collected by Wisor show that it's the slow-wave phase of sleep—also known as deep sleep—that is responsible for the brain's decrease in glucose metabolism.
"During slow-wave sleep, all of the neurons go through transient periods where they are completely inactive - they're not discharging electrical activity," says Wisor, an assistant professor with the WWAMI medical education program in Spokane who also has research ties with the WSU Sleep and Performance Research Center and the Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology (VCAPP) in the College of Veterinary Medicine. "We're trying to determine what it is about sleep that reduces the demand for glucose relative to the waking brain."
Fascinating stuff, but will it solve the real sleep mystery — why I wake up so hungry when I eat right before going to bed?
Read about another WSU sleep study, in which scientists try to figure out why we make such bad decisions when we're tired.