A new study from the UT Southwestern Medical Center shows the quality of wakefulness affects how quickly a mammal falls asleep. Published in the May issue of Proceedings of the National Academy of Sciences, principal author, Dr. Masashi Yanagisawa, co-author, Dr. Robert Greene, and their team of researchers have identified two proteins linked to alertness and sleep-wake balance.
“Two of the great mysteries in neuroscience are why do we sleep and what is sleep’s function? Separating sleep need from wakefulness and identifying two different proteins involved in these steps represents a fundamental advance,” said Greene, who noted that the study is unique in showing that the need for sleep can be separated from wakefulness both behaviorally and biochemically, meaning the two processes can now be studied individually.
The experiment featured three groups of mice with virtually identical genes. The control group slept and woke at will and followed the usual mouse pattern of sleeping during the day and being awake at night. Treatment of the two test groups was identical and both had the six hours sleep delay, but they were kept awake using different techniques.
The first test group’s sleep was delayed by a series of cage changes. Each cage change was followed by an hour of the mice exploring the new surroundings. This behavior would roughly correspond to teenagers voluntarily delaying bedtime with a new and stimulating event like a rock concert or video game.
Researchers kept the second group awake gently, usually by waving a hand in front of the cage or tapping it lightly whenever the mice appeared to be settling down to sleep. That test group would more resemble parents reluctantly staying awake awaiting a child’s return from a concert.
Both test groups experienced the same amount of sleep deprivation, but were different. In one test, the cage-changing group took longer to fall asleep than the gentle-handling group even though an analysis of their brain waves indicated equal amounts of sleep need in both test groups.
“The need to sleep is as high in the cage-changing group as in the gentle-handling group, but the cage-changers didn’t feel sleepy at all. Their time to fall asleep was nearly the same as the free-sleeping, well-rested control group,” he said.
The researchers identified two proteins that affected these responses, each linked to different aspects of sleep: phosphorylated dynamin 1 levels were linked to how long it took to fall asleep, while phosphorylated N-myc downstream regulated gene 2 protein levels tracked the amount of sleep deprivation and corresponded to the well-known brain-wave measure of sleep need.
“If borne out by further research, this study could lead to new ways of assessing and possibly treating sleep disorders, perhaps by focusing more attention on the hours before bedtime because the quality of wakefulness has a profound effect on sleep,” said Yanagisawa.