A new study in mice might help to explain why it's so hard to drift off to dreamland when you're engrossed in a page-turning book.
Researchers from the University of Texas Southwestern Medical Center found that mice that were kept awake by appealing to their curious natures had a harder time falling asleep than mice that were just gently kept awake -- even when both groups of mice were sleep-deprived.
"This study supports the idea that subjective sleepiness is influenced by the quality of experiences right before bedtime. Are you reluctantly awake or excited to be awake?" study researcher Dr. Masashi Yanagisawa, a professor of molecular genetics and a Howard Hughes Medical Institute investigator at the university, said in a statement.
For the study, published in the journal Proceedings of the National Academy of Sciences, researchers took mice that were virtually identical genetically and split them up into three groups. The first group of mice were allowed to sleep and be awake with no interruption by researchers. But the second and third groups of mice had sleep delayed by six hours.
Researchers kept the second group of mice awake by appealing to their sense of curiosity -- they changed their cages so that they would spend time exploring the new changes (which researchers likened to kids staying up late to play a brand-new video game). The third group, meanwhile, was kept awake just gently -- by tapping on the cage lightly when the mice looked like they were drifting off, for instance (similar to a parent who has to stay awake to wait for their child to come home from a late night outing).
They found that even though both the second and third groups of mice had delayed sleep and therefore the same kind of need for sleep, the ones that were gently kept awake drifted off to sleep faster than the mice that were kept awake because they wanted to explore.
Plus, researchers identified two new proteins that seemed to play a role in these sleep responses.
"Two of the great mysteries in neuroscience are 'Why do we sleep' and 'What is sleep's function?'" study researcher Dr. Robert Greene, a psychiatry professor at the university and a doctor at the Dallas VA Medical Center, said in a statement. "Separating sleep need from wakefulness and identifying two different proteins involved in these steps represents a fundamental advance."