June 21, 2011 -- The gentle rocking motion of a hammock helps people fall asleep faster and encourages a deeper state of sleep than sleeping on a stationary bed, a new study shows.
"It is a common belief that rocking induces sleep: We irresistibly fall asleep in a rocking chair and, since immemorial times, we cradle our babies to sleep," researcher Sophie Schwartz of the University of Geneva in Switzerland says in a news release.
"Yet, how this works had remained a mystery. The goal of our study was twofold: to test whether rocking does indeed soothe sleep, and to understand how this might work at the brain level," Schwartz says.
How Hammocks Help Sleep
In the study, 12 healthy adults napped in a custom-made bed that could rock gently like a hammock or remain stationary. Each participant took one 45-minute afternoon nap while the bed was stationary and another nap while it was in motion.
During each nap, researchers monitored brain activity using an electroencephalogram (EEG).
Researchers found that not only did participants fall asleep faster in the hammock-like bed, but the gentle rocking motion also changed the nature of their sleep.
"We observed a faster transition to sleep in each and every subject in the swinging condition," researcher Michel Mühlethaler, also from the University of Geneva, says in the release. "Surprisingly, we also observed a dramatic boosting of certain types of sleep-related [brain wave] oscillations."
The results, published in Cell Biology, showed the rocking bed increased slow oscillations and bursts of activity in the brain known as sleep spindles, which are associated with deep sleep and memory consolidation.
Researchers also found the rocking motion increased the duration of stage N2 sleep, a type of non-rapid eye movement sleep that usually takes up about half of a good night’s sleep.
In addition, eight of the participants rated the rocking hammock-like bed as “more pleasant” than the stationary bed.
Researchers say the results suggest that rocking to soothe and induce sleep is an adaptive human behavior that has evolved over the years to encourage the natural oscillations that occur in the brain during sleep.
They say the next step is to find out whether harnessing the sleep-inducing power of the hammock may be used to treat sleep disorders, such as insomnia.