Ever notice that you sleep like a baby on a hammock? Maybe it's just the slow, soothing rocking motion that reminds grown-ups of being in a parent's arms until their little eyelids finally close.
Inspired by that concept, some Swiss scientists decided to examine the idea of rocking a person to sleep. Researchers wondered whether the see-sawing movement would make adults drift off sooner and how it affected sleep quality.
So they developed an "experimental hammock" -- a custom-made bed that gently swayed from side to side. They asked 12 participants, all of them men ages 22 to 38, who were all good sleepers, to take a 45-minute afternoon nap in this cradle for grown-ups.
They monitored the volunteers' brain waves throughout the nap and compared the results to having these same participants nap in the same bed without any rocking motion. The research appears in the June 21 issue of Current Biology.
"We observed a faster transition to sleep in each and every participant in the swinging condition," says Sophie Schwartz, a neuroscientist at the Sleep and Cognition Neuroimaging Lab at the University of Geneva in Switzerland and the study's lead author.
"Not only does rocking make us fall asleep more quickly, but it also makes people sleep more deeply throughout the nap," she explains.
Compared to nodding off in a stationary bed, those napping in a swinging one had a longer duration of N2 sleep, a type of non-rapid eye movement sleep that makes up about half a night's shuteye. Scientists also observed a dramatic boost in brain-wave patterns seen in deep sleep.
"Motion has specific effects on the brain, and this is precisely what our study shows," says Schwartz. Although researchers expected that rocking would make volunteers conk out sooner, they were surprised it changed the quality of sleep and in such a sustained manner.
Now that they've seen how rocking affects a short nap in healthy adults, the next step is to see how it benefits an entire night's sleep. Other questions they might research include whether the brain changes seen in adults from rocking are also observed in babies, whether motion improves sleep in those with insomnia, and whether it has positive effects on waking performance.
Still there's no need to wait for answers. This summer, put science to the test: Find yourself a hammock or rocking chair in the shade and enjoy that time-honored tradition in some cultures -- the siesta.
