June 21, 2011

Hammocks Are Best For Afternoon Naps

Napping on a slowly swinging bed helps us to both fall asleep faster and encourages a deeper sleep than stationary beds, according to findings published in the June 21 issue of Current Biology, a Cell Press publication.

"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," says one of the study's co-authors, Sophie Schwartz of the University of Geneva.

"The goal of our study was twofold," she says," to test whether rocking does indeed soothe sleep, and to understand how this might work at the brain level."

Twelve participants, who were not habitual nappers and did not suffer from excessive sleepiness, were recruited for the study.  Each person was asked to take two 45-minute afternoon naps on a custom-made bed or "experimental hammock" that either remained stationary or was made to gently rock.

During these naps, each participant had their brain, eye and muscle movements scanned by electroencephalogram (EEG).

All twelve participants were men, since women's menstrual cycle can have an effect on EEG monitoring, researchers say.

Two of the twelve men were left out of the final analysis because AFP reports that one had a malfunctioning EEF and the other experienced too much stress to fall asleep on his assigned day for the stationary bed.

However, from the small sample of participants, researchers found that all fell asleep faster in the rocking bed than in the still one. In addition, their 45-minute nap was deeper.

"We observed a faster transition to sleep in each and every subject in the swinging condition, a result that supports the intuitive notion of facilitation of sleep associated with this procedure," says Michel Mhlethaler of the University of Geneva and fellow co-author.

"Surprisingly we also observed a dramatic boosting of certain types of sleep-related oscillations."

Rocking increases the duration of stage N2 sleep, which is a form of non-rapid eye movement sleep that normally occupies about half of a good night's sleep.

Furthermore, "the rocking bed had a lasting effect on brain activity, increasing slow oscillations and bursts of activity known as sleep spindles," which are effects that are consistent with a more synchronized neural activity characteristic of deeper sleep.

Future research is needed to find out whether rocking can improve longer periods of sleep, and possibly be useful for the treatment of sleeping disorders such as insomnia, says the study.

In addition, researchers added that "because sleep spindles have been associated with brain plasticity mechanisms, enhancing spindle activity with rocking may be good for memory consolidation and may have the potential to improve brain repair mechanisms after brain damage."


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