For grownups, drifting off for an afternoon snooze is often easier said than done. But many of us have probably experienced just how simple it can be to catch those zzz's in a gently rocking hammock.
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WASHINGTON: The rocking motion of a hammock improves sleep quality and helps people get to sleep faster, according to a team of Swiss and French scientists.
A new study looked at 12 male volunteers who were not habitual nappers but who agreed to try an afternoon snooze on both a stationary bed and a rocking bed while machines scanned their brains, eye and muscle movements.
The results suggest that napping on a slowly swinging bed really does get us to sleep faster. To the researchers' surprise, rocking also changes the nature of our slumber, encouraging deeper sleep.
"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," said Sophie Schwartz of the University of Geneva in Switzerland.
"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."
Boosting sleep
For an experiment reported in Current Biology, the researchers asked 12 adult volunteers to nap on a custom-made bed or 'experimental hammock' that could either remain stationary or rock gently.
All participants were good sleepers who didn't typically nap and did not suffer from excessive sleepiness during the day. Each participant took two 45-minute afternoon naps, one with the bed stationary and one with the bed in motion, while their brain activity was monitored by electroencephalogram (EEG).
"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," said Michel Muhlethaler of the University of Geneva. "Surprisingly, we also observed a dramatic boosting of certain types of sleep-related [brain wave] oscillations."
Falling asleep faster
More specifically, rocking increased the duration of stage N2 sleep, a form of non-rapid eye movement sleep that normally occupies about half of a good night's sleep.
The rocking bed also had a lasting effect on brain activity, increasing slow oscillations and bursts of activity known as sleep spindles. Those effects are consistent with a more synchronised neural activity characteristic of deeper sleep.
Two of the 12 men had to be left out of the final analysis because one had a malfunctioning EEG and one experienced too much anxiety to fall asleep on the day he was assigned to the stationary bed. Women were excluded from the study because the menstrual cycle can have an effect on electroencephalogram (EEG) monitoring, the researchers said.
Treatment for insomnia?
Schwartz and Mühlethaler say the next step is to find out whether rocking can improve longer periods of sleep and to find out whether it may be useful for the treatment of sleep disorders, such as insomnia.
Also, they added, 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.
