By examining the brain waves in sleeping adults, researchers now have evidence to explain why we find it easier to snooze in a gently rocking hammock.
They found 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 sleep, encouraging deeper sleep.
Sophie Schwartz of the University of Geneva and her colleagues Michel Muhlethaler, Laurence Bayer and Irina Constantinescu 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 Muhlethaler.
"Surprisingly, we also observed a dramatic boosting of certain types of sleep-related [brain wave] oscillations,” he added.
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 synchronized neural activity characteristic of deeper sleep.
The study has been published in Current Biology.