We know babies benefit from being rocked to sleep - now a study suggests it helps adults sleep better too.
Researchers from the University of Geneva built a special bed that rocked gently throughout the night.
They tested it on 18 young adults and found they woke up fewer times and slept more deeply than on a normal bed.
Scientists said the rocking motion resulted in a longer period of slow brainwaves which caused deep sleep, and improved their memory.
The volunteers spent three nights at a sleep laboratory in Geneva: one to get them used to sleeping there, one on a rocking bed and the other on the same bed, but in a still position.
Electrodes recorded their brainwaves, and found that the period of deep sleep was extended by rocking.
Laurence Bayer, lead study author and researcher at UNIGE Faculty of Medicine, pointed out that the rocking motion was slow enough not to cause nausea.
"A hammock would probably not be as efficient, although people often report a sense of relaxation when rocked in a hammock," she said.
"In our paper we test the effect of rocking on one night, but we have no idea if the effects will still be there over a long-term period."
The researchers also found the adults had better memory recall in the morning if they slept on the rocking bed.
Aurore Perrault, another researcher at the faculty, said: "To see if this also affected memory, we subjected our participants to memory tests: they had to learn pairs of random words in the evening and remember them in the morning when they woke up," she said.
"Here too, rocking proved beneficial: the test results were much better after a night in motion than after a still night."