People have been rocking babies to sleep for thousands of years, and, despite the indignities of getting in and out of them, everybody loves a hammock – so how have we only just discovered that the key to a good night’s sleep as adults is to be rocked gently rather than count sheep?

And yet, that’s just what researchers at the University of Geneva found in a new study published in Current Biology. Not only does rocking help you get some seriously good Zzzzzs, but it also boosts your memory.

Testing their theory on 18 young adults at a sleep facility in Switzerland, the researchers found that continuous whole-night rocking (we’re talking a gentle sway here, not earthquake) has many benefits: the participants fell asleep faster, slept more soundly with fewer interruptions, and had longer periods of deep sleep – when the brainwaves slow and consolidate memory.

“A good night’s sleep means falling asleep quickly and staying asleep all night,” said study lead Laurence Bayer in a statement. “However, we observed that our participants, although they slept well in both cases, fell asleep more quickly when they were rocked. In addition, they had longer periods of deep sleep and fewer micro-wakes, a factor frequently associated with poor sleep quality.”

In a previous study, the team had found that rocking helped people fall asleep faster and more soundly when having a quick 45-minute nap. To test if it was beneficial at night too, they monitored the participants for three nights. The first night allowed them to get used to the facility, the second and third nights were to compare being rocked to sleep on a specially designed moving bed, and sleeping in a boring conventional non-moving one.

^{© Laurence Bayer UNIGE/HUG and Aurore Perrault}

The beds were suspended by the corners in a slightly utilitarian-looking four-poster frame that pushed the mattress 10 centimeters (4 inches) to the side and back every four seconds.

All participants reported the rocking night’s sleep as relaxing and pleasant, but it was the prolonged deep sleep period that allowed the synchronization of neural activity in the thalamocortical networks of the brain, which play an important part in the consolidation of memories.

“To see if this effect also affected memory, we subjected our participants to memory tests: they had to learn pairs of words in the evening and remember them in the morning when they woke up,” explained first author Aurore Perrault. “And here too, rocking proved beneficial: the test results were much better after a night in motion than after a still night! ”

In a super cute second study, the team found that rocking mice to sleep also led them to fall asleep faster and for longer, though it didn't increase sleep quality. This study focused on the vestibular system, in the inner ear, which manages balance and spatial orientation, and which scientists have long suspected is key to sleep. Intriguingly, mice that lacked the part of the vestibular system that senses linear acceleration experienced no benefits to being rocked to sleep, which they say confirms its involvement.