Two new studies, one of which was conducted in young adults and the other in mice, add to evidence for the benefits of a rocking motion during sleep. In fact, the study in people shows that rocking not only leads to better sleep, but it also boosts memory consolidation during sleep.
“Having a good night’s sleep means falling asleep rapidly and then staying asleep during the whole night,” said Dr. Laurence Bayer, a researcher at the University of Geneva in Switzerland.
“Our volunteers — even if they were all good sleepers — fell asleep more rapidly when rocked and had longer periods of deeper sleep associated with fewer arousals during the night. We thus show that rocking is good for sleep.”
Dr. Bayer and colleagues had earlier shown that continuous rocking during a 45-min nap helped people to fall asleep faster and sleep more soundly.
In the new study, the team wanted to explore the effects of rocking on sleep and its associated brain waves throughout the night.
The researchers enlisted 18 healthy young adults to undergo sleep monitoring in the lab.
The first night was intended to get them used to sleeping there. They then stayed two more nights — one sleeping on a gently rocking bed and the other sleeping on an identical bed that wasn’t moving.
The data showed that participants fell asleep faster while rocking. Once asleep, they also spent more time in non-rapid eye movement sleep, slept more deeply, and woke up less.
Next, the study authors wanted to know how that better sleep influenced memory.
To assess memory consolidation, participants studied word pairs. The researchers then measured their accuracy in recalling those paired words in an evening session compared to the next morning when they woke up.
They found that people did better on the morning test when they were rocked during sleep.
Further experiments showed that rocking affects brain oscillations during sleep.
The rocking motion caused an entrainment of specific brain oscillations of non-rapid eye movement sleep (slow oscillations and spindles). As a result, the continuous rocking motion helped to synchronize neural activity in the thalamo-cortical networks of the brain, which play an important role in both sleep and memory consolidation.
The second study, performed in mice, is the first to explore whether rocking promotes sleep in other species.
And, indeed, it did. A team of researchers headed by University of Lausanne’s Dr. Paul Franken used commercial reciprocating shakers to rock the cages of mice as they slept.
While the best rocking frequency for mice was found to be four times faster than in people, the experiments show that rocking reduced the time it took to fall asleep and increased sleep time in mice as it does in humans. However, the mice did not show evidence of sleeping more deeply.
The authors had suspected that the effects of rocking on sleep were tied to rhythmic stimulation of the vestibular system, the sensory system that contributes to the sense of balance and spatial orientation.
To explore this notion in the mouse, they studied animals whose vestibular systems were disrupted by non-functioning otolithic organs, found in their ears. The experiments showed that mice lacking working otolithic organs experienced none of the beneficial effects of rocking during sleep.
“Taken together, our studies provide new insights into the neurophysiological mechanisms underlying the effects of rocking stimulation on sleep, the researchers said.
“The findings may be relevant for the development of new approaches for treating patients with insomnia and mood disorders, as well as older people, who frequently suffer from poor sleep and memory impairments.”
The results were published in the journal Current Biology.