Rocking motion may improve sleep, memory: Study

 Rocking motion during sleep may not only lead to better sleep but also boost your memory, researchers have found. Published in the journal Current Biology, two new studies, one conducted in young adults and the other in mice, add to evidence for the broad benefits of a rocking motion during sleep. One of the studies led by Laurence Bayer and Sophie Schwartz from the University of Geneva in Switzerland, was meant to explore the effects of rocking on sleep and its associated brain waves through the night. 

As many as 18 enlisted healthy young adults were made to undergo sleep monitoring in labs. Assessed over three nights, the subjects had to first get used to sleeping in the labs after which they stayed two more nights -- one sleeping on a gently rocking bed and the other sleeping on an identical bed that was not moving. 

"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," said Bayer. The data also showed that once asleep, the participants spent more time in non-rapid eye movement sleep, slept more deeply, and woke up less. 

To assess memory consolidation, participants studied word pairs and the researchers measured their accuracy in recalling the paired words in an evening session. They then compared those results with the ones drawn from a morning session after the participants woke up. Findings showed, people did better on the morning test after being rocked to sleep the previous night. 

According to researchers, further studies showed that the rocking motion caused an entrainment of specific brain oscillations of non-rapid eye movement sleep. As a result of the entrainment, neural activity in the thalamo-cortical network of the brain, which is an integral part of memory consolidation, was more synchronised. In the second study on mice, led by Paul Franken, of the University of Lausanne in Switzerland commercial reciprocating shakers were used to rock cages of the mice as they slept. 

While the best rocking frequency for mice was found to be four times faster than in people, the findings show that rocking reduced the time it took to fall asleep and increased sleep time in mice similar to the effect on human beings. However, the mice did not show evidence of sleeping more deeply. 

Researchers suspected that the benefits of rocking on sleep were tied to rhythmic stimulation of the vestibular system, that contributes to the sense of balance and spatial orientation. Further study showed that animals whose vestibular systems were blocked by non-functioning otolithic organs (found in their ears), experienced no effect of rocking. 

Taken together, the two studies "provide new insights into the neurophysiological mechanisms underlying the effects of rocking stimulation on sleep," Bayer said. "Current tools, such as optogenetics, can help us decipher which structures receive the stimulus from the otolithic organs and transfer it to structures of the sleep circuitry," Franken said. "Mapping the network of this communication will (help identify)novel clinical targets to cope with sleep disorders, like insomnia and mood disorders," the researchers said.