You rock! The way to sleep well
Perhaps it's time to swap the bed for a hammock. Samantha Page reports.
Two new studies support the age-old wisdom that being rocked can help people – and mice – fall asleep faster and sleep better. Rocking can even improve memory recall, one study suggests.
Human subjects fall asleep faster, experience more REM sleep, enhance their memory consolidation and sleep more deeply when being rocked, according to research led by Laurence Bayer and Sophie Schwartz of the University of Geneva, Switzerland.
"Having a good night's sleep means falling asleep rapidly and then staying asleep during the whole night," says Bayer. "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."
The researchers looked at EEG readings for 18 young men and women who spent three nights in a sleep study.
The EEG records spindles and slow wave oscillations, and researchers find that these brain waves become synchronised, or “actively entrain,” with the rocking motion.
This may be why overnight memory consolidation was enhanced by sleep rocking. “Sleep oscillations are considered of critical relevance for memory processes,” the researchers note.
Participants in the study performed two cognitive tasks – a vigilance task and a “word-paired associate learning task” – at the beginning and end of each night in the sleep study. The researchers found that while there were no significant changes in the vigilance results, there was “a significant increase in memory improvement during the rocking night”.
A second study, led by Paul Franken of the University of Lausanne, Switzerland, shows that humans are not alone in their sleep-rocking preferences. Mice also fall asleep faster and sleep more soundly, for longer, when they are rocked.
The scientists say this is the first study to show improved sleep with rocking in non-humans.
It’s not entirely clear why humans – or animals – sleep better when they are rocking, but the two research teams, who report their findings concurrently in the journal Current Biology, hypothesise that the effects are at least related to the vestibular system, which is located in the inner ear and helps balance and orientation.
The mouse study found that mice with “non-functioning” otolithic organs did not experience the effects of rocking, supporting the researchers’ hypothesis. (Otolithic organs are key parts of the vestibular system and sense vertical and horizontal movement.)
In other words, if you cannot sense that you are rocking, the rocking does not help lull you to sleep. At least, if you are a mouse.
That is likely true for humans as well. As Bayer, Schwartz and their colleagues write in the human study: “While asleep, we may remain mostly unaware and behaviorally unresponsive to external stimuli. Yet, sensory processing does not cease”.