As any parent knows, rocking a baby often helps the child fall asleep.
But would adults reap a similar benefit from being rocked to sleep?
Yes, according to a small but intriguing study published last week in the journal Current Biology. The study found that sleeping in a gently swaying bed affects adult brain activity in a way that promotes deep sleep.
The rocking motion also appears to help consolidate and strengthen memory.
“Having a good night’s sleep means falling asleep rapidly and then staying asleep during the whole night,” says Laurence Bayer, the study’s senior author and a neuroscientist at the University of Geneva, Switzerland, in a released statement. “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.”
To function mentally and physically at our best, we need to get a good night’s sleep. Yet we are chronically sleep-deprived. According to a 2016 survey, more than a third of American adults — 34.8 percent — sleep for less than the minimum recommended seven hours on most nights.
Minnesotans tend to get more sleep than people living in other states. In that same survey, 29.2 percent of Minnesotans said they got less than seven hours of shut-eye on a typical night.
Insufficient sleep has been linked to an increased risk of obesity and many other negative health outcomes, including high blood pressure, heart disease, type 2 diabetes and depression. It also increases the risk of injuries from accidents and mental errors, on and off the job.
Improving people’s sleep experiences has therefore become an urgent public health quest. A few years ago, Bayer and her colleagues demonstrated that a gently rocking bed helped people slept more soundly during a 45-minute nap.
They wanted to see if something similar would happen during nighttime sleep.
How the study was done
For the current study, the researchers recruited 18 healthy Swiss men and women in their early 20s. All were asked to keep a sleep diary and wear a portable actigraph (a device that keeps track of when someone is awake and asleep) at home for three consecutive nights.
The participants then came to a sleep laboratory, where they were hooked up to an electroencephalogram (EEG) machine. It recorded their brain-wave patterns as they slept.
During the first night in the lab, the participants slept in a stationary bed. This night was meant to familiarize them with sleeping in the lab. (Research has shown that we initially have trouble getting a good night’s sleep in a new environment.) On the second night, they slept in either a bed that gently swung from side to side or in an identical stationary bed. (They were randomly assigned to one or the other.)
The participants were also asked to perform tasks that tested their memory before and after each night in the sleep lab.
Days later they returned to the lab and repeated the experiment. This time they slept in the kind of bed (swaying or stationary) that they hadn’t slept in before.
The study found that participants fell asleep about six minutes faster, on average, while being rocked. Furthermore, once asleep, they moved more quickly into non-rapid eye movement (NREM) sleep, and they stayed there longer. NREM — or deep — sleep is the non-dreaming part of the sleep cycle. It’s considered crucial for physical and mental renewal.
When they slept in the rocking bed, the participants also tended to have fewer mini-awakenings during the night. And they scored better on the memory test the next morning.
Further analysis suggested that the continuous rocking reinforced the participants’ deep sleep by modulating their brain wave activity — specifically by synchronizing brain activity in the connective networks between the thalamus and cortex. The thalamus works is believed to work with the cortex to consolidate memory.
In a second study, published in the same issue of Current Biology, researchers at the University of Lausanne in Switzerland found that mice also fell asleep faster and stayed asleep longer when their sleeping quarters — their cages — swayed.
Those experiments pointed to the inner ear, which manages balance and spatial orientation, as playing a role in this finding. Mice without functioning sensory receptors in their inner ear did not benefit from being rocked during sleep, the researchers report.
All of this research comes with caveats, of course. The human study involved only a small group of young, healthy adults. The results might have been different if a larger and more diverse group of people had been brought into the sleep lab.
And the findings from the mice studies, while interesting, may or may not be applicable to humans.
Still, the findings are provocative. The researchers hope that this kind of research will eventually lead to new approaches (rocking beds?) for helping older people with sleep and memory problems, as well as people of all ages with insomnia and mood disorders.
FMI: You can read both studies online in the Feb. 4 issue of Current Biology.