Generations of parents have sung this lullaby to their children: “Rock-a-bye baby on the tree top, when the wind blows the cradle will rock.”
This 18th century nursery rhyme is thought to originate from women working in fields. They placed their baby cradles in trees and let the wind rock them to sleep. A recent study establishes that rocking alters brain activity that benefits sleep and memory in adults.
This study looked at healthy adults who spent multiple nights in a sleep lab, sleeping on a rocking bed some nights and a stationary bed on other nights. This allowed for monitoring and direct comparison of the same subjects under both conditions.
The results from this study were striking. During the nights spent on a rocking bed, subjects fell asleep quicker, they slept more deeply and they slept for longer periods compared to the stationary bed.
Subjects learned word pairs in the evening and were tested on them in the morning. Subjects performed better on the tests after a night sleeping in the rocking bed.
To prove that rocking altered brain activity, researchers used electroencephalography measurements to track which stages of sleep the subjects experienced.
Stage N1 is the transition from being awake to falling asleep. In stage N2, your body responds by slowing your heart rate and breathing. Stage N3, or slow wave sleep, is a regenerative time that allows for body healing and repair. Stage R, or rapid eye movement sleep, is where dreaming episodes occur.
The stages are measured by oscillations in brain networks, which play an important role in sleep and the consolidation of memories. The rocking motion shortened the time it took subjects to reach stage N1, lengthened the N3 stage of sleep and decreased arousals. These results indicate that important alterations stemming from rocking enhanced healthy sleep.
A different study from research groups in Switzerland used a mouse model to show similar positive impacts from rocking, and they have likely identified the cause.
This group focused on the mouse vestibular system, using rocking for rhythmic stimulation. The vestibular system is in the inner ear and it allows us to perceive motion, maintain our balance and sense up and down.
These animal studies indicated that sensory systems involved in the animal’s ability to sense their environment were critical to the benefit obtained from rocking.
Mice that lacked the function in the vestibular system did not benefit from the rocking enhancement of sleep. Mice placed under rocking conditions showed a reduced time to fall asleep and a longer time spent in the N2 stage of sleep. However, the mice didn’t appear to sleep more deeply.
Overall, this study shows that the motion effects on the vestibular system were the source of the beneficial effects of rocking. It would not be surprising if this is the same mechanism in humans.
As someone who struggles to get consistent sleep, I and 40 million other sleep-deprived Americans look forward to additional research and a therapeutic approach to a good night’s sleep.