The swinging motion of a rocking hammock reinforces our brain’s natural sleep rhythms in a way that sleeping in a stationary bed does not, said researchers in Switzerland who believe they have discovered the science behind the age-old belief that rocking soothes sleep. Their study, published in Current Biology this week, also suggests that by enhancing the brain’s “spindle activity”, rocking may also help consolidate memory and repair the brain after damage.
We cradle babies to sleep, and we find it hard to stay awake in a gently swaying hammock. These ancient truths cut across cultures and generations, yet the “nature of the link between rocking and sleep is poorly understood”, write Sophie Schwartz of the Department of Neuroscience at the University of Geneva and colleagues, who set out to show that the motion of swinging affects the physiological parameters of human sleep.
Schwartz told the press:
“The goal of our study was twofold: to test whether rocking does indeed soothe sleep, and to understand how this might work at the brain level.”
To that end, they studied the brainwaves of 12 adult volunteers while they took afternoon naps.
They found that napping on an “experimental hammock” comprising a custom-made bed that could be made to rock gently, helped the participants get to sleep faster, but to their surprise, the researchers also found that the rocking motion changed the nature of sleep: it encouraged deeper sleep.
The volunteers were all good sleepers who did not suffer from excessive sleepiness during the day and did not normally take a nap during the day. They each took two 45-minute naps on the custom-made bed: one time with the bed rocking gently and another time with the bed stationary.
While the volunteers were asleep, the researchers monitored their brain activity using polysomnography and electroencephalogram (EEG) spectral analyses.
Co-author Michel Mühlethaler, also from the Department of Neuroscience at the University of Geneva, said each volunteer fell asleep more quickly when the bed was in the hammock mode, reinforcing the intuitive idea that rocking facilitates sleep, and, to their surprise, they also “observed a dramatic boosting of certain types of sleep-related [brain wave] oscillations.”
More specifically, they found that lying on a slowly rocking bed (with a swing frequency of 0.25 Hz) helped the transition from waking to sleep, and increased the duration of N2 sleep, a form of non-rapid eye movement sleep that normally takes up about half of a good night’s sleep.
When asleep on the rocking bed, the volunteers’ brain activity also showed an increase in slow oscillations, and more bursts of an activity known as “sleep spindles”. Both effects indicate the more synchronized brain activity of a deeper and more refreshing sleep.
The researchers concluded that, at the very least, their results “provide scientific support to the traditional belief that rocking can soothe our sleep”.
They now want to investigate the effect of rocking on longer periods of sleep, and whether it can help treat sleep disorders like insomnia.
They suggest that because sleep spindles have been linked with brain plasticity, or the ability of the brain to reorganize its neural pathways, perhaps rocking could be used to enhance memory consolidation and even help improve ways for the brain to repair itself after damage.
Laurence Bayer, Irina Constantinescu, Stephen Perrig, Julie Vienne, Pierre-Paul Vidal, Michel Mühlethaler, Sophie Schwartz.
Current Biology Volume 21, Issue 12, R461-R462, 21 June 2011
DOI:10.1016/j.cub.2011.05.012
Additional source: Cell Press.
Written by: Catharine Paddock, PhD