Gentle back and forth … and your eyes get heavy. What is this well-known sleep trick about? Do you actually benefit from the slumber in cradle mode? Researchers have investigated these questions through experimental investigations. You could show: The cradle effect not only makes falling asleep easier, it also benefits the quality of sleep. The sleep optimized by the rocking even leads to an improved memory performance. In a second study on the subject, researchers were also able to show in mice which physical mechanisms the cradle effect is based on.
For some time now, researchers around Laurence Bayer from the University of Geneva have been researching the topic. In a first study, they initially succeeded in scientifically confirming the sleep-inducing effect of the cradle effect: Continuous wobbling as part of a 45-minute nap made a significant contribution to letting subjects fall asleep much faster and deeper. In a further study, they then investigated the extent to which rocking movements also influence the further course of sleep.
For the study, 18 subjects were not only lulled to sleep, but also rocked all night long. They spent two nights in the sleep laboratory – one slept on a gently rocking bed and the other slept on an identical frame that did not move. They were always closely monitored by special devices and the researchers also recorded the brain waves via electrodes on the test subjects’ heads.
Optimized sleep in weighing mode
The results initially confirmed the sleep-inducing effect of the rocking. The data on the further course of sleep then also showed that the proportion of so-called REM sleep, which is characterized by rapid eye movements and characterizes dream sleep, was reduced in weighing mode. Instead, the test subjects spent longer periods in deep sleep and also woke up less frequently, the scientists report. The analysis of the brain waves confirmed these effects. It became apparent that the continuous rocking movement synchronized neuronal processes in the brain, which play an important role for both sleep and memory consolidation.
The researchers tested whether this effect can be demonstrated by giving the test persons memory tasks. You should first memorize pairs of words. They then showed how well they could remember during an evening test and finally after the night in the sleep laboratory. The researchers were able to confirm this: If the test subjects had slept in the cradle mode, they performed comparatively well in the morning test. Bayer comes to the conclusion: “We were able to document that rocking has a positive effect on sleeping and its effects. Our volunteers fell asleep quickly – even though they were all normal sleepers – and then particularly well when they rocked, ”he sums up the result.
Mice can also be lulled to sleep
The second study on the subject dealt with the question of whether the cradle effect is typical for humans or whether it also occurs in other mammals. To investigate this, the research team led by Paul Franken from the University of Lausanne rocked the cages of mice. This showed that even the rodents’ eyes fell very quickly in cradle mode and they slept longer than usual. However, the swing frequency was four times higher than that of humans, the researchers found.
The scientists were then able to use the experimental animals to investigate the mechanism behind the weighing effect. Her suspicions were directed towards the role of stimulating the vestibular system, which is linked to the sense of balance and spatial orientation. To investigate the possible meaning, the researchers carried out experiments with mice in which the function of the vestibular system was disturbed. It turned out that the rocking had no effect on sleep behavior in these animals. It therefore seems clear that the vestibular system plays an important role in the weighing effect.
Current Biology, Perrault et al .: “Whole-Night Continuous Rocking Entrains Spontaneous Neural Oscillations with Benefits for Sleep and Memory” https://www.cell.com/current-biology/fulltext/S0960-9822(18)31662-2 DOI: 10.1016 / j.cub.2018.12.028
Current Biology, Kompotis et al .: “Rocking Promotes Sleep in Mice through Rhythmic Stimulation of the Vestibular System” https://www.cell.com/current-biology/fulltext/S0960-9822(18)31608-7 DOI: 10.1016 / j.cub.2018.12.007