We know rocking works: this is how we get babies to sleep, this is how we fall asleep on a swinging hammock by the beach, this is how we fall asleep in subway trains. But how does it work? Does it relax us somehow? It turns out there is something even much more interesting going on! It turns out that rocking induced an increase in brain activity associated with deep sleep. The scientists think that rocking causes a synchronization of brain waves in the areas associated with sleep. I feel like taking a nap just reading about this.
Rocking synchronizes brain waves during a short nap
Laurence Bayer1, ∗, Irina Constantinescu1, ∗, Stephen Perrig2, Julie Vienne3, Pierre-Paul Vidal4, Michel Mühlethaler1, ∗, and Sophie Schwartz1, 5, ∗,
1 Department of Neuroscience, University of Geneva, Switzerland
2 Sleep Laboratory, Geneva University Hospital, Switzerland
3 CIG, University of Lausanne, Switzerland
4 CNRS, UMR 8194-Université Paris Descartes, France
5 Swiss Center for Affective Sciences, University of Geneva, Switzerland
∗ These authors contributed equally to the work.
Why do we cradle babies or irresistibly fall asleep in a hammock? Although such simple behaviors are common across cultures and generations, the nature of the link between rocking and sleep is poorly understood [1,2]. Here we aimed to demonstrate that swinging can modulate physiological parameters of human sleep. To this end, we chose to study sleep during an afternoon nap using polysomnography and EEG spectral analyses. We show that lying on a slowly rocking bed (0.25 Hz) facilitates the transition from waking to sleep, and increases the duration of stage N2 sleep. Rocking also induces a sustained boosting of slow oscillations and spindle activity. It is proposed that sensory stimulation associated with a swinging motion exerts a synchronizing action in the brain that reinforces endogenous sleep rhythms. These results thus provide scientific support to the traditional belief that rocking can soothe our sleep.
Scientific American reports on this, through a delightful 60-second podcast
You’re lying in a hammock by a breezy shore. The hammock rocks softly back and forth. In no time…(snoring). It turns out that’s not just the relaxation of being on vacation that’s bringing on sleep. It’s the rocking hammock. That might not be a huge surprise—babies get rocked to sleep. But researchers wanted to know how rocking works.
They recruited 12 healthy males, all good sleepers. Each volunteer twice took an afternoon nap in a dark room on a custom-made bed that could rock. For one nap, the bed was still. For the other, it rocked gently.
The authors speculate that there may be 3 mechanisms at play that explain the change in sleep-related brain activity induced by rocking: 1) vestibular (the system that deals with balance spatial orientation) and and somatosensory pathways are actually anatomically linked to the amygdala (linked not only to emotions but also to the awake/sleep transition); therefore the rocking motion could indeed induce a faster awake/sleep transition by "relaxation" through the amygdala; 2) the rhythmic vestibular and somatosensory inputs caused by rocking could modulate sleep-wake brain centers through direct (or indirect) connections between sensory systems and the hypothalamus and/or brain stem (both involved in regulating the sleep cycle); or 3) the rocking sensory inputs could affect the synchrony of neural activity in thalamo-cortical networks (both somatosensory and vestibular inputs go directly to thalamic nuclei (groups of neurons in the thalamus).Previous experiments have shown that slow rhythmic cortical stimulation was recently found to increase EEG slow oscillations and spindles, both hallmarks of deep sleep. The authors speculate that this third option is the most likely explanation, because they also observe an increase in slow oscillations and spindles.
Sight, Sound, Touch, Taste, & Smell.
The Sixth sense is portrayed as supernatural.
Balance is forgotten.
The Vestibular/Inner ear system (Saccades/Utricle).