Originally published on Van Winkle's (May 2016)

Lighthearted stories and lullabies eventually do the trick. But few things send a child to sleep as well as a simple rocking motion. Be they in a crib or curled in grandma's swaying arms, a tired child usually conks out pretty quick. Yet, as anyone who's nodded off on a moving train can attest, there's something about a gentle rocking motion that induces drowsiness. But why?

University of Geneva researcher Sophie Schwartz knows. In a 2011 study, the results of which were published in Cell, she and her colleagues enlisted volunteers to nap for 45 minutes on a custom-made "experimental hammock." In some cases the hammock swayed, in others it was still. Whenever it rocked, participants fell asleep faster and deeper. 

"We observed a faster transition to sleep in each and every subject in the swinging condition," said co-researcher Dr. Michel Muhlethaler, also from the University of Geneva. Sleep-related brain waves showed a "dramatic boosting" as the bed swung side to side. Interestingly, the rocking was performed at a fairly slow speed, oscillating every four seconds. Rocking at this pace increased the rate of Stage 2 sleep and increased sleep spindles, both indicators of deep relaxing shut eye. 

The researchers have hopes that rocking may play for individuals with brain damage, such as a stroke. They also want to expand their investigation into seeing if rocking would help people with insomnia. 

Although this study establishes the relationship between rocking and sleep, some scientists propose a more fundamental question.

"I agree with the researchers' hypotheses about rocking affecting brain centers, and yet I also think it is important to address the deeper level of why it is that rocking might have such an effect. I think it is not just mechanical," said behavioral sleep expert and founder of Sleep Easily, Richard Shane, PhD. 

"Rocking connects us with natural rhythms of life such as heartbeat, day/night, tides, cycles of the moon, seasons," said Dr. Shane. "This helps us feel less separate, and more connected with something fundamental, and from that more secure."

He believes this sense of security may even harken back to out earliest experiences -- being in the womb and sensing our mother's pattern of inhalation and exhalation.

So, now that summer is approaching, dust off the hammock and get swaying. You might find that with a little to and fro, your brain will send you to sleep for a sweet bit of dreamless bliss.