Anyone who’s had trouble dozing off has most likely tried any number of bedtime tricks, be it downing a dose of melatonin, sipping chamomile tea or pulling out the yoga mat. When we sip, stretch or simply slow the hell down, we’re trying to jog our brains into entering its normal sleep cycle. Some scientists think we can do an even better job by hacking the way we hear.
Sleep is directly related to the behavior of brainwaves. As we pass through the various stages of sleep, alpha, beta and theta waves hover between one and nine hertz in frequency. Light sleep is associated with waves between one and nine hertz; the transition into deep sleep sees frequencies drop to right around two; deep sleep cycle frequencies fall below that.
A method known as brainwave entrainment seeks to incite this natural sleep cycle by tricking brainwaves into producing these slumber-friendly frequencies. The secret to gaming this complex system? Stereo audio.
Before unpacking how sound can influence brainwaves, let’s take a step back and break down how we hear. In real life, our right and left ears each hear slightly different versions of sounds; those disparities help our brains determine where a car horn, crying baby or Mr. Softee truck might be.
“A sound that's on your right side will reach your right ear before it reaches your left ear,” explains Joy Lyons, an audio engineer and CTO of Ossic, a startup developing 3D audio technologies for headphones. “Some of the sound will have to bend around your head to get to the other side, and so your left ear will have some level differences. Your brain uses that information to help localize sound.”
Entrainment influences brainwave activity by taking advantage of this ever-present internal frequency-crunching. The changes created are referred to as binaural beats. To experience them, you only need a pair of headphones. Dozens of products and downloadable audio tracks use the method to help users reach meditative states or heighten concentration, while others, like Sleep Salon and Sleep Shepherd, promise a better night’s ZZZs.
To coax brainwaves into a sleep cycle, systems play back inaudible frequencies on top of music. For example, one ear might hear a frequency of 404 hertz while the other hears 408 hertz. As those signals merge, they create a four-hertz wave, inducing a rhythm that brainwaves then mimic. The Sleep Shepherd, in particular, uses onboard EEG sensors to track progress, and shifts its target frequency based on the wearer's stage of sleep at a given moment as well as the next stage they should enter.
Although neurologists have yet to identify precisely why the method works, a handful of studies have made some headway in verifying its efficacy. Vera Abeln, a post-doctoral researcher and lecturer at the German Sport University in Cologne, conducted a pilot study with the Sleep Shepherd in 2013. She measured the effectiveness of brainwave entrainment on a group of elite youth soccer players, whose high levels of stress and activity could contribute to irregular and low-quality sleep patterns. After eight weeks, her subjects were able to fall asleep more quickly and experienced an improvement in overall sleep quality.
While the subjects of Abeln’s study were aware of its goal, she doesn’t think the placebo effect or confirmation bias are at work. “I’ve seen studies with babies and with the elderly — people who are not really thinking about what is going on — have very good results,” she says. “In fact, in these groups, [brainwave entrainment] seems to work better than in others.”
Still, the results cannot be guaranteed, nor is entrainment a cure for insomnia or other conditions over the long term.
“Entrainment is a temporary effect on the synchronization of neuronal firing,” writes clinical neurologist Steven Novella. “It does not improve or increase brain functioning, it does not change the hardwiring, nor does it cure any neurological disorder.”
Abeln freely admits that more research is needed to solidify the method’s usefulness for the general population and hopes to conduct a follow-up study with a larger sample and a control group. In the meantime, however, there is good news. Her study found that entrainment works its best when the user is able to select her or his own backing track. A little Adele to play out the day? Yes, please.