WE ALL know the awful hangover from a bad night’s sleep: tiredness, crotchetiness, poor concentration and sluggish reactions. Thankfully, these can all be fixed by catching up on your zzz’s the following day, but if sleep continues to evade you, trouble is coming. Chronic insomnia can lead to severe health problems, including obesity, type 2 diabetes and depression.
Such a lack of rest is a major issue. The amount of sleep people need varies, with most adults requiring between 7 and 9 hours each night. But a lot of us fail to hit that target on a regular basis. According to the US Centers for Disease Control and Prevention, about , and around 20 per cent have chronic sleep conditions.
Advertisement
“Sleep is such a problem,” says at the Medical University of South Carolina. “It would be great if we had some kind of device that would help people.”
Of course, there is no shortage of apps and gadgets that claim to monitor and analyse your sleep, but after decades of mixed results, recent breakthroughs in brain stimulation are about to take things a step further. A range of products that directly interact with your brainwaves are promising to help hack your sleep for a better night’s rest. But can they really live up to their potential?
The first stirrings of “consumer sleep technology” arrived in 2005, when a company called Zeo launched a headband that purported to record and analyse sleep and give advice on how to improve it. Zeo was ahead of its time and folded around 2012, but, by then, had launched its first product, the Fitbit Tracker. Primarily marketed as an activity monitor, it also claimed to measure sleep. Similar devices followed, as did non-wearable technologies. These “nearables” included smartphone apps that eavesdrop on breathing and movement, and sensor-packed gadgets to put on the bedside table or under the mattress. A by the US National Sleep Foundation and Consumer Electronics Association found that almost a quarter of US consumers owned sleep-tracking technology. In 2020, experts .
One goal of these devices is to record the duration and quality of sleep, in order to provide feedback to help users improve it.
How to track sleep in the lab
In a sleep lab, this is done through a technique called . A PSG typically involves being wired up to an electroencephalogram (EEG) machine – to record brain activity – plus various other devices that track eye movements, muscle tension, heart rhythm, breathing patterns and blood oxygen level. The outputs are later analysed by a specialist, who breaks the night’s sleep down into 30-second segments called epochs and judges whether the subject was awake or not during them. The technology can also be used to judge if someone is in rapid eye movement (REM) sleep, in which we have our most powerful dreams, or non-REM sleep, thought to be important for the consolidation of learning and for clearing toxins that build up in the brain.
PSG is described as the “gold standard” of sleep measurement, but has drawbacks. It is expensive, time consuming, can’t be used outside a lab and often disrupts sleep. It also needs experts to operate the equipment and interpret the data. Even then, researchers often score the same epoch differently.
There is an established alternative called actigraphy, which uses accelerometers in a wristband to record physical activity throughout the night. This is a fairly reliable way to tell whether somebody is fully awake or asleep, though it can’t recognise different sleep stages and often overestimates duration of sleep, as it has difficulty distinguishing it from calm wakefulness. Nonetheless, actigraphy overcomes some of the downsides of PSG – it can be used outside the lab, for example, and over multiple nights – and has proved a useful if somewhat blunt tool.
Sleep tracking at home
Most of the first-generation consumer sleep-tracking technologies were based on the same principles as actigraphy. Some later versions added thermometers, heart-rate monitors and , which measure blood oxygen level. All three can increase the accuracy of the device because body temperature, heart rate and the amount of oxygen in blood . But they are only proxies for what is going on in the brain.
Unsurprisingly, these to bring lab-grade sleep tracking to the bedroom. But as the technology improved, so did its accuracy. Several have found that some current consumer devices perform at least as well as standard actigraphy, though they still can’t compare to PSG. A 2020 , for example, put seven commercial devices through their paces against lab-grade equipment. For three nights, volunteers tested four wristbands and three nearables in the sleep lab at the US Naval 91ɫƬ Research Center (NHRC) in San Diego, California. All but two performed just as well as or better than actigraphy.
Until recently, however, such head-to-head comparisons were performed under laboratory conditions and were uninformative about sleep tracking in the real world. So, earlier this year, the same team, led by Evan Chinoy at the NHRC, .
They got 21 people to simultaneously wear four devices – two wristbands, a watch and a ring – at night and as much as possible during the day. They also wore a research-grade actigraphy monitor and an EEG headband at night for comparison. The participants lived freely at home and could choose when to sleep. The only restriction was no alcohol. After a week, the researchers analysed the data from all the consumer wearables, which comprised the Fatigue Science ReadiBand, Fitbit Inspire HR, Polar Vantage V Titan and the Oura Ring.
On the whole, all four performed well, especially at detecting sleep versus wakefulness and on a metric called sleep efficiency, which is the percentage of time in bed actually spent asleep. Ideally, this should be around 90 per cent, says of the Sleep and 91ɫƬ Research Program at the University of Arizona.
Of course, it is one thing to gather accurate data about your own sleep, but quite another to act on it. Many sleep devices offer coaching based on the data they collect, but, as Grandner puts it, “just as a bathroom scale is not a weight loss programme, a sleep tracker is not a sleep improvement programme”.
However, some newer devices do go further and intervene during sleep on behalf of consumers through a relatively elementary nudge. The , for example, cools down when it is time to nod off (being a bit cold promotes sleep) and warms up in preparation for waking, while the detects snoring and adjusts the snorer’s head position to open their airway.
How to improve your sleep
Other interventions are responsive to sleep itself. , for example, shine infrared light into the ears to monitor heart rate, and when they detect that the wearer is drifting off to sleep, they fade out any audio. They also mask nocturnal disturbances such as snoring with gentle nature sounds or pink noise, a variant of white noise that .
Despite these advances, however, not much is known about the real-world benefits of using sleep trackers. of a wristband called WHOOP in 32 people aged between 18 and 28 found that using it for a week improved how they perceived their sleep quality. Seemingly paradoxically, it also reduced sleep duration, perhaps because the device advised them to sleep a little less. The two findings aren’t necessarily contradictory: is an established therapy for insomnia because it makes people sleepier.
But whether such small gains actually make a difference is debatable, says Grandner. “In general, these effects may be weak and limited to those without much need for intervention.”
Population-level data suggests he is right. The US National Sleep Foundation publishes an annual , which assesses sleep quality across a representative sample of the US population and converts it into a score out of 100. The 2014 edition gave US citizens an average score of 76. In 2021, it was 76.1.
There is even evidence that the use of sleep trackers can be counterproductive, leading people to become preoccupied with perfecting their sleep, ironically causing insomnia.
That said, consumer sleep technology now looks to be entering a new phase that may, finally, deliver on its initial promise of gold-standard tracking at home – and perhaps exceed it by intervening on a whole new level to improve sleep.
Hacking your brainwaves
The start of this revolution is a new generation of research-grade sleep trackers designed to combine the detail of PSG with the convenience of actigraphy. The , made by Advanced Brain Monitoring in California, for example, uses EEG to record brain activity and an array of other sensors for heart rate, muscle tone, eye and body movement and sound, all built into a headband that can be worn at home. The US Food and Drug Administration (FDA) has deemed it to be “substantially equivalent to PSG”. Another is the , made by a French company of the same name. It features EEG sensors, a pulse oximeter, a heart rate monitor and an accelerometer, and can also be worn at home. In 2020, a peer-reviewed study .
Also in the pipeline are EEG sensors placed in or around the ears. These aren’t as sensitive as those used in lab-based PSG, but have been shown to , which reflect what stage of sleep a person is in.
The commercial potential of such devices isn’t lost on their manufacturers. Sleep Profiler isn’t on sale, but Dreem briefly marketed a consumer version of its headband. Electronics giant Philips also trialled a similar headband called , after a showed a small but significant effect on sleep quality. However, Philips appears to have discontinued the product and didn’t respond to requests for further information.
But now comes the real advancement. The Dreem 2 headband not only tracks sleep using EEG, actigraphy and a pulse sensor, but also intervenes when it detects that the wearer is coming out of deep sleep too early, nudging their brain back into this state. It does this by transmitting vibrations through the skull to the inner ear, where they are perceived as pulses of pink noise. That sounds like magic, but it builds on solid science that a .
Restoring sleep
This type of slumber – also known as slow-wave sleep – is the most restorative phase. It is characterised by long, languid brainwaves at a frequency of 4 hertz or less, and has long been seen as potentially hackable to improve sleep. In 2006, researchers at the University of Lübeck in Germany showed that they could do just that. They attached electrodes to the heads of volunteers, waited until they were drifting into deep sleep and then switched on a targeted electrical current in five 5-minute bursts separated by a minute’s rest. The result was . For this, before falling asleep, the volunteers were given a list of words to learn. When they woke up, they were asked to recall as many as they could. Those given brain stimulation performed better than those given a sham, in line with the idea that deep sleep promotes memory consolidation.
Other teams later showed that similar improvements could be achieved by stimulation with , , though the results were weak and inconsistent. “All of these attempts to drive the brain’s rhythm during slow-wave sleep by an external pacemaker were not very successful,” says , a member of the Lübeck team now at the University of Tübingen in Germany. “We think this is because the brain’s own slow oscillation rhythm is generated with a considerable jitter.” This unpredictability led Born and his colleagues to devise a system where auditory stimulation (in the form of 50-millisecond bursts of pink noise) was only applied when EEG detected that the brain had spontaneously entered a slow wave. The result of this “closed-loop” stimulation was a much stronger and longer enhancement of deep sleep and bigger memory improvements. “Imagine a swinging swing that is slightly pushed at the right moment,” says Born.
That result, published in 2013, has since been replicated in numerous labs. And while the Dreem 2 was discontinued after the company refocused on providing sleep devices for clinical trials, closed-loop technology is finding its way into other prototype wearables and consumer sleep headbands.
Some of the best evidence for the efficacy of this new approach comes from a clinical trial in older adults, who often have difficulty staying in deep sleep. at the Swiss Federal Institute of Technology in Zurich gave 16 adults, aged 62 to 78, an EEG headband called SleepLoop, which her team is developing for research purposes. The participants used the device at home for four weeks, two weeks with stimulation and two without, though nobody knew when the headbands would be in fully active mode. Lustenberger found that some of the participants had better deep sleep when stimulated, though others didn’t respond at all. Nonetheless, she says, the trial demonstrates that the technology can improve deep sleep in some older adults.
The evidence is patchy for younger people. In 2019, at the Russian Academy of Sciences Laboratory of Sleep and Wakefulness Neurobiology in Moscow on herself and a small group of volunteers aged 20 to 40, with mixed results. “A couple of them just couldn’t get used to the device,” she says. “Some reported some improvements. One participant with mild insomnia has purchased her own device and uses it constantly. I personally didn’t notice any effects, and I can’t say anything conclusive yet,” she says.
But dreams live on. Earable Neuroscience in Boulder, Colorado, recently , showing that it can speed up the onset of sleep by 24 minutes. The device – called the FRENZ Brainband – can be preordered for $490. It, too, may fall by the wayside, but closed-loop sleep systems look set to get there in the end. “I really have high hopes for this type of sleep stimulation,” says Puchkova. I’ll dreem to that.
Graham Lawton is senior features writer at New Scientist
New Scientist audio
You can now listen to many articles – look for the headphones icon in our app
