The SleepLoop system developed by ETH researchers emits a sound at the right time to amplify the slow brain waves

Deep sleep phases encouraged using wearable headband

Image credit: SleepLoop

Researchers at ETH Zurich have developed a wearable device that plays specific sounds to help enhance deep sleep.

Many people, especially the elderly, suffer from abnormal sleep. In particular, the deep sleep phases become shorter and shallower with age.

Experts say deep sleep is important for the regeneration of the brain and memory and has a positive influence on the cardiovascular system.

Researchers have shown that the brain waves characterising deep sleep - so-called slow waves - can be improved by playing precisely timed sounds through earphones while sleeping.

While this works well in a sleep laboratory under controlled conditions, there has so far been no at-home solution that can be used longer than just one night.

Now researchers at ETH Zurich have developed a mobile system that people can use at home, which aims to promote deep sleep through auditory brain stimulation.

The SleepLoop system comprises a headband that is put on at bedtime and worn throughout the night. This headband contains electrodes and a microchip that constantly measures the brain activity of the person sleeping. The headband autonomously analyses data from this in real-time on a microchip using custom software.

As soon as the sleeping person shows slow waves in the brain activity characterising deep sleep, the system triggers a short auditory signal (clicking). This helps to synchronise the neuronal cells and enhance the slow waves.

Researchers from ETH Zurich and University Hospital Zurich, led by Caroline Lustenberger, group leader at the Neural Control of Movement Lab, have conducted a clinical study with this device for the first time.

The study involved equipping participants, between 60-80 years old, with the SleepLoop system, which they were required to operate themselves in their own homes.

Lustenberger said the system functions independently, even for users with little technical experience. “This worked very well. We had little data loss and the participants rated the device as user-friendly,” she explained.

Participants wore the device every night for four weeks, with the auditory stimulation given nightly for two weeks and no stimulation for the next two weeks. Neither the subjects nor the researchers knew in which two weeks the auditory signals were played and in which two they were not.

The results of 16 participants of the study showed that it was possible to enhance the slow waves through auditory signals during deep sleep in most participants. But individual differences were extensive, with some subjects responding very well to the stimuli, while others responded minimally or not at all.

According to Lustenberger, the question of whether a person reacted to a stimulus did not depend on their wellbeing during the day. “Some people generally responded well to the stimuli and demonstrated enhanced slow waves, while others showed no response regardless of their daily wellbeing.”

The researchers have used these individual differences to better predict how an individual will respond to the auditory stimulus. This will help the team optimise and improve the performance of SleepLoop.

A spin-off company to the university, Tosoo AG, is currently working on developing the device further and preparing it for the clinical market.

“This is a medical device, not just a wellness consumer product you can order online when you have trouble sleeping,” said Walter Karlen, who developed the technology at ETH Zurich. “Use of the device must be medically shown and supervised by a doctor.”

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