By Dr. Stijn Massar
The mysteries of sleep have piqued human curiosity since the beginning of time. What happens when we sleep? Where does the mind travel to when we dream? How do we falter when we stay awake without sleep? Artists, philosophers, and scientists in societies across all of human history have had their ideas about the workings and functions of sleep.
While societies throughout history have had their tradition of inquiry, modern day sleep science sprung up about a century ago. In 1924, the first recording of electrical brain activity from the human scalp was made. While initially received with hesitation, this major technological innovation made it possible, for the first time, to measure the human brain in action. The identification of different brain activity patterns during sleep led to the classification of different sleep stages. Most famously, Eugene Azerinsky and Nathaniel Kleitman described a stage called Rapid Eye Movement sleep (REM), often referred to as “dream sleep”, that was characterized by awake-like brain activity and fast eye movements in an otherwise immobile body.
Kleitman was a real pioneer in pushing the science of sleep. In order to study the effects of external time cues, he spent a month in a cave, isolated from sunlight and other influences, trying to adopt a non-standard, non-24h, rhythm (not unlike rotating shift schedules). The method of polysomnography (multimodal physiological monitoring including brain activity, heart rate, respiration, and muscle activity) is still considered the gold standard of sleep measurement today. Yet, the intensive nature of the physiological measurement makes it such that polysomnography is often restricted to short term monitoring of individual patients, often in specialized laboratories.
To study sleep patterns in larger populations, and in more natural circumstances, researchers turned to actigraphy. Wearable devices that track physical activity demonstrated the potential to estimate periods of wake (high activity) and sleep (low activity). These devices could be worn for longer periods of time, without interfering with normal routines. Given these possibilities to measure habitual sleep patterns, actigraphy soon became part and parcel of sleep science.
While research-grade actigraphs proved useful, they remained relatively expensive and limited in the information they could capture (sleep staging was not possible). With the latest boom in consumer technology, however, came a strong drive to improve sensors and algorithms. Wearable devices have been made more powerful, more user friendly, and much more affordable. This allows for the detailed study of natural sleep patterns in hundreds, thousands, or even hundreds of thousands of people simultaneously, and the documentation of population-wide shifts in sleep (for instance due to restrictions related to the COVID-19 pandemic, see our work for more).
The use of consumer wearables brings along its own set of challenges, and the technology is ever developing. Yet, the depth of information that can be gathered, along with the scale of measurement, presents an unprecedented opportunity to advance sleep science. By participating in this study, you are truly contributing to pushing the boundaries of current knowledge.