Experts Find Only Partial Overlap Between Sleep Trackers, Sleep Science

smart tech is often inaccurate and limited in scope

By Jonny Lupsha, Wondrium Staff Writer

Sleep-tracking smart tech and similar apps aren’t quite all they claim to be, an article by HuffPost says. They can often be inaccurate and fairly limited in the information they provide about sleep patterns. Their real benefits are limited, but not nonexistent.

Woman asleep in bed with smart watch sleep tracker showing
Wearable sleep trackers give limited information about sleep patterns; whereas, rigorous neurological studies measure slow-wave brain activity to discover the function of sleep. Photo by Andrey_Popov / Shutterstock

According to the HuffPost article, tech like wearable sleep trackers and related smartphone apps oversell themselves a considerable amount. For example, a section on their inaccuracy points out that a restless sleeper may toss and turn, leading their tracker to believe that the person is awake. However, they can give you insight into your personal sleep habits and provide a first step on the path to neurophysiological health.

Low-Frequency Electrical Activity in the Brain

In order to understand the science of sleep, the first step is to make sense of non-REM (Rapid Eye Movement) sleep, neurologically speaking. The best way to define non-REM sleep is in relation to an electroencephalogram (EEG) test, which measures the brain’s electrical activity moment to moment.

“Non-REM sleep [is] the EEG slow-wave activity which we also call delta power,” said Dr. H. Craig Heller, the Lorry I. Lokey/Business Wire Professor of Biological Sciences and Human Biology at Stanford University. “Delta power is a measure of how much the EEG is dominated by brain waves at the very low frequencies between 0.5 and 4.5 hertz. The important fact is that the magnitude of delta power is determined by the duration of prior wakefulness—thus, delta power seems to be a measure of sleep need, a measure of the homeostatic drive for sleep that builds up during wakefulness.”

In other words, the time we spend in non-REM sleep can be accurately measured by an EEG test. The EEG quantifies non-REM sleep by measuring low-frequency electrical activity in the brain. The duration or strength of this low-frequency activity seems to be a direct response to the amount of time we spent awake before it. It’s a dense knot to untangle, but also an indicator of what sleep trackers can—and can’t—tell us.

Unlocking the Mysteries of Sleep

Why do we worry so much about our sleep patterns anyway? Any adult knows how much better they function after a full night’s sleep, so shouldn’t we just try to get around eight hours and have an extra cup of coffee when we don’t? As it turns out, the reasons why we sleep are still a mystery on several levels, but looking more closely at non-REM sleep and delta power may help answer this deceptively obvious question.

“If we understood the cellular mechanisms that cause these EEG changes—these changes in slow-wave activity that we’re interested in—that understanding should bring us closer to discovering the function of sleep,” Dr. Heller said. “First, it is safe to assume that a function of sleep has to involve mechanisms at the cellular level. Second, the EEG measures we have been discussing are reflecting activity of the brain, but the mechanisms underlying those brain wave patterns are properties of the billions and billions of neurons that make up the brain.”

Dr. Heller said that, therefore, wakefulness is causing some kind of cellular change in the brain cells that influence brain activity during sleep, but this change is somehow reversed by sleeping. “The bottom line is that if we understand the cellular processes underlying the generation of slow-wave activity in the EEG, that knowledge should bring us closer to the cellular changes produced by wakefulness and reversed during sleep,” he said. “Those changes should be at the very core of the function of sleep.”

So, although sleep trackers can give us a clue as to how much we’re sleeping and in which states, this information pales in comparison to the deeper knowledge attainable through rigorous neurological study. And, we still lack answers for the greater mysteries of sleep.

Dr. H. Craig Heller contributed to this article. Dr. Heller is the Lorry I. Lokey/Business Wire Professor of Biological Sciences and Human Biology at Stanford University

Dr. H. Craig Heller contributed to this article. Dr. Heller is the Lorry I. Lokey/Business Wire Professor of Biological Sciences and Human Biology at Stanford University. He earned his Ph.D. in Biology from Yale University.