Our ability to concentrate is directly impacted by even the smallest amount of sleep deprivation, Matthew Walker observes in his powerful book, Why We Sleep: Unlocking the Power of Sleep and Dreams.

“The deadly societal consequences of these concentration failures play out most obviously and fatally in the form of drowsy driving,” he writes.

Car collisions are one of the leading causes of death in most first-world nations. In the U.S., someone dies in a traffic fatality every hour due to a fatigue-related error.

There are two causes of drowsy-driving accidents. The first is more widely understood: people who fall asleep entirely while driving. Fortunately, these types of accidents happen infrequently and typically result from the driver being “acutely sleep-deprived (having gone without shut-eye for twenty-plus hours),” explains Matthew.

The second type of accident is not well understood but is much more common. It results from a “momentary lapse in concentration, called a microsleep,” Matthew writes. “These last for just a few seconds, during which time the eyelid will either partially or fully close. They are usually suffered by chronically sleep-restricted individuals, defined as getting less than seven hours of sleep a night on a routine basis.”

During a microsleep, our brains become “blind to the outside world for a brief moment—and not just the visual domain, but in all channels of perception,” Matthew explains. “More problematic is that [our] decisive control of motor actions, such as those necessary for operating a steering wheel or a brake pedal, will momentarily cease.”

In other words, we don’t have to fall asleep for ten seconds while driving to cause a deadly accident. A two-second microsleep at 30 mph with a modest drift into the next lane can have dire consequences.  

What makes these incidents even scarier? Many times we have no awareness that it ever happened.  

A 2016 large-scale study by the AAA Foundation of over 7,000 drivers in the U.S. detailed the catastrophic impact of drowsy driving. Operating on less than five hours of sleep, our risk of a car crash increases 3X. When we’ve had less than four hours of sleep, we are 11X more likely to be involved in an accident.

“Note how the relationship between decreasing hours of sleep and increasing mortality risk of an accident is not linear, but instead exponentially mushrooms,” Matthew writes. “Each hour of sleep lost vastly amplifies that crash likelihood, rather than incrementally nudging it up.”

Professor David Dinges of the University of Pennsylvania has conducted in-depth research on sleep deprivation. One study divided subjects into four groups: Group one was kept up seventy-two hours straight (i.e., no sleep for three consecutive nights). Group two was allowed four hours of sleep per night. Group three had six hours. Group four had the recommended eight hours.

To measure concentration, David had the participants press a button in response to a light on a button box or computer screen. The response and reaction times were both measured. “Thereafter, another light comes on, and you do the same thing,” Matthew writes. “The lights appear in an unpredictable manner, sometimes in quick succession, other times randomly separated by a pause lasting several seconds.  

“Sounds easy, right? Try doing it for ten minutes straight, every day, for fourteen days,” Matthew observes.

There were several findings. First: participants would, for brief moments, stop responding altogether, i.e., microsleeps. “Slowness was not the most sensitive signature of sleepiness; entirely missed responses were,” Matthew explains. “The real-life equivalent of which would be failing to react to a child who runs out in front of [our] car when chasing a ball.”

The results? Individuals in group four who slept eight hours every night “maintained a stable, near-perfect performance across the two weeks,” writes Matthew. “Those in the three-night total sleep deprivation group suffered catastrophic impairment, which was no real surprise.”

The biggest surprises involved the other two groups.  

For group two, the four hours of sleep group, after six nights, “participants’ performance was just as bad as those who had not slept for twenty-four hours straight—that is, a 400 percent increase in the number of microsleeps. By day 11 on this diet of four hours of sleep a night, participants’ performance had degraded even further, matching that of someone who had pulled two back-to-back all nighters, going without sleep for forty-eight hours.”

Most worrisome from a societal perspective were the results from group three, those who had six hours of sleep a night (which may sound familiar to many of us): “Ten days of six hours of sleep a night was all it took to become as impaired in performance as going without sleep for twenty-four hours straight.”

When study participants were asked how diminished they were, they “consistently underestimated their degree of performance disability,” Matthew notes. “It was a miserable predictor of how bad their performance actually, objectively was.

“With chronic sleep restriction over months or years, an individual will actually acclimate to their impaired performance, lower alertness, and reduced energy levels. That low-level exhaustion becomes their accepted norm or baseline.

“Based on epidemiological studies of average sleep time,” Matthew reasons, “millions of individuals unwittingly spend years of their life in a sub-optimal state of psychological and physiological functioning, never maximizing their potential of mind or body due to their blind persistence in sleeping too little.”


Reflection: Am I getting enough sleep regularly? If not, what am I going to do about it?

Action: Journal about my answers to the questions above.

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