What is Microsleep? (Symptoms, Causes and Prevention)

By: SleepScore Labs  |  June 8th, 2021

You’re driving back home, exhausted after a long week of work filled with many sleepless nights, and you suddenly realize you don’t remember the last mile of driving. You can’t recall the last red light or even the last 10 seconds. The last thing you remember is your eyelid drooping and your head bobbing. It’s almost as if you just had a fleeting moment of unconsciousness: sleep. What just happened? You may have just experienced a microsleep.  

Microsleep Defined

Microsleep is an involuntary, temporary, and short episode of sleep that usually lasts between 1 to 15 seconds. These microsleep episodes often occur when a person is trying to fight off sleeping to remain awake following extreme bouts of drowsiness. During a microsleeping episode, the brain essentially takes control of our conscious state causing a switch from wakefulness to sleep, manifesting as a complete failure to respond accompanied by slow eye-lid closure and head nodding. Researchers have found that microsleeping episodes cause dramatic changes in brain activity. Often, however, these changes are contained to certain areas or structures and are not widespread across the whole brain. For example, studies have shown that the thalamus, an area of the brain responsible for interpreting incoming sensory signals, is significantly disturbed and less active during microsleeps. In other words, certain parts of the brain may remain vigilant while other areas – particularly those involved in interpreting various signals – may temporarily shut down. Scientists refer to this process as local sleep.  

Another example of local sleep occurs when we sleep in new environments. Have you ever found yourself waking up unrefreshed after the first night of sleeping in a new hotel, or even as a child during sleepovers? This is called the first-night effect and researchers have found that one brain hemisphere remains more vigilant than the other as a kind of “night watch” to monitor unfamiliar surroundings while sleeping. Humans aren’t the only species that show signs of local sleep. For example, dolphins, seals, and manatees all exhibit uni-hemispheric sleep (sleeping one brain hemisphere at a time) allowing them to have the simultaneous benefits of sleep, vigilance, and surfacing to breathe. Similar to the survival benefits of unihemispheric sleep, microsleeps may result from the body’s dire need to sleep – while still sustaining enough vigilance to re-awaken after several seconds, and even providing a quick boost in attention. Unfortunately, an involuntary period of sleep triggered by sleep deprivation while driving may come at a tremendous cost – our safety. 

What Causes Microsleeps? 

To fully understand what causes microsleeps, it’s important to first understand what initiates “normal” sleep. Our need to sleep is caused, in part, by wakefulness: what goes up (wakefulness) must come down (sleep). The need to sleep after being awake for a prolonged period of time is known as sleep pressure. Sleep pressure is generated by the build-up of a chemical known as adenosine flooding the brain which directly contributes to sleepiness. The longer we stay awake, the more adenosine builds up, and the greater the sleep pressure is. Episodes of microsleeps are triggered by our inability to stave off this sleep pressure after being awake for a long period of time, often as a result of sleep deprivation. This means that those who are sleep deprived due to a sleep disorder like insomnia or other medical conditions are more likely to experience microsleeps than those achieving 7 to 9 hours of sleep a night.  

It’s not just sleep deprivation that can cause microsleeps – long periods of boring tasks can, too. Authors of a study published in the journal Human Brain Mapping had twenty healthy normally-rested participants perform a continuous tracking task for nearly 1 hour. The study showed that 70% of the participants engaging in the long, arduous task exhibited frequent microsleeps. Another study found that microsleeps may actually provide a benefit in terms of attenuating the need for sleep. In participants who were intentionally sleep deprived, errors and lapses in attention immediately following microsleeps were improved when compared to before the microsleep. These lapses in judgement and attention caused by microsleeps can be dangerous, particularly if they occur while driving. 

The Dangers of Microsleeps 

Microsleeps and drowsy driving significantly increase the risk of traffic accidents. Several studies have shown that sleep deprived drivers make as many, if not more, errors as legally drunk drivers. According to the Centers for Disease Control, one in every 24 adults say they’ve fallen asleep while driving at least once over the previous month. Drowsy driving is estimated to contribute to over 20% of fatal crashes in the United States every year, or up to 6,000 deaths. Important cognitive functions such as attention, decision making, vigilance and coordination all buckle under the pressure of sleep deprivation – and these effects are compounded during microsleeps. At 60 miles per hour, a driver can reach nearly 500 feet in just 5 seconds (the average length of a microsleep). One can only imagine the damage that can be caused by experiencing a microsleep on the highway. It’s for these reasons that drowsy driving, microsleeps, and sleep deprivation remain a significant contributor to road trauma and death worldwide. 

How to Avoid Microsleeps from Occurring 

Fortunately, the likelihood of microsleeps can be drastically reduced by obtaining sufficient quality sleep (between 7 to 9 hours, for most people). Ensure you get sufficient sleep leading up to big trips in order to limit your sleep debt. If, however, you are already driving with limited sleep, you must recognize the warning signs of sleep deprivation and any potential impending microsleeps including: 

  1. An inability to keep your eyes open 
  2. Blinking frequently or intensely 
  3. Excessive yawning 
  4. Brain fog and difficulty concentrating 
  5. Muscle jerks (also known as hypnic jerks) 

If you experience any of these symptoms, think about pulling over to a safe location to avoid the risk of harm or injury. If there is another rested passenger in the car, you can also take turns driving. A 20 to 30-minute nap may also provide a short-term boost to mood, alertness, and cognitive performance. According to a 1994 NASA study, sleep-deprived pilots who were allowed to take a 40-minute planned nap before a long-haul test flight experienced significantly less microsleeping episodes compared to the non-nappers. Caffeinated beverages may also stave off symptoms of sleep deprivation, but only temporarily. One cup of coffee (approximately 80 mg of caffeine) has been shown to significantly improve driving performance and self-reported sleepiness during monotonous driving for up to 2 hours.   

However, it’s critical to remember that a short nap or caffeine cannot fully replace or restore performance levels relative to a complete 7 to 9-hour sleep period. The most effective method for avoiding microsleeps is prevention. As Benjamin Franklin once said, “If you fail to plan, you are planning to fail!” Indeed, sleepless nights come at a significant, yet preventable, cost. 

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Sleep well! 

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