Microsleep Perplexes Neuroscientists

microsleep, sleep, highway hypnosis

Anyone who has ever nodded off on their feet, snapped their head forward after nearly dozing off, or stared blankly into space has experience with one of neuroscience’s more perplexing phenomena: microsleep. Microsleep happens when all or part of the brain falls briefly asleep. Though microsleep itself is common and usually benign, depending on the context in which they happen they can have deadly consequences.

Microsleep events are defined as brief and unintended lapses in attention that last between a few seconds to a few minutes. Colloquially, microsleep may also be referred to as “nodding off” or specifically as “highway hypnosis” when referring to microsleep events that happen while a person is driving. Signs of a microsleep event include staring blankly off into space, nodding of the head (which may lead to the familiar “snap back to attention”) and acting on “autopilot”. A person on the verge of a microsleep event may experience stinging sensations in their eyes, which stimulates more frequent and slower blinking. While some people close their eyes during microsleep, others will have their eyes open and appear otherwise alert as normal. In fact many microsleep events go unnoticed—even by the person who is experiencing them.

Most importantly, people experiencing microsleep will not react to outside information. This is especially dangerous when a person is driving. “Highway hypnosis” has been blamed as a reason why people fail to see red lights, stop signs, or curves in the road. Though microsleeping can happen at any time of the day or night, people are at a particular risk in the hours before dawn and in the afternoon. This is because the many people’s natural biorhythms prompt the body to become fatigued at these times. Accordingly, insurance companies have observed that most fatigue-related accidents happen either in the afternoon or between 2:00 and 6:00 in the morning.

microsleep, sleep, highway hypnosis

Microsleep events are more common in people suffering from sleep deprivation. They are particularly likely to occur while a sleep deprived person is performing a monotonous task such as driving for an extended period of time, watching a computer screen, or sitting in on an un-engaging meeting or lecture. While some researchers suggest that the whole sleep-deprived brain shuts off with lack of stimulation, others argue that parts of the brain can selectively fall asleep.

Although virtually everyone will at one point or another experience a microsleep event, these phenomena pose a perplexing puzzle for neuroscientists. To date, observing microsleep events remains a challenge due to the brief nature of the episodes and the unresponsive nature of the subjects. German scientists have attempted to identify microsleeping by looking for distinct “alpha events” that occur in a fatigued person’s brain. Other researchers have used psychomotor vigilance tasks and eye tracking technology to try and observe when a person’s alertness wanes. Even Mercedes-Benz has sought to find a reliable way to detect these phenomena early on. The automotive company hopes to be one of the first to introduce fatigue-detection technology into its cars. Such smart technology would sound an alarm if the driver shows signs of fatigue based upon his or her driving patterns, the rate and frequency of blinking, the time of day, and length of the journey.

By Sarah Takushi


American Academy of Sleep Medicine

CHEST Journal

Chronobiology International






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