Imagine you’re doing an exceptionally boring task, like stirring the pot or folding clothes or attending a tedious lecture. Your mind started to wander and lands at an unidentified mental location, what you later call “zoning out.” Scientists have gained a better idea of what actually happens during these instances of blanking out.

Published in Nature, the new study shows the occurrence of “sleep-like activity” in the awake brain when our attentions lapse, what triggers it, and how that influences human behavior.

The phenomenon, called “local sleep,” was previously studied when our brain enters a state that resembles sleep while we’re awake — usually associated with instances we’re really tired or deprived of sleep. But the current study analyzed the brain activity of well-rested volunteers when their minds were wandering.

“The concept of local sleep builds upon a recent questioning of the classical view of sleep as an all-or-nothing phenomenon,” the team explained.

The researchers asked 26 healthy participants to take a relatively boring test, called a “Go/NoGo test.” The drill involved the volunteers staring at images of faces or numbers that change every second for over an hour. For whenever they saw a neutral face or any number other than three, they had to press a button (Go); otherwise when they saw a smiling face or the number three, they had to do nothing (NoGo).

Every 30 to 60 seconds, they were asked to report on their mental state. Naturally, a lot of people’s brains wandered off. Most of the time, they declared “thinking about something else or thinking about nothing.”

“We speculate that the slow waves we report here are generated by similar neural mechanisms as slow waves in sleep,” the study noted. “Slow waves” are known to occur during sleep signifying minimum neuron activity. “Our hypothesis was that these lapses in neuron activity could explain lapses in attention,” the researchers wrote in The Conversation.

“This new study reaffirms how sleep and wakefulness can be intermingled in the human brain,” the researchers said.

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Just as our attention varies with different tasks, there are varying degrees of attention collapse too.

The study tracked the slow brain waves in the localized areas and noted the slow waves distinguished the brain activity between “mind-wandering” and “mind blanking.” When our brain wanders, there is “rich and spontaneous” mental activity, whereas there is an absence of mental activity when our mind blanks.

“Attentional lapses occur commonly and are associated with mind-wandering, where focus is turned to thoughts unrelated to ongoing tasks and environmental demands, or mind blanking, where the stream of consciousness itself comes to a halt,” the researchers noted. So while mind wandering is still linked to high brain activity, mind blanking signifies no brain activity. Scientists have previously estimated we spend up to half our waking lives thinking about something other than the task at hand.

The study also identified what triggers a wandering, or a blanking, situation: it is triggered depending on the location of the sleep waves. Attention lapses share a common origin in the brain: the pattern of brain activity was similar to when we are about to fall sleep, occurring both in the front and back parts of the brain.

Slow waves at the front of the brain preceded mind wandering, when they occurred in regions farther back in the brain, the detection was followed by the participants reporting a blank mind. “The location of slow waves could distinguish between sluggish and impulsive behaviors, and between mind wandering and mind blanking,” the study noted.

People whose minds were “wandering” reportedly had more false alarms or incorrect clicks. On the contrary, people whose minds were blank recorded a lot more misses, i.e., not clicking when they should have.

“By monitoring people’s brainwaves against their self-reported states of attention, we found that mind-wandering seems to happen when parts of the brain fall asleep while most of it remains awake,” the researchers wrote in The Conversation.

“It parallels studies in sleep showing how the brain can locally “wake up” in order to process sensory information coming from the environment. Here, we show the opposite phenomenon and how sleep intrusions during wakefulness can make our minds wander somewhere or nowhere.”

The researchers note the need for future studies to more concretely establish this interpretation and are also exploring if this phenomenon of local sleep occurred more strongly in people suffering from attention deficit disorders like ADHD.