What causes our mind to blank out or wander? It’s the ‘local sleep’ in brains, study suggests

Study analysed differences in behaviour when mind is blanking with no activity or wandering with high activity, & correlated responses with regions where slow brain waves occurred.

Representational image | Photo: Pixabay

Bengaluru: A new study on people performing a set of boring tasks has revealed the mechanisms under which the mind starts to wander and blank out, what the nature of consequences of those lapses in attention could be, and how they are triggered.

The researchers identify localised slow waves — patterns of brain activity similar to when we are about to fall asleep — occurring in the front and back parts of the brain. The team says identifying the location of these slow waves in the brain could distinguish between sluggish and impulsive behaviours.

The waves can also help make the distinction between the mind wandering, with high brain activity, and the mind blanking, with no brain activity.

The authors conclude that attention lapses share a common origin in the brain, which is the emergence of local, sleep-like brain waves within an awake brain. These waves acts like a “functional switch”, affecting the brain network activity at that point.

Depending on the location where they occur, they could lead to different responses. The phenomenon is called local sleep, and the authors state that this occurs not just when the brain is pushed to an extreme state of sleep deprivation, but also in well-rested individuals.

The findings were published in the journal Nature this week.

Brain waves

The human brain directs cognitive resources towards amplification of information relevant to a specific behavioural goal when we focus on a task at hand. But this attention can also be reoriented inwards, which we commonly refer to as loss of focus or mind wandering.

Our stream of thoughts can also pause when the mind blanks out and loses attention.

When our brain wanders, there is “rich and spontaneous” mental activity, whereas when our mind blanks, there is an absence of mental activity.

A defining trait of attention is its fleeting nature, state the researchers, and the difficulty humans and other animals have to maintain it on a task. Mind blanking and mind wandering often occurs without our knowledge or even will.

These occur due to voluntary or involuntary attention lapses, and their consequences can vary. Lapses in attention can lead to a lack of responsiveness or reactions that are sluggish and slow. But they can also result in impulsive and wrong or unnecessary responses.

Mind blanking, mind wandering, sluggish responses, and impulsive responses, are all also observed in people with sleep deprivation. Previous studies have shown that attention lapses increase as fatigue increases, and that both mind wandering and mind blanking occur during times between wakefulness and sleep.

As fatigue and sleep deprivation increase, the sleep-like slow waves start occurring in localised regions, leading to a phenomenon called local sleep. An increase in these waves can affect daily brain functions and cause attention lapses. Studies have also shown that increase in these waves lead to an increase in errors in tasks.

Study design

The study was small, with only 26 participants who were healthy. They were asked to perform mentally “undemanding” tasks like watching the screen and responding to ‘Go/NoGo’ signals.

Their brain activity was monitored using high-density electroencephalography, with 63 electrodes connected all over their scalps. Their pupil dilation was also measured as a marker of vigilance.

The participants were not in a state of sleep deprivation, and were not in environments conducive to falling asleep or dozing off, such as being reclined.

They were often interrupted by the researchers and asked about whether they had been focussing on the task, or were thinking about something else (mind wandering), or were thinking about nothing (mind blanking).

At the end of this experiment, participants reported focussing only about half the time. The rest of the time, their minds were blanking or wandering. The authors also monitored the behavioral patterns before the onset of mind wandering or blanking activities.

The findings from the experiment showed that both mind blanking and wandering decrease performance. Whenever the participants failed to stay on the task, they also reported feeling more tired.

The findings

Mind blanking led the participants to more misses and slower response times, leading to a sluggish mental state. Mind wandering too induced more misses, but the response time of all participants was much faster, which the authors say back the idea that it leads to impulsive mental states.

The authors also found that during both mind blanking and wandering, the participants were in a state of lower vigilance, with significantly smaller pupils. But the pupil size did not vary between the two kinds of brain activity. Lowered vigilance and low pupil dilation was also correlated with an increase in brain wave amplitudes, leading to an increased level of slow waves.

The authors also noted that the location of where these slow waves occurred influenced responses. When they occurred in the electrodes at the front of the brain, participants were prone to responding faster and were more likely to have their mind wandering. Slow waves occurring at the back electrodes resulted in sluggish responses.

It seems therefore that posterior slow waves (leading to MB) could be a more global local sleep event, involving more cortical regions, which is also reflected in performance or vigilance ratings.
13/n pic.twitter.com/lJbiG0qhjW

— Thomas Andrillon (@thandrillon) June 29, 2021

Mind wandering or slow waves in the front part of the brain also led to more false alarms, or accidentally clicking when the participant shouldn’t. Mind blanking or slow waves at the back led to more misses by not clicking when participant should.

This is caused by a change in how participants evaluated incoming informational evidence, with front waves accumulating evidence slower for NoGo signals, and back waves slower for ‘Go’ signals leading to slow response times.

The findings show a spatial and temporal relationship between local sleep and behavioral errors as measured by slow waves.