After finishing his PhD in neuroscience in 2016, Thomas Andrillon spent a year road-tripping around Africa and South America with his wife. One evening, on a particularly difficult road in Patagonia, his mind began to wander and he ended up accidentally flipping the car. Luckily, no one was hurt. As locals rushed in to help, they asked Andrillon what had happened. Was there an animal on the road? Had he fallen asleep at the wheel? “I had difficulty explaining that I was just thinking about something else,” he remembers. 

This experience made him think. What had happened? What was going on in his brain when his mind began to wander? 

In 2017, Andrillon started his postdoctoral research with neuroscientists Naotsugu Tsuchiya and Joel Pearson at Monash University in Melbourne. Shortly after, Tsuchiya and Andrillon teamed up with philosopher Jennifer Windt, also at Monash, to dive into the neural basis of mind wandering.

Initially, Andrillon says, they wanted to know if they could detect mind wandering from facial expressions, recalling how teachers claim to be very good at knowing when their students are not paying attention. So they did a pilot experiment in which they filmed their test subjects performing a tedious, repetitive task. 

There are many ways of not paying attention.

—Thomas Andrillon, Paris Brain Institute

After reviewing the videos, one of Andrillon’s students came to him, concerned. “I think we have a problem,” said the student. “[The subjects] look exhausted.” Sure enough, even though all the study participants were awake, they were obviously struggling to not fall asleep, says Andrillon. It was this observation that gave them the idea to broaden their focus, and start looking at the connection between wavering attention and sleep. 

“There are many ways of not paying attention,” Andrillon says, so it was important for the group to focus on two distinct types: mind wandering (thinking about something unrelated to the task at hand) and mind blanking (not thinking about anything). 

The researchers used a similar approach to their pilot experiment, but instead of monitoring the subjects with video cameras, they used an electroencephalogram (EEG) to measure brain activity. All 63 electrodes had to be individually placed on each participant’s head—Andrillon jokes that this part of the experiment was more like going to a hairdresser than participating in a scientific study. 

After being hooked up to the EEG, participants took part in a classical psychological experiment called a sustained attention to response task (SART). Sitting in front of a screen with flashing digits, the participants were instructed to hit a button every time they saw a number—except when they saw the number three, in which case they were supposed to just wait until another number flashed on the screen. “It’s a fairly boring task,” says Andrillon, “and that’s on purpose. It allows people to think about other things.” 

For a total of about an hour and a half, spread over several sessions, the participants were occupied with the SART test, but with one additional twist: Every minute or so, a computer message would pop up to interrupt the subject and ask them to rate their level of awareness as “on task,” “mind wandering,” or “mind blanking.”  They were also asked where they fell on a spectrum of “extremely tired” to “extremely alert.”

Perhaps not surprisingly, the team found that when a subject reported being “on task,” they tended to perform better on the SART test. Mind wandering was associated with more false alarms (pressing the button when they weren’t supposed to), while mind blanking was associated with more misses (not pressing the button when they were supposed to). 

Andrillon says the researchers expected a blanking brain to resemble a sleepy one, and a wandering mind to have characteristics of hyperarousal and impulsivity. So they were surprised when the EEG data revealed that during both mind blanking and mind wandering, high-amplitude slow waves emerge, similar to the ones that appear during the transition from waking to sleep. 


The difference between the two forms of inattention came down to where in the brain the waves were located. During mind wandering, slow waves emanated from the front of the brain, whereas during mind blanking the waves appeared in both the front and the back. Essentially, the researchers say, mind wandering and mind blanking seem to be instances of “local sleep”—when some parts of the brain are asleep while other areas remain awake. They published their findings in Nature Communications in July. 

University of California, Santa Barbara, psychological science researcher Jonathan Schooler says that getting a scientific handle on mind wandering can be challenging. “Mind wandering is an intrinsically private experience,” he explains. Schooler, who was not involved in the study, says the paper effectively triangulates on what is happening physiologically during mind wandering by integrating the EEG data with the self-reporting from study subjects and behavioral performance measures. “Each one shores up the other in helping you to really understand the phenomena.”

Rebecca Spencer, a neuroscientist and sleep researcher at the University of Massachusetts Amherst who was not involved in the study, says that it’s interesting how clearly the researchers were able to detect the pure slow waves, as her group has had a hard time detecting slow waves in older adults even during sleep. “It’s pretty impressive that you can get those slow waves in a waking person given that in some sleeping people they’re hard to find,” she says.

Spencer wonders how generalizable this phenomenon is across different tasks. Although the SART tests used in the paper are pretty standard in the field, Spencer says she doesn’t know if they’re the best representation of real-life situations in which mind blanking and mind wandering tend to set in. “Why don’t they study a writer?” she laughs. “How similar is [the SART test] to getting writer’s block or the things that we’re actually doing with our day?” 

In a similar vein, Windt notes that mind blanking and mind wandering can be particularly difficult to study because an experimenter can’t directly induce either phenomenon. “What you can basically do,” she says, “is confront people with different types of tasks—often boring and tedious tasks—and hope that performing these tasks will actually induce mind wandering.”

Moving forward, Andrillon, who is now a research fellow at the Paris Brain Institute, says he and his colleagues are looking at ways to harness their findings for the clinic. In particular, he notes that children and adults with attention-deficit/hyperactivity disorder (ADHD) report high rates of sleep disturbances compared to the general population. Andrillon says he wants to investigate whether there is a link between poor sleep and the attention deficits that many people with ADHD experience. 

Although the effects of mind wandering can range from embarrassing (getting called on when you aren’t paying attention) to dangerous (running your car off the road), there may be some situations in which this local sleep could be beneficial. 

“There are a lot of situations and kinds of tasks that we engage in that really demand our ongoing attention,” says Windt, “and for those types of things, mind wandering does indeed seem to be quite detrimental in many cases.” But, she adds, new research is revealing that, when appropriate, mind wandering isn’t all bad. It can make tedious tasks more enjoyable, she says, and may even give people opportunities to think more creatively. 

In fact, Andrillon says he’s had several important insights and ideas related to this project while in a car—although he assures The Scientist that the mind wandering never again occurred to the extent that he wasn’t paying attention to the road. 

Andrillon remembers trying to assure onlookers that the crash in Patagonia had nothing to do with sleep. “Ironically, after doing this research, it could very well be that part of my brain was actually sleeping.”