One moment you're paying close attention to a lecture, the next you're making a mental list of items you need to pick up at the store and wondering who will be at the party on Saturday night. Minds wander, and now a study sheds new light on what happens in the brain when thoughts go astray.
The researchers, led by cognitive psychologist Malia Mason, currently a postdoctoral fellow at Harvard Medical School in Boston, began by asking 19 volunteers to perform simple recall tasks such as memorizing a short string of letters and reproducing them in forward or reverse order. Reasoning that minds wander more when the job at hand isn't very demanding, the researchers had the volunteers practice the tasks for 30 minutes on three consecutive days. During a fourth practice session, the researchers butted in to ask the subjects whether they were having stray thoughts. As expected, they reported more random thoughts when working on a familiar sequences than when grappling with a novel one.
On the fifth day of the experiment, volunteers slid into a functional magnetic resonance imaging (fMRI) scanner. The scans revealed that a particular set of interconnected brain regions was more active when volunteers worked on well-practiced sequences and in individuals who'd reported a greater tendency for mental wandering. Mason and colleagues report their findings in the 19 January issue of Science.
In 2001, neurologist Marcus Raichle of Washington University in St. Louis, Missouri, and colleagues noted that the same set of brain regions buzzes with activity when people aren't concentrating on any particular task. Raichle called it the "default network." He says that the new work suggests that activity in the default network is necessary to generate spontaneous thoughts and adds to evidence that it makes an important contribution to our inner life. In one published case study, Raichle notes, a woman who suffered damage to part of the default network initiated almost no spontaneous thoughts. "Her mind was empty," Raichle says.
The study leaves open the question of why minds wander, says Jonathan Schooler, a psychologist at the University of British Columbia in Vancouver, Canada. Schooler suspects that mental rambling is generally beneficial. "A lot of the time, people are thinking about worries or problems that they need to work out," Schooler says, adding that creative insights often happen during these episodes. The new study could be a big help to researchers if it leads to a way to use fMRI to detect mind wandering without interrupting an experimental subject, Schooler says.