The Human Brain During Condition White
-- Daydreaming seems to be the default setting of the human mind and certain brain regions are devoted to it, U.S. researchers reported Friday.
When people are given a specific task to do, they focus on that task but then other brain regions get busy during down time, the researchers report in Friday's issue of the journal Science.
"There is this network of regions that always seems to be active when you don't give people something to do," psychologist Malia Mason of Harvard Medical School and Massachusetts General Hospital said in a telephone interview.
When Mason asked people what was happening during this down time, the answer was clear.
"It's daydreaming," she said. "But I find that the vast majority of time, people aren't having fanciful thoughts. People are thinking about what they have to do later today."
Her team has chosen to call it stimulus-independent thought or mind wandering.
Neurologists and psychologists have debated what goes on when people are not specifically thinking about or doing something, and there had been general agreement that the mind does not simply go blank.
Mason's team set up an experiment using the relatively new technology of functional magnetic resonance imaging or fMRI to see what is going on.
FMRI allows scientists to take real-time images of the brain, showing which areas are active and when. They can do this while talking to the person being imaged, so they can see the effects of an activity as it happens.
Mason's team recruited 19 volunteers and scanned them as they did a variety of tasks. "The verbal working memory task involved remembering and manipulating four four-letter sequences (e.g., 'R H V X')," they wrote.
The volunteers were also imaged when they were sitting there, waiting between tasks.
Wandering and flitting
"In the absence of a task that requires deliberative processing, the mind generally tends to wander, flitting from one thought to the next with fluidity and ease," the researchers wrote.
Now they know what that looks like.
Active regions include the superior frontal gyrus, which is one of the main bumps on the front part of the human brain, the insula, which is on the side of the brain, and parts of the temporal lobe, at the back of the brain.
Mason is not sure why this activity occurs, but believes it underlies some of the basic mind functions that define people -- although her team has not imaged any animals.
One possibility, her team said, is that the brain always does something so that it is in an active state when quick thoughts or reactions are needed.
"A second possibility is that as a kind of spontaneous mental time travel (stimulus-independent thought) lends a sense of coherence to one's past, present, and future experiences," the researchers wrote.
"We are not stuck in the here and now. We can be stuck in our car in traffic and we are not (mentally) stuck there," Mason added.
Or there could be no reason at all for daydreaming.
"Although the thoughts the mind produces when wandering are at times useful, such instances do not prove that the mind wanders because these thoughts are adaptive; on the contrary the mind may wander simply because it can," they concluded.