THURSDAY, Jan. 18, 2007 (HealthDay News) -- Flitting from one thought to the next, the brain at rest seems random and scattered. But new brain-imaging research suggests the "wandering" mind may have purpose, too.
"This type of thought could be a sort of 'default' state of the mind, a psychological baseline," said study lead author Dr. Malia Mason, a postdoctoral fellow at Massachusetts General Hospital's Martinos Center for Biomedical Imaging, in Boston.
In that sense, she said, idle daydreaming could be an "optimal state of arousal" the brain requires to stayed primed for more purposeful tasks -- much like an idling car waits to be shifted into gear.
That remains a theory, but the study, published in the Jan. 19 issue of the journal Science, did find a distinct pattern of brain regions lighting up whenever the mind began to wander.
In its study, Mason's group used high-tech functional MRI (fMRI) to compare the brain activity of healthy young adults as they performed mentally taxing tasks or gave their minds over to random thoughts.
According to the researchers, a distinct, complex network of disparate brain regions clicked into gear when people were simply letting their minds wander.
"It involved a number of areas," Mason said. "Regions like the medial prefrontal cortex [in the forebrain]," she said, "but also areas like the medial parietal cortices," located closer to the back of the brain.
It's not yet clear why these areas might be necessary for ruminative thought, or what role any one region might play. "My guess is that each region has its own unique function, because there'd be no need for a network at all, if all of these regions were doing the same thing," Mason said.
One expert applauded the Boston researchers' efforts.
"This is one of the few experiments that have tried to scientifically and empirically examine something that's notoriously difficult to study," said Daniel Kennedy, a postgraduate student in the department of neuroscience at the University of California, San Diego.
Kennedy led a study, published last May in the Proceedings of the National Academy of Sciences, that found that autistic individuals do not show fMRI evidence of daydreaming in the way that non-autistic people do.
According to Kennedy, the vast majority of brain science has focused on people actively engaged in particular tasks or specific emotional states. But, in reality, most people spend a large part of their waking life in mundane pursuits that leave the mind free to wander, something neuroscientists call "stimulus-independent thought."
"The functioning of all that is still pretty mysterious," Kennedy said.
Even more mysterious is why humans might have evolved a "default" mode of random brain activity at all.
Numerous theories abound, Mason said, none of them proven. One is the "optimal arousal state" she described above. "Everyone might have an optimal arousal state that they need to have internally, to be able to readily respond to the external world," she said.
"For example, I can sit at a restaurant and have dinner, but simultaneously be aware of where I was before and where I'm going next," Mason noted. "That happens, I think, through this extra thought. It gives you a sense of coherence between your past and future, along with a sense of self."
Then there's a curious mental phenomenon Mason calls "incubation."
"You know when you try and remember something, and you just can't get it, but then a few hours later, it spontaneously comes to you?" Mason said. She noted that one theory holds that the so-called "idle" mind has actually been working away behind the scenes, gnawing away at life's little puzzles and "incubating" the answer.
Maybe, she said, "there's been something going on in the background, a covert search that you don't have an awareness of."
All of this is just more food for thought, random or otherwise, Mason said. "A lot of this stuff, we just don't know."
More information
There's more on how the brain works at Harvard University.
