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."
