Brain Appears to Have 'Daydreaming' Mode
Mon Dec 16, 5:28 PM ET Add Health - Reuters to My Yahoo!


By Alison McCook

NEW YORK (Reuters Health) - Much as a car's engine hums along even
when it's parked in neutral, the brain seems to contain a "default
mode" in which certain regions become more active at rest, US
researchers report.



"During rest, these regions appear to be interacting, because they
change at similar rates," lead author Dr. Michael D. Greicius of
Stanford University in California told Reuters Health.


Intriguingly, the behavior of these brain regions bears a certain
resemblance to what one would expect from brain areas that make up
human consciousness, Greicius added.


The default mode network supported in the current study generally
increases its activity when the brain is at rest, then drops in
activity once people are called to a certain task. In a similar way,
Greicius said, a person could be daydreaming or following a stream of
consciousness, but those activities would be zapped away as soon as
the person was called to action, perhaps by a ringing telephone.


In addition, some of the brain regions that may form parts of the so-
called default mode network have shown in previous studies to be
involved in certain aspects of consciousness, Greicius added. For
instance, one of the brain regions looked at in the current study,
the posterior cingulate cortex (PCC), has been shown to play a role
in the brain processes by which people recall memories. In addition,
PCC activity tends to peter out as people lose consciousness when
sedated.


Given that PCC forms a part of the theoretical default mode network,
Greicius and his colleagues suggest that this network may serve
similar functions, such as involving itself in remembering past
events, mulling over information, and thinking about the future.


Greicius cautioned in an interview, however, that the results of the
current study do not demonstrate that the default mode does, in fact,
represent the brain network involved in consciousness, nor is it
involved in any specific activity related to consciousness.


"All of this stuff is supportive, but none of it is definitive," he
said.


During the study, Greicius and his colleagues measured brain activity
in a handful of people during different activities: performing a
mental task, passively watching a pattern on a screen, or resting
with their eyes closed. They report their findings in the online
Early Edition of Proceedings of the National Academy of Sciences
(news - web sites).


The authors found that PCC and at least one other brain region known
as the ventral anterior cingulate cortex seem to show similar rates
of increase and decrease in activity in response to what people are
doing.


Greicius noted that the default mode regions continued to show high
activity while people passively watched the screen pattern--a finding
that makes sense, he said, for just because you are looking at
something, doesn't mean you can't daydream.


The current findings also demonstrate that the brain may need to be
active even when the mind is at rest, he added. "When the car is
running, the engine is still purring," Greicius said.


SOURCE: Proceedings of the National Academy of Sciences
2002;10.1073/pnas.0135058100.


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