delanceyplace.com 2/22/10 - the brain's dark matter

In today's excerpt - the mind 'at rest' is often more active and at the least almost as active as the mind when it is engaged in a task:

"Many neuroscientists have long assumed that much of the neural activity inside your head when at rest matches your subdued, somnolent mood. In this view, the activity in the resting brain represents nothing more than random noise, akin to the snowy pattern on the television screen when a station is not broadcasting. ... But recent analysis produced by neuroimaging technologies has revealed something quite remarkable: a great deal of meaningful activity is occurring in the brain when a person is sitting back and doing nothing at all.

"It turns out that when your mind is at rest—when you are daydreaming quietly in a chair, say, [or] asleep in a bed or anesthetized for surgery—dispersed brain areas are chattering away to one another. And the energy consumed by this ever active messaging known as the brain's default mode, is about 20 times that used by the brain when it responds consciously to an outside stimulus. Indeed, most things we do consciously, be it sitting down to eat dinner or making a speech, mark a departure from the baseline activity of the brain default mode. ...

"Further analyses indicated that performing a particular task increases the brain's energy consumption by less than 5 percent of the underlying baseline activity. A large fraction of the overall activity—from 60 to 80 percent of all energy used by the brain—occurs in circuits unrelated to any external event. With a nod to our astronomer colleagues, our group came to call this intrinsic activity the brain's dark energy a reference to the unseen energy that also represents the mass of most of the universe. ...

"In the mid-1990s, we noticed quite by accident that surprisingly certain brain regions experienced a decreased level of activity from the baseline resting state when subjects carried out some task. These areas—in particular a section of the medial parietal cortex (a region near the middle of the brain involved with remembering personal events in one's life among other things)—registered this drop when other areas were engaged in carrying out a defined task such as reading aloud. Befuddled, we labeled the area showing the most depression MMPA for 'medial mystery parietal area.'

"A series of experiments then confirmed that the brain is far from idling when not engaged in a conscious activity. In fact, the MMPA as well as most other areas remains constantly active until the brain focuses on some novel task at which time some areas of intrinsic activity decrease. At first our studies met with some skepticism. In 1998, we even had a paper on such findings, rejected because one referee suggested that the reported decrease in activity was an error in our data. The circuits the reviewer asserted were actually being switched on at rest and switched off during the task. Other researchers, however, reproduced our results for both the medial parietal cortex—and the medial prefrontal cortex (involved with imagining what other people are thinking as well as aspects of our emotional state). Both areas are now considered major hubs of the brain's default mode network."


author:

Marcus E. Raichle

title:

The Brain's Dark Energy

publisher:

Scientific American

date:

March 2010

pages:

44-47
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