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Complexity Digest 2001.18 - 08
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30-Apr-2001

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A Default Mode of Brain	 Function, Proc. Natl. Acad. Sci.
 









In PET ( Positron Emission Technology) of fMRI
(functional Magnetic Resonance) task induced increase in regional
brain activity during specific goal-orientated behavior are
commonly observed by comparing between a specific experimental
task and a control task. The difference between the two is
considered to represent the brain activity that is associated with
the process of interest. Task induced decreases in regional
activity has also been observed even when the control task
consists of lying quietly. But what does the resting brain
activity represent? In the following paper a theory on 'baseline'
state of the brain is proposed.

The authors have used PET to measure a variety of metabolic and
circulation relationship between blood flow and oxygen consumption
in the brain. They have formulated 'oxygen extraction factor'
[OEF] that is the fraction of oxygen available to the
brain to that used by the brain and cerebral blood flow
[CBF] . Through measuring OEF, the authors propose to
define the baseline state of the brain activity. OEF should
indicate which area is deactivated during resting state. The
deflection from the baseline state may be interpreted stimulus
processing in the brain. In support of their claim, experimental
data and images from subjects are given by the authors as 1) Maps
of the fraction of oxygen extracted by the brain from arterial
blood 2) Regions of the brain regularly observed to decrease their
activity.

Excerpts: A baseline or control state is fundamental to
the understanding of most complex systems. Defining a baseline
state in the human brain, arguably our most complex system, poses
a particular challenge. (…) All significant deviations from
the mean hemisphere OEF were increases, signifying deactivations,
and resided almost exclusively in the visual system. (…)
These decreases suggest the existence of an organized, baseline
default mode of brain function that is suspended during specific
goal-directed behaviors. 


	
A
  Default Mode of Brain
	Function, Marcus E.
	Raichle, Ann Mary MacLeod, Abraham Z. Snyder, William
  J. Powers, Debra A. Gusnard, and Gordon L. Shulman,
	Proc. Natl. Acad. Sci., USA, 98, 676-682 (2001),
	Contributed by Atin
  Das
 
 

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