Inaugural Article
Neurobiology
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
* Mallinckrodt Institute of Radiology and Departments of
Neurology and § Psychiatry, Washington
University School of Medicine, St. Louis, MO 63110
Contributed by Marcus E. Raichle, October 26, 2000
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. Many
suspect that left unconstrained, its activity will vary unpredictably.
Despite this prediction we identify a baseline state of the normal
adult human brain in terms of the brain oxygen extraction fraction or
OEF. The OEF is defined as the ratio of oxygen used by the brain to
oxygen delivered by flowing blood and is remarkably uniform in the
awake but resting state (e.g., lying quietly with eyes closed). Local
deviations in the OEF represent the physiological basis of signals of
changes in neuronal activity obtained with functional MRI during a wide
variety of human behaviors. We used quantitative metabolic and
circulatory measurements from positron-emission tomography to obtain
the OEF regionally throughout the brain. Areas of activation were
conspicuous by their absence. All significant deviations from the mean
hemisphere OEF were increases, signifying deactivations, and resided
almost exclusively in the visual system. Defining the baseline state of
an area in this manner attaches meaning to a group of areas that
consistently exhibit decreases from this baseline, during a wide
variety of goal-directed behaviors monitored with positron-emission tomography and functional MRI. These decreases suggest the existence of
an organized, baseline default mode of brain function that is suspended
during specific goal-directed behaviors.
To whom reprint requests should be addressed at:
Washington University School of Medicine, 4525 Scott Avenue, Room 2116, St. Louis, MO 63110. E-mail: marc{at}npg.wustl.edu.
