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1.
Neuroimage. 2007 Oct 1;37(4):1083-90; discussion 1097-9. Epub 2007 Mar 6.

A default mode of brain function: a brief history of an evolving idea.

Author information

1
Department of Radiology, Washington University School of Medicine, St Louis, MO 63110, USA. marc@npg.wustl.edu

Abstract

The concept of a default mode of brain function arose out of a focused need to explain the appearance of activity decreases in functional neuroimaging data when the control state was passive visual fixation or eyes closed resting. The problem was particularly compelling because these activity decreases were remarkably consistent across a wide variety of task conditions. Using PET, we determined that these activity decreases did not arise from activations in the resting state. Hence, their presence implied the existence of a default mode. While the unique constellation of brain areas provoking this analysis has come to be known as the default system, all areas of the brain have a high level of organized default functional activity. Most critically, this work has called attention to the importance of intrinsic functional activity in assessing brain behavior relationships.

[Indexed for MEDLINE]
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2.
Proc Natl Acad Sci U S A. 2001 Mar 27;98(7):4259-64. Epub 2001 Mar 20.

Medial prefrontal cortex and self-referential mental activity: relation to a default mode of brain function.

Author information

1
Mallinckrodt Institute of Radiology and Department of Psychiatry, Washington University School of Medicine, St. Louis, MO 63110, USA. gusnard@npg.wustl.edu

Abstract

Medial prefrontal cortex (MPFC) is among those brain regions having the highest baseline metabolic activity at rest and one that exhibits decreases from this baseline across a wide variety of goal-directed behaviors in functional imaging studies. This high metabolic rate and this behavior suggest the existence of an organized mode of default brain function, elements of which may be either attenuated or enhanced. Extant data suggest that these MPFC regions may contribute to the neural instantiation of aspects of the multifaceted "self." We explore this important concept by targeting and manipulating elements of MPFC default state activity. In this functional magnetic resonance imaging (fMRI) study, subjects made two judgments, one self-referential, the other not, in response to affectively normed pictures: pleasant vs. unpleasant (an internally cued condition, ICC) and indoors vs. outdoors (an externally cued condition, ECC). The ICC was preferentially associated with activity increases along the dorsal MPFC. These increases were accompanied by decreases in both active task conditions in ventral MPFC. These results support the view that dorsal and ventral MPFC are differentially influenced by attentiondemanding tasks and explicitly self-referential tasks. The presence of self-referential mental activity appears to be associated with increases from the baseline in dorsal MPFC. Reductions in ventral MPFC occurred consistent with the fact that attention-demanding tasks attenuate emotional processing. We posit that both self-referential mental activity and emotional processing represent elements of the default state as represented by activity in MPFC. We suggest that a useful way to explore the neurobiology of the self is to explore the nature of default state activity.

PMID:
11259662
PMCID:
PMC31213
DOI:
10.1073/pnas.071043098
[Indexed for MEDLINE]
Free PMC Article
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3.
Proc Natl Acad Sci U S A. 2001 Jan 16;98(2):676-82.

A default mode of brain function.

Author information

1
Mallinckrodt Institute of Radiology and Departments of Neurology and Psychiatry, Washington University School of Medicine, St. Louis, MO 63110, USA. marc@npg.wustl.edu

Abstract

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.

PMID:
11209064
PMCID:
PMC14647
DOI:
10.1073/pnas.98.2.676
[Indexed for MEDLINE]
Free PMC Article
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