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�…

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�…