Medial prefrontal cortex and self-referential mental activity: Relation toa default mode of brain function

Medial prefrontal cortex (MPFC) is among those brain regions having the hig hest baseline metabolic activity at rest and one that exhibits decreases fr om this baseline across a wide variety of goal-directed behaviors in functi onal imaging studies. This high metabolic rate and this behavior suggest th e existence of an organized mode of default brain function, elements of whi ch may be either attenuated or enhanced. Extant data suggest that these MPF C regions may contribute to the neural instantiation of aspects of the mult ifaceted "self." We explore this important concept by targeting and manipul ating elements of MPFC default state activity. In this functional magnetic resonance imaging (fMRI) study, subjects made two judgments, one self-refer ential, 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 accomp anied by decreases in both active task conditions in ventral MPFC. These re sults support the view that dorsal and ventral MPFC are differentially infl uenced by attention-demanding tasks and explicitly self-referential tasks. The presence of self-referential mental activity appears to be associated w ith 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 a nd emotional processing represent elements of the default state as represen ted by activity in MPFC. We suggest that a useful way to explore the neurob iology of the self is to explore the nature of default state activity.