Kennedy et al report interesting functional magnetic resonance imaging (fMRI) data on normal compared with autistic brains. From their article:
Internally directed processes, such as self-reflective thought and most higher-order social and emotional processes, consistently activate a medial cortical network involving several brain regions, namely, the medial prefrontal cortex (MPFC) and adjacent rostral anterior cingulate cortex (rACC), posterior cingulate cortex (PCC), and precuneus (PrC). Interestingly, this network is active when normal subjects are passively resting, leading many to speculate that these internally directed thoughts dominate the resting state. Self-reports from subjects while at rest further support this interpretation, wherein they typically describe "autobiographical reminiscences, either recent or ancient, consisting of familiar faces, scenes, dialogues, stories, and melodies". Conversely, activity in this midline "resting network" is reduced when subjects perform externally directed, attention-demanding, goal-oriented tasks (such as the Stroop task or math calculations), and the resulting "deactivation" of this network is thought to be an indicator of an interruption of ongoing internally directed thought processes. Thus, measuring deactivation provides a means by which rest-associated functional activity can be quantitatively examined.
Applying this approach to autism, Kennedy et al found that the autism group failed to demonstrate this deactivation effect. Furthermore, there was a strong correlation between a clinical measure of social impairment and functional activity within the ventral medial prefrontal cortex. They speculate that the lack of deactivation in the autism group is indicative of abnormal internally directed processes at rest, which may be an important contribution to the social and emotional deficits of autism.