Failing to deactivate: resting functional abnormalities in autism

Abstract

Several regions of the brain (including medial prefrontal cortex, rostral anterior cingulate, posterior cingulate, and precuneus) are known to have high metabolic activity during rest, which is suppressed during cognitively demanding tasks. With functional magnetic resonance imaging (fMRI), this suppression of activity is observed as "deactivations," which are thought to be indicative of an interruption of the mental activity that persists during rest. Thus, measuring deactivation provides a means by which rest-associated functional activity can be quantitatively examined. Applying this approach to autism, we 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. We 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.

Fig. 1.

Significant functional activity derived from group whole-brain analyses (P < 0.01, cluster corrected). t values are displayed, with negative t values representing deactivations. The black outlines correspond to the area of deactivation derived from the number vs. rest condition in controls (A Left) mapped onto the sagittal slices of the images shown. These outlines, which represent regions active during rest, highlight the presence or absence of activations or deactivations in each image. Each sagittal slice location differs slightly because each image was chosen to best represent the midline activity for each group and comparison. The comparisons shown are number vs. rest (A), neutral vs. rest (B), emotional vs. rest (C), and emotional vs. neutral (D).

Fig. 2.

Correlation between functional activity in a ventral MPFC cluster (Inset) and score on the social subscale of the Autism Diagnostic Interview–Revised in the ASD group.