Anterior cingulate cortex dysfunction in attention-deficit/hyperactivity disorder revealed by fMRI and the counting stroop

Background: The anterior cingulate cognitive division (ACcd) plays a centra l role in attentional processing by: 1) modulating stimulus selection (i.e, , focusing attention) and/or 2) mediating response selection. We hypothesiz ed that ACcd dysfunction might therefore contribute to producing core featu res of attention-defcit/hyperactivity disorder (ADHD), namely inattention a nd impulsivity. ADHD subjects have indeed shown performance deficits on the Color Stroop, an attentional/cognitive interference task known to recuit. the ACcd. Recently, the Counting Stroop, a Stroop-variant specialized for f unctional magnetic resonance imaging (fMRI), produced ACcd activation in he althy adults. In the present fMRI study, the Counting Stroop was used to ex amine the functional integrity of the ACcd in ADHD. Methods: Sixteen unmedicated adults from two groups (8 with ADHD and 8 matc hed control subjects) performed the Counting Stroop during fMRI Results: While both groups showed an interference effect, the ADHD group, i n contrast to control subjects, failed to activate the ACcd during the Coun ting Stroop. Direct comparisons showed ACcd activity was significantly high er in the control group. ADHD subjects did activate a frontostriatal-insula r network indicating ACcd hypoactivity was not caused by globally poor nehr ronal responsiveness, Conclusions: The data support a hypothesized dysfunction of the ACcd in ADH D.