Neural mechanisms of interference control and time discrimination in attention-deficit/hyperactivity disorder.

OBJECTIVE Both executive functions and time perception are typically impaired in subjects with attention-deficit/hyperactivity disorder (ADHD). However, the exact neural mechanisms underlying these deficits remain to be investigated. METHOD Fourteen subjects with ADHD and 14 age- and IQ-matched controls (aged 9 through 15 years) were assessed with functional magnetic resonance imaging while they performed a combined spatial stimulus-response compatibility (SRC) and time duration discrimination (TD) paradigm using identical stimuli for all experimental conditions. RESULTS Children with ADHD performed less accurately in the SRC but not in the TD task compared with controls. On the brain level, subjects with ADHD showed significantly reduced neural activity in the left putamen during SRC and reduced fronto-cerebellar activation during TD when compared with the baseline conditions. Compared with subjects with ADHD, control subjects had increased activation in a left-hemispheric fronto-parietal network during the SRC task and in the right superior-frontal gyrus during the TD task. Functional connectivity analyses revealed abnormal fronto-parietal coupling during the SRC task and reduced fronto-cerebellar connectivity during the TD task in the ADHD group compared with controls. CONCLUSIONS Our findings suggest specific but distinct patterns of cerebral dysfunction associated with interference control and TD processing in ADHD, characterized by both reduced neural activation in regions critical for task performance and reduced co-activation of frontal cortex. Group differences on the behavioral level were controlled by several methodological approaches. Nonetheless, given the use of a block design, we cannot rule out the possibility that between-group differences in behavior confounded the neural activation patterns.