The authors performed a comprehensive meta-analysis of task-based functional MRI studies
of attention deficit hyperactivity disorder (ADHD).
The authors searched PubMed, Ovid, EMBASE, Web of Science, ERIC, CINAHAL, and NeuroSynth
for studies published through June 30, 2011. Significant differences in brain region
activation between individuals with ADHD and comparison subjects were detected using
activation likelihood estimation meta-analysis. Dysfunctional regions in ADHD were
related to seven reference neuronal systems. The authors performed a set of meta-analyses
focused on age groups (children and adults), clinical characteristics (history of
stimulant treatment and presence of psychiatric comorbidities), and specific neuropsychological
tasks (inhibition, working memory, and vigilance/attention).
Fifty-five studies were included (39 for children and 16 for adults). In children,
hypoactivation in ADHD relative to comparison subjects was observed mostly in systems
involved in executive function (frontoparietal network) and attention (ventral attentional
network). Significant hyperactivation in ADHD relative to comparison subjects was
observed predominantly in the default, ventral attention, and somatomotor networks.
In adults, ADHD-related hypoactivation was predominant in the frontoparietal system,
while ADHD-related hyperactivation was present in the visual, dorsal attention, and
default networks. Significant ADHD-related dysfunction largely reflected task features
and was detected even in the absence of comorbid mental disorders or a history of
stimulant treatment.
A growing literature provides evidence of ADHD-related dysfunction in multiple neuronal
systems involved in higher-level cognitive functions but also in sensorimotor processes,
including the visual system, and in the default network. This meta-analytic evidence
extends early models of ADHD pathophysiology that were focused on prefrontal-striatal
circuits.