Background Attention deficit/hyperactivity disorder (ADHD) is a major public health concern. It has been suggested that the brain’s default network may provide a crucial avenue for understanding the neurobiology of ADHD. Evaluations of the default network have increased over recent years with the applied technique of resting-state functional connectivity MRI (rs-fcMRI). These investigations have established that spontaneous activity in this network is highly correlated at rest in young adult populations. This coherence seems to be reduced in adults with ADHD. This is an intriguing finding, as coherence in spontaneous activity within the default network strengthens with age. Thus, the pathophysiology of ADHD might include delayed or disrupted maturation of the default network. If so, it is important to determine whether an altered developmental picture can be detected using rs-fcMRI in children with ADHD. Methods The present study utilized the typical developmental context provided previously by Fair et al (1) to examine coherence of brain activity within the default network using rs-fcMRI in children with (n=23) and without ADHD (n=23). Results We found that functional connections previously shown as developmentally dynamic in the default network were atypical in children with ADHD - consistent with perturbation or failure of the maturational processes. Conclusions These findings are consistent with the hypothesis that atypical consolidation of this network over development plays a role in ADHD.

Despite growing interest in conceptualizing ADHD as involving disrupted emotion regulation, few studies have examined the physiological mechanisms related to emotion regulation in children with this disorder. This study examined parasympathetic and sympathetic nervous system reactivity via measures of respiratory sinus arrhythmia (RSA) and cardiac pre-ejection period (PEP) in children with ADHD (n=32) and typically developing controls (n=34), using a novel emotion task with four conditions: negative induction, negative suppression, positive induction, and positive suppression of affect. Both groups showed strong task-response effects in RSA. However, typically developing children showed systematic variation in parasympathetic activity (RSA) depending on both emotion valence (more activation for negative emotion, reduced activation for positive emotion) and task demand (more activation for suppression than induction). In contrast, children with ADHD displayed a stable pattern of elevated parasympathetic activity (RSA) across all task conditions compared to baseline. No group differences in sympathetic activity (PEP) were observed. It is concluded ADHD in childhood is associated with abnormal parasympathetic mechanisms involved in emotion regulation.

Objective Identification of biomarkers is a priority for attention deficit/hyperactivity disorder (ADHD). Studies have documented macrostructural brain alterations in ADHD, but few have examined white matter microstructure, particularly in pre-adolescent children. Given dramatic white matter maturation across childhood, microstructural differences seen in adolescents and adults with ADHD may reflect compensatory restructuring, rather than early neurophenotypic markers of the disorder. Method Using Tract-Based Spatial Statistics, mean fractional anisotropy (FA) maps were created using diffusion tensor imaging. FA and mean diffusivity (MD), and associated axial and radial diffusivity, were compared between 16 children with ADHD and 20 healthy children (age 7-9 years). Results ADHD youth showed reduced FA in fronto-parietal, fronto-limbic, cerebellar, corona radiata and temporo-occipital white matter compared to controls. In addition, ADHD was associated with lower MD in the posterior limb of the internal capsule and fronto-parietal white matter, and greater MD in fronto-limbic white matter. Lower axial diffusion and/or higher radial diffusion were differentially observed for ADHD youth in earlier versus later maturing areas of group FA/MD difference. Conclusions This study suggests that, even prior to adolescence, ADHD represents a disorder of altered structural connectivity of the brain, characterized by distributed atypical white matter microstructure. Additionally, later maturing fronto-limbic pathways also were abnormal in children with ADHD, likely due to delayed or reduced myelination, a finding not previously demonstrated in the adolescent or adult stages of the disorder. These results suggest that disruptions in white matter microstructure may play a key role in the early pathophysiology of ADHD.

Background A key underlying process that may contribute to attention-deficit/hyperactivity disorder (ADHD) involves alterations in reward evaluation, including assessing the relative value of immediate over delayed rewards. This study examines whether children with ADHD discount the value of delayed rewards to a greater degree than typically developing children using a delay discounting task. Methods Children aged 7–9 years diagnosed with ADHD and controls completed a task in which they chose between a hypothetical $10 available after a delay (7, 30, 90 and 180 days) versus various amounts available immediately. Results ADHD participants discounted more steeply than controls. However, this effect did not survive covarying of IQ. Conclusions ADHD is associated with a steeper delay gradient when contemplating hypothetical later rewards, but not independently of IQ. The interplay of cognitive processing and IQ with reward evaluation in ADHD requires further exploration.

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