Background-Because of its dense connections to the prefrontal cortex and basal ganglia, the cerebellum is thought to play an important role in cognition. Numerous MRI studies have found abnormalities in the cerebellum in children with ADHD. While some studies in animal and human models suggest that the certain brain structures are affected by chronic stimulant medication, it is unclear whether the cerebellum is also affected. The purpose of the current study was to determine if cerebellar morphology was different in treatment-naïve vs. chronically-treated children with ADHD.

Attention-deficit/hyperactivity disorder predominantly inattentive (ADHD-PI) and combined (ADHD-C) presentations are likely distinct disorders that differ neuroanatomically, neurochemically, and neuropsychologically. However, to date, little is known about specific white matter (WM) regions differentiating ADHD presentations. This study examined differences in WM microstructure using diffusion tensor imaging (DTI) data from 20 ADHD-PI, 18 ADHD-C, and 27 typically developed children. Voxel-wise analysis of DTI measurements in major fiber bundles was carried out using tract-based spatial statistics (TBSS). Clusters showing diffusivity abnormalities were used as regions of interest for regression analysis between fractional anisotropy (FA) and neuropsychological outcomes. Compared to neurotypicals, ADHD-PI children showed higher FA in the anterior thalamic radiations (ATR), bilateral inferior longitudinal fasciculus (ILF) and in the left corticospinal tract (CST). In contrast, the ADHD-C group exhibited higher FA in the bilateral cingulum bundle (CB). In the ADHD-PI group, differences in FA in the left ILF and ATR were accompanied by axial diffusivity (AD) abnormalities. In addition, the ADHD-PI group exhibited atypical mean diffusivity in the forceps minor (FMi) and left ATR and AD differences in right CB compared to healthy subjects. Direct comparison between ADHD presentations demonstrated radial diffusivity differences in FMi. WM clusters with FA irregularities in ADHD were associated with neurobehavioral performance across groups. In conclusion, differences in white matter microstructure in ADHD presentations strengthen the theory that ADHD-PI and ADHD-C are two distinct disorders. Regions with white matter irregularity seen in both ADHD presentations might serve as predictors of executive and behavioral functioning across groups.

Objective Studies of healthy individuals and those with cerebellar damage have implicated the cerebellum in a variety of cognitive and behavioral processes. Reduced cerebellar volume has been found in children with ADHD and differentially related to behavioral outcomes. In the current study, we sought to determine if reduced cerebellar vermis volume was present in children with ADHD-Combined type (ADHD-C) compared to controls and whether volume related to parent and teacher reported levels of ADHD symptomatology. Method 2T MRI images and parent and teacher reported ADHD symptoms were acquired for 32 children diagnosed with ADHD-C and 15 typically-developing controls. Participants were right-handed, had no comorbid diagnoses of learning disabilities, conduct disorder, or affective/mood disorder, and were between the ages of 9 and 15. Results Participants with ADHD-C showed significantly reduced volume in the posterior inferior vermis compared to controls. No statistically significant differences were observed for cerebral volume, anterior vermis volume, posterior superior volume, or total cerebellar volume. Regression analyses indicated that a significant amount of the variance in parent-reported BASC-II Hyperactivity and Attention and Conners’ Restless/Impulsive ratings was explained by volume of the posterior inferior vermis. Conclusions Consistent with previous studies, children with ADHD had reduced volume in the posterior inferior vermis. New findings emerged with reduced volume of the posterior inferior vermis predicting significant amount of the variance in parent-reported hyperactivity, attention, and restlessness/impulsivity. Thus, symptoms of hyperactivity and inattention in ADHD may be partially explained by reduced volume of the cerebellar vermis and its connections within the cerebrum.

The cause of attention-deficit/hyperactivity disorder (ADHD) has been linked to abnormalities in prefrontal-striatal-cerebellar networks, but the brain-behavioral correlates are relatively equivocal. Children with ADHD and healthy controls underwent MRI and neuropsychological testing. Brain cortical thickness was analyzed for the bilateral rostral and caudal anterior cingulate cortex (ACC). Inhibitory control was assessed with the Stroop Inhibition test, and ADHD symptom severity was assessed with parent and teacher behavioral questionnaires. Brain-behavior relationships were calculated between cortical thickness and behavioral measures with regression models. Children with ADHD had significant cortical thinning in the right rostral ACC but nonsignificant thinning in right caudal, left caudal, or left rostral ACC compared with healthy control children after statistical correction for multiple comparisons. Further, right rostral ACC thickness predicted a significant amount of the variance in parent- and teacher-reported symptoms of ADHD. Exploratory analysis showed that cortical thickness was not related to psychostimulant medication history. Symptoms of ADHD may be related to reductions in cortical thickness in the right anterior attention network, a region implicated in behavioral error detection, impulsivity, and inhibitory control.

These findings suggest that aberrant prefrontal and caudate volumes in ADHD-C may compromise functioning of the frontostriatal circuitry.