ADHD is conceptualized as neurodevelopmental in origin although the mechanisms behind such altered development are not fully understood. Among structural MRI reports volumetric deficits in white matter are consistently replicated across studies. The working hypothesis for the present study is that the pathophysiology of Attention-Deficit/Hyperactivity Disorder (ADHD) may include abnormalities in white matter fiber bundle development.
METHOD AND MATERIALS
18 patients (M=8.9y) with a diagnosis of ADHD were compared to a control group which consisted of 15 subjects (M=9.1y). In addition to routine clinical scans 25 direction diffusion tensor images (DTI) with matching FSE and 3D SPGR sequences were obtained. DTI images were corrected for spatial distortion. FA images of all subjects were transferred into Talairach space. The intra subject registration was accomplished using a linear rigid-body transformation. A three channel segmentation was performed to obtain the white matter (WM) segmentation for each subject. Voxelwise statistical analysis was carried out using a two-tailed t test (p<0.01) followed by an extent threshold criteria of 100 contiguous voxels. FA analysis was corrected for WM content in each voxel.
Several brain areas were found to have lower FA values in ADHD patients as compared to normal controls. These included bilateral cerebellum, bilateral middle temporal gyrus, pons, bilateral pre-motor, right motor, left orbitofrontal, right fronto-cortico-striatal fibers, and corpus callosum.
We believe that this study is the first DTI study to report localized hemispheric WM bundle abnormalities in ADHD. Our results are in concordance with previously reported structural abnormalities for ADHD. The primary finding of frontal lobe WM abnormalities has been implicated in earlier neuroimaging studies of ADHD patients. Abnormalities in orbitofrontal cortex that constitute human brain limbic system may be involved in emotional processing. Motor, pre-motor and cerebellum findings may play a role in hyperactivity component. These findings suggest that ADHD is associated with significant decrease of FA in multiple brain areas known to control attention and motor activities.