ebook_ADHD2019

The World Federation of ADHD Guide 31 DIFFUSION TENSOR IMAGING (DTI) A meta-analysis of whole-brain analyses DTI studies that combined voxel-based analysis (VBA) and tract-based spatial statistics (TBSS) documented widespread alterations in white matter integrity, especially in the right anterior corona radiata, right forceps minor, bilateral internal capsule, and left cerebellum 91 A later meta- -analysis on a larger set of TBSS studies found altered white matter microstructu- re, as reflected in low fractional anisotropy values, in the splenium of the corpus callosum (CC) that extended to the right cingulum, right sagittal stratum, and left tapetum. 92 These findings indicate that altered WM matter tracts that integrate the bilateral hemispheres and posteriorbrain circuitries play a crucial role in the pathophysiology of ADHD. FUNCTIONAL MRI (FMRI) Task-related fMRI studies using inhibitory control, working memory, and attentio- nal tasks have documented under-activation of frontostriatal, frontoparietal and ventral attention networks. 94 The frontoparietal network supports goal-directed executive processes while the ventral attention network facilitates attentional reo- rienting to salient and behaviorally relevant external stimuli. In reward processing paradigms, most studies report lower activation of the ventral striatum in ADHD compared to controls in anticipation of reward 67. ADHD is also associated with hyperactivation in somatomotor and visual systems, 94 which possibly compensates for impaired functioning of the prefrontal and anterior cingulate cortices. 95 Remission of ADHD has been associated with normalization of abnormalities as measured by activation during functional imaging tasks, 96 cortical thinning 97 and functional and structural brain connectivity. 98,99 RESTING-STATE MRI Resting-state MRI studies report that ADHD is associated with reduced or absent anti-correlations between the default mode network (DMN) and the cognitive control network, lower connectivity within the DMN itself, and lower connectivi- ty within the cognitive and motivational loops of the fronto-striatal circuits. 100 In simple words, individuals without ADHD tend to activate in a MRI scan during mindwondering this DMN. When requested to focus or execute an action, con- nections inside this DMN weaken while connections in the areas needed to the task are activated. This process seems to be disturbed in ADHD. Some previous investigations suggest that individuals with ADHD do not decrease activity in the