Research Review: Diffusion tensor imaging studies of attention‐deficit/hyperactivity disorder: meta‐analyses and reflections on head motion

<jats:sec><jats:title>Background</jats:title><jats:p>Diffusion tensor imaging studies have shown atypical fractional anisotropy (<jats:styled-content style="fixed-case">FA</jats:styled-content>) in individuals with attention‐deficit/hyperactivity disorder (<jats:styled-content style="fixed-case">ADHD</jats:styled-content>), albeit with conflicting results. We performed meta‐analyses of whole‐brain voxel‐based analyses (<jats:styled-content style="fixed-case">WBVBA</jats:styled-content>) and tract‐based spatial statistics (<jats:styled-content style="fixed-case">TBSS</jats:styled-content>) studies in <jats:styled-content style="fixed-case">ADHD</jats:styled-content>, along with a qualitative review of <jats:styled-content style="fixed-case">TBSS</jats:styled-content> studies addressing the issue of head motion, which may bias results.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>We conducted a systematic literature search (last search on April 1st, 2016) to identify studies comparing <jats:styled-content style="fixed-case">FA</jats:styled-content> values between individuals with <jats:styled-content style="fixed-case">ADHD</jats:styled-content> and typically developing (<jats:styled-content style="fixed-case">TD</jats:styled-content>) participants. Signed differential mapping was used to compute effect sizes and integrate WBVBA and TBSS studies, respectively. <jats:styled-content style="fixed-case">TBSS</jats:styled-content> datasets reporting no between‐group motion differences were identified.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>We identified 14 <jats:styled-content style="fixed-case">WBVBA</jats:styled-content> (<jats:styled-content style="fixed-case">ADHD</jats:styled-content><jats:italic>n</jats:italic> = 314, <jats:styled-content style="fixed-case">TD</jats:styled-content><jats:italic>n</jats:italic> = 278) and 13 <jats:styled-content style="fixed-case">TBSS</jats:styled-content> datasets (<jats:styled-content style="fixed-case">ADHD</jats:styled-content><jats:italic>n</jats:italic> = 557, <jats:styled-content style="fixed-case">TD</jats:styled-content><jats:italic>n</jats:italic> = 568). <jats:styled-content style="fixed-case">WBVBA</jats:styled-content> meta‐analysis showed both significantly lower and higher <jats:styled-content style="fixed-case">FA</jats:styled-content> values in individuals with <jats:styled-content style="fixed-case">ADHD</jats:styled-content>;<jats:styled-content style="fixed-case"> TBSS</jats:styled-content> meta‐analysis showed significantly lower <jats:styled-content style="fixed-case">FA</jats:styled-content> in <jats:styled-content style="fixed-case">ADHD</jats:styled-content> compared with <jats:styled-content style="fixed-case">TD</jats:styled-content> in four clusters: two in the corpus callosum (isthmus and posterior midbody), one in right inferior fronto‐occipital fasciculus, and one in left inferior longitudinal fasciculus. However, four of six datasets confirming no group‐differences in motion showed no significant between‐group <jats:styled-content style="fixed-case">FA</jats:styled-content> differences.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>A growing diffusion tensor imaging (<jats:styled-content style="fixed-case">DTI</jats:styled-content>) literature (total <jats:italic>N</jats:italic> = 1,717) and a plethora of apparent findings suggest atypical interhemispheric connection in <jats:styled-content style="fixed-case">ADHD</jats:styled-content>. However, <jats:styled-content style="fixed-case">FA</jats:styled-content> results in <jats:styled-content style="fixed-case">ADHD</jats:styled-content> should be considered with caution, since many studies did not examine potential group differences in head motion, and most of the studies reporting no difference in motion showed no significant results. Future studies should address head motion as a priority and assure that groups do not differ in head motion.</jats:p></jats:sec>