Beyond pictures: Brain imaging and neurobiological correlates in developmental disorders

Autism Spectrum Disorder (ASD) and Attention-Deficit/Hyperactivity Disorder (ADHD) are the two most frequently diagnosed developmental conditions. Given their high prevalence, frequent chronic morbidity, and related functional disability, ASD and ADHD are important public health concerns. This is the background to the considerable effort expended to search for neurobiological correlates that might be useful as biological targets for new treatments and intervention strategies. Similar to most psychiatric conditions, ASD and ADHD are characterized by substantial clinical and etiological heterogeneity, which may hamper the identification of potential neurobiological markers. Studies on brain changes using magnetic resonance imaging (MRI) techniques have enormously enhanced our knowledge of typical brain development and related changes in neurodevelopmental disorders. In this thesis, we used structural and functional MRI to study neurobiological correlates of both ASD and ADHD, both qualitatively and quantitatively. Our findings support the hypothesis that clinical heterogeneity in ASD and ADHD is accompanied by similar variation in the associated neurobiological substrates: these range from anomalies large enough to be qualitatively noticeable in anatomical MRI scans, to more subtle changes at the group level that are invisible to the human eye, but can be characterized using quantitative assessments of brain morphometry. Our findings suggest specific neurobiological mechanisms may be involved in the pathogenesis of ASD and ADHD