An investigation of verbal and spatial working memory in young people with ADHD-Combined Type and Dysthymic Disorder using fMRI
Document TypePhD thesis
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© 2015 Dr. Vilgis Veronika
Introduction: Paediatric Attention-deficit/hyperactivity Disorder (ADHD) and Dysthymic Disorder (DD) are disorders that present very differently clinically but have both been associated with deficits in attention, executive function and emotion regulation. Furthermore, neuroimaging investigations have implicated atypical brain structure and function in fronto-striatal, fronto-limbic, fronto-parietal and fronto- cerebellar networks in both ADHD and depressive disorders. It is currently unclear whether abnormalities in these networks are primarily shared across disorders or show disorder-specific pathophysiology. This thesis addresses this gap in the literature by directly comparing a group of young people with ADHD with a group of young people with DD as well as a group of typically developing young people. Methods: A total of 43 male children participated in the study, comprising twelve boys with a diagnosis of ADHD, twelve boys with a diagnosis of DD and 19 typically developing (TD) male controls. Both clinical groups were matched for symptoms of inattention to ensure symptom overlap. All participants underwent functional magnetic resonance imaging while performing a working memory task with a verbal and spatial processing component. Load was manipulated across tasks with each task consisting of two levels, a low and high load condition. Results: During the spatial task the ADHD group exhibited less activation in fronto-parietal regions compared to both the TD and the DD group. All three groups showed load-dependent activation patterns in posterior regions but the direction of activation was different across groups. In the verbal task the DD group exhibited less activation in left prefrontal cortex (PFC) and right temporoparietal regions during the low load condition and increased activation in right parietal regions compared to TD and ADHD participants during the high load condition. Follow-up analysis revealed that during the verbal high load condition a significant difference between contributions of left and right PFC was found between the DD and TD group. Greater problems in regulating emotion were associated with fronto-parietal regions during SWM. Discussion: The results presented in this thesis suggest primarily disorder-specific pathophysiology during working memory. Differences between the TD and the ADHD group were more apparent during the spatial task and between DD and TD during the verbal task. From a network perspective both disorders may be characterised by atypical function of the same network but region-specific differences within the network may exist.
KeywordsADHD; magnetic resonance imaging; depression; working memory; children and adolescents
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