100 Philosophie und Psychologie 150 Psychologie 153 Kognitive Prozesse, Intelligenz
Attention deficit hyperactivity disorder is a chronic childhood onset neuropsychiatric disorder characterized by developmentally inappropriate inattentiveness, impulsivity and hyperactivity, impairing multiple areas of life. Distinct deficits in cool and hot EF were proposed to represent a source of impairment in ADHD and shown to relate to the core symptoms of ADHD. In particular, deficits in cool EF, including set shifting and working memory, were proposed to compromise self-regulation, managing multiple tasks of daily life, and academic and occupational outcome. Deficits in hot EF, including reward anticipation processing, represent a second pathway of impairment in ADHD and were shown to compromise motivation and may thus impede learning abilities and work performance. Diminished reward anticipation processing was shown to contribute to impulsive behavior that can trigger adverse and dangerous life events typically experienced by individuals with ADHD. The central role of cool and hot EF in ADHD was the starting point of the studies presented in this thesis with the aim to address limitations of previous findings in children and adults with ADHD.
Three cross-sectional studies investigating individuals with ADHD-CT were conducted. To address limitations of the previous literature, distinct age groups were chosen to investigate cool EF (Study I) and hot EF (Study II and III) in drug-free individuals with ADHD-CT.
Study I investigated cool EF, in particular set shifting and working memory in adults with ADHD-CT. Compared to healthy controls, adults with ADHD showed significant alterations in both attributes. Subgroup comparisons between patients with pure ADHD and patients with ADHD plus comorbidity revealed no significant differences. These results suggest that alterations in set shifting and working memory are rather related to ADHD than to comorbidity.
Study II evaluated a child-friendly incentive delay (CID) task in comparison to the MID task by Knutson, Adams et al. (2001). In line with my hypothesis, both tasks elicited significant ventral striatal activity in healthy adults during reward anticipation. Accordingly, no differential behavioral task effects appeared (i.e. reaction times, accuracy rates or the total amount of gain). Moreover, the CID task elicited significant ventral striatal activity in healthy children. Taken together, these findings demonstrate evidence for the validity of the CID task. Thus, the CID task can be recommended for the application in future studies in reward anticipation processing in children and adults.
Study III investigated reward anticipation processing in children and adults with ADHD using the MID and the CID task. Reward anticipation elicited decreased ventral striatal responsiveness in adults but not in children with ADHD-CT. Moreover, children and adults with ADHD showed reduced ventral striatal grey matter volumes. Taking these grey matter differences into account, the results remained stable. These results suggest that decreased ventral striatal responsiveness during reward anticipation is present in adults but not in children with ADHD-CT, irrespective of structural characteristics. Longitudinal studies should therefore examine whether ventral striatal hypoactivity is an ADHD correlate that develops during the course of illness.
Taken together, the presented findings support the view of ADHD as a heterogeneous disorder related to cool and hot EF deficits. In particular, the results suggest cool EF impairments in set shifting and working memory in adults with ADHD-CT, irrespective of comorbidity. Findings in hot EF, in particular reward anticipation processing, suggest diminished reward sensitivity in adults with ADHD-CT, whereas no significant differences emerged between children with ADHD-CT and healthy controls. To the best of my knowledge, this is the first study on reward anticipation in drug-naïve children with ADHD-CT that also considers potential effects of brain structure. The cross-sectional results of this thesis facilitate hypothesis driven longitudinal studies that combine investigations of cool and hot EF in individuals with ADHD-CT.
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