callosum morphology and function in

The corpus callosum (CC) is the largest fiber tract in the brain and connects homological regions of the two cerebral hemispheres. Research with split-brain patients, whose CC has been surgically severed, and neurologically intact groups has shown that the CC is important for sustained and divided attention. Due to its role in attention, the CC is of interest to clinical conditions in which attention is affected, such as attention deficit hyperactivity disorder (ADHD). Although the size of the CC has been examined in children and adolescents with ADHD, the results have been inconsistent. Therefore, the first of three studies in this thesis synthesized the current research in a metaanalysis, which analyzed the data from 13 studies that examined CC area in children and adolescents with ADHD, when compared to healthy controls. This study found that the splenium, the most posterior region of the CC, was smaller in ADHD and the rostral body, an anterior region, was smaller in boys with ADHD compared with controls. Thus, there is evidence for differences in area in both the anterior and posterior regions of the CC in ADHD. It was not known whether these differences persist into adulthood, however, because CC size had not been examined in adults with ADHD. Therefore, the second study examined CC area and structural integrity in young adults with ADHD compared with healthy controls using magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI), respectively. The difference in the size of the splenium was not present in this adult sample, 1 American spelling is used throughout the thesis in order to be consistent with the published papers which have been published or prepared using American spelling.