| Early investigations into the organization of brain function had been hampered by a number of limitations, including an inability to study healthy subjects, to perform a non-invasive study, to examine individual subjects, or to achieve high spatial/temporal resolution. Recent advances in neuroimaging, however, have made tremendous contributions to the study of human brain function. Functional magnetic resonance imaging, in particular, provides a non-invasive tool by which the high resolution visualization of activity in the individual brain, be it healthy or diseased, can be achieved.; In this dissertation, blood oxygen level dependent functional magnetic resonance imaging was used to study the cortical organization of lexical-semantic language networks in three groups of subjects: healthy controls, left hemisphere stroke patients recovering from aphasia, and patients with left perisylvian arteriovenous malformation and no history of developmental disorder.; As a group, control subjects exhibited left hemisphere dominance during language task performance. Individually, lateralization varied continuously from left hemisphere dominance to bilateral representation. Gender differences were observed in the lateralization of activity during the performance of verb generation and picture naming tasks. During these tasks, language lateralized to the left hemispheres of male subjects, while approximately half of the female subjects had left hemisphere representation and half had bilateral representation.; In recovering aphasic stroke patients, functional language activity significantly increased in the right hemisphere and non-significantly decreased in the left hemisphere, compared to the normal group. Bilateral language networks resulted from partial restitution of damaged functions in the left hemisphere and activation of compensatory areas in the right hemisphere. Failure to restore any language function in the left hemisphere led to predominantly right hemispheric networks in some individuals. However, better language recovery, was correlated with bilateral networks, rather than right hemisphere predominant networks.; In patients with left hemisphere AVM and no history of developmental disorder, language function lateralized to the right hemisphere when compared to control subjects. The degree of right hemisphere recruitment non-significantly exceeded that observed in adult stroke patients. Presumably, patients with left perisylvian AVM recruited the right hemisphere into language processing networks during early development, perhaps in response to congenitally aberrant circulation. |
