P2-030: Hemispheric asymmetry of cortical thickness in individuals with no cognitive impairment and Alzheimer's disease

Abstract

Background: Human brain has hemispheric dominance for cortical functions such as cognition and motor, and some volumetric studies have suggested that there is structural brain asymmetry in healthy individuals. Recent voxel based morphometry (VBM) studies in AD have demonstrated that the left hemisphere is preferentially affected than the right. However, previous studies involved small sample size and their results were inconsistent. In contrast to VBM, cortical surface-based thickness measurement performed at the nodes of a 3-D polygonal mesh has the advantage of providing a direct quantitative index of cortical morphology and enabling more precise measurement in deep sulci. We tried to learn if there is asymmetry of cortical thickness in subjects with no cognitive impairment (NCI) and if AD preferentially affects right versus left hemisphere as the disease progresses and if there is any regional differences in this hemispheric asymmetry. Methods: Participants consisted of 148 NCI subjects and 196 AD patients. AD patients fulfilled the criteria for probable AD proposed by the National Institute of Neurological and Communicative Disorders and Stroke and the AD and Related Disorders Association. All the subjects underwent MRI including 3D volume images for cortical thickness analysis across the entire brain. Results: In NCI left hemisphere, relative to right hemisphere, showed cortical hypertrophy in language areas such Broca’s, Wernicke’s area, and basal temporal region, and motor cortex. In contrast, compared to left hemisphere, right hemisphere cortices were more hypertrophic in precuneus, cingulate gyrus, temoporparietal association cortex, parahippocampal gyrus and occipital lobe. In AD, this trend was generally maintained regardless of disease severity except that left hemisphere, relative to right hemisphere, showed cortical thinning in medial temporal region and anterior cingulate gyrus. Conclusions: Our results suggest that hemispheric dominance of cognitive and motor functions can be demonstrated by surface based cortical thickness measurements in normal cognitive group. The fact that hemispheric asymmetry of cortical thickness was generally maintained as AD progresses is consistent with the cognitive reserve theory. In addition, as the disease severity increases,medial temporal regions and anterior cingulate gyrus may degenerate in the left hemisphere more than the right.