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The structure and function of the brain are intrinsically linked, as changes in cognition correspond with known periods of structural remodeling across the lifetime of a person. This relationship is even more prevalent in neurodevelopmental conditions and neurodegenerative diseases, where changes in brain structure accompany disease symptoms and abnormal cognitive function. The cortex, a brain region responsible for higher-level executive functions like personality expression and decision making, is disproportionately impacted by common neurological conditions, with large amounts of degradation found in cortical areas. The study of cortical structure and its impact on function is dominated by measures of volume and thickness because the cortex is easily identifiable on standard structural images as the exterior gray matter of the brain. Findings from these studies have highlighted volume loss through healthy aging, cortical thinning during development, and accelerated changes in the cortical structure with dementia and Alzheimer’s disease. However, volumetric measures are unable to provide high levels of sensitivity to structural changes in the brain because they are an indirect measure of the microstructure itself.
A new technique for quantifying in vivo microstructural properties of brain tissue was recently developed called magnetic resonance elastography (MRE). MRE measures the mechanical properties of brain tissue to characterize tissue viscoelastic behavior through two properties of interest, shear stiffness and damping ratio. Taken together these properties can capture changes in tissue composition and organization, both of which have provided increased sensitivity and additional insight into the structure-function relationship in the brain. In previous studies, MRE measures have been linked to memory and cognitive performance, including studies where volume was not a significant predictor of cognition. Research applications of cortical MRE measures have been limited due to resolution and processing techniques that were unable to accurately resolve properties over the geometrically complex and thin structure.
This thesis aims to apply improved mechanical property recovery techniques to characterize the structure-function relationship in the cortex, addressing this research gap through three aims. The first aim is focused on determining aging effects on cortical mechanical properties during normal aging and their relationship to cortical controlled cognitive function. The goal of the second aim is to quantify longitudinal change in adolescent tissue mechanical properties, particularly the cortex, and determine how these changes relate to pubertal progression. Lastly, the third aim investigates the network relationship of mechanical properties in the cortex and association of network properties to cognitive performance. Together, this thesis highlights the utility of MRE to measure structural changes in the cortex and as a promising technique to sensitively study the cortical structure-function relationship.