Functional Neuroimaging Studies of Simple Finger Movements in Healthy Development and Aging and in Children with Dyslexia

Abstract

The functional neuroanatomy of the motor system underlying finger movements has been thoroughly elucidated in young adults. However, less is known about this system at younger and older ages, and in disorders. This dissertation presents three studies that were designed to address the functional anatomy of simple finger movement in three groups, older normal adults, children and children with the reading disability developmental dyslexia. To investigate age-related effects, we first conducted a meta-analysis on within-group data from older and young adults performing regularly paced finger-movement tasks. In our second study, we investigated the motor system in children and young adults with functional magnetic resonance imaging (fMRI) during irregularly paced finger movements of the thumb. We found that all groups recruited contralateral primary sensorimotor cortex (SM1), supplementary motor area (SMA), and ipsilateral cerebellum. Compared with young adults, we found that older adults and children exhibited greater recruitment of SM1 ipsilateral to the side of movement and caudal SMA, and weaker recruitment of rostral SMA. We also found weaker activation in children compared with young adults in basal ganglia. Overall, these findings suggest that some of the changes to the motor system that occur between childhood and young adulthood are mirrored in older age, while others are unique to each side of the lifespan. To investigate dyslexia-related effects, we acquired fMRI data in children with and without this reading disability as they performed the same irregularly paced finger-movement task. We then examined task-evoked activation and functional connectivity (FC) using motor areas as seeds. Both groups exhibited task-evoked activation in contralateral SM1, SMA, and ipsilateral cerebellum, and we did not find between-group differences. However, we found several functional connections that were different between groups, most notably a functional disconnection in children with dyslexia between the right cerebellum seed and left SM1, suggesting compromise of the cortico-cerebellar loop. Overall, these findings illustrate that the functional neuroanatomy of the motor system is age-dependent and, to a more limited extent, dyslexia-dependent.