P101. Impact of aging on motor control networks underlying movement selection and initiation

Abstract

Introduction Healthy elderly adults typically show greater regional activity in frontoparietal brain regions relative to young adults when performing motor control tasks ( Ward and Frackowiak, 2003 , Vallesi et al., 2011 ). However, the functional role of enhanced activity within the motor network is still a matter of debate. One hypothesis is that higher levels of neural activity reflect a compensatory mechanism to account for age-related decline in neural networks. We, therefore, used a systems-level approach to investigate networks dynamics underlying motor control in young and elderly subjects. We hypothesized that advanced aging is associated with reduced connectivity in the basic motor network, which is compensated by stronger influence of non-primary motor areas like prefrontal cortex. Methods We scanned 12 young (age 22–33) and 12 elderly subjects (age 52–74) employing a computerized task involving both basic (finger tapping) and higher motor control processing (internally and externally cued movement selection and initiation). Dynamic Causal Modelling (DCM) for fMRI was used to assess effective connectivity in a bilateral frontoparietal network comprising dorsolateral prefrontal cortex, dorsal premotor cortex, intraparietal cortex and primary motor cortex. Results Elderly subjects showed a significant slowing in movement selection and initiation. This slowing was accompanied by increases in both regional brain activity and effective connectivity between frontoparietal brain regions in elderly compared to young subjects. However, within the group of elderly subjects, coupling strengths of premotor cortex with primary motor cortex and intraparietal cortex decreased with advancing age, whereas connectivity between prefrontal and premotor cortex increased as a function of age. Discussion Network interactions underlying visuomotor transformation (parietal-premotor) and motor execution (premotor-primary motor cortex) follow an U-curve relationship: Connectivity is generally elevated in old relative to young subjects, yet decreases with advanced aging. In contrast, prefrontal influences on premotor cortex increase with advanced aging. These findings are in line with the ”posterior to anterior shift theory” described for regional brain activity, thereby extending it to network interactions related to higher motor control ( Davis et al., 2008 ).