Running head: AGE-RELATED CHANGES UNDERLYING FINE MOTOR CONTROL 1 Investigating Age-Related Changes in Motor Cortex Excitability Underlying Fine Motor Control

There is an age-related decline in fine motor control. Functional changes in the primary motor cortex may help explain the age-related decline in fine motor control. Both facilitatory and inhibitory processes in the motor cortex are important for the execution of movement. The aims of the current study were to systematically and comprehensively investigate age-related changes in motor cortical facilitation and inhibition and to investigate the role of these processes in fine motor control. In healthy younger (n = 26) and older adults (n = 21), fine motor control was measured using the Purdue pegboard and a unimanual circle task. Paired-pulse transcranial magnetic stimulation (TMS) was used to measure short-interval intracortical facilitation (SICF) and short-interval intracortical inhibition (SICI) acting on an intrinsic hand muscle (important for fine motor control). Results show no difference in SICF between younger and older adults. When SICI was measured using TMS parameters corresponding to high levels of SICF, older adults showed less SICI than younger adults. When SICI was measured using TMS parameters corresponding to low levels of SICF, there was no difference in SICI between younger and older adults. Older adults showed a relationship between SICI and fine motor control, suggesting greater SICI results in better performance on fine motor control tests. Together findings suggest a complex interaction between the balance of facilitation and inhibition, and that this is affected by age and influences fine motor control.