The current proposal seeks quantify neural inhibition using magnetic resonance spectroscopy (MRS) and transcranial magenetic stimulation (TMS) in older Veterans to identify how each measures contributes to aging-related changes in motor performance. Currently, over 56% (11.8 million) of Veterans are over age 60. Recent research has shown that aging is associated with decreased cortical inhibition and impaired hand motor function. However, this loss of inhibition is not an inescapable consequence of aging. Our previous work that healthy older adults who engage in regular physical activity show increased cortical inhibition and improved dexterity as compared to their sedentary age cohort. This indicates that aerobic training may reverse aging related changes in cortical inhibition and alteration of tonic levels of cortical excitability can have a powerful impact on motor performance in the aging brain. In the current proposal, we will enroll older adults to assess how different measurements (TMS and MRS) of the dominant inhibitory neurotransmitter in the brain – GABA differ in relation to motor control. During the MRS scan, participants will perform a motor learning task to assess change in GABA level throughout the acquisition session. These data will be compared with measures of cortical inhibition using TMS to quantify neurotransmitter receptor activity with respect to aging-related changes in motor performance. We will also be comparing the effects of an aerobic exercise intervention as compared to a contact matched stretching control. We believe this project is the first inquiry of its kind and will have an important impact in our understanding of aging-related neurophysiological changes in the brain and how we can remediate associated behavioral declines.