Age-related changes in interlimb coordination

Age-related changes in motor performance have often been associated with functional decline with advancing age such as general motor slowing, degraded attentional capacity, and declined physiological inhibitory control. The overarching aim of the current series of empirical studies was to investigate the contribution of these functional alterations to agerelated changes in motor function. The first part of the study investigated age-related changes in inter-limb coordination and the associated attentional cost using a dual-task paradigm. The primary task involved the coordination of arm and leg movements performed by limbs on the same (ipsilateral) or opposite (contralateral) sides of the body. Difficulty of the primary task was manipulated by varying movement direction (isodirectional vs non-isodirectional) and movement frequency, with attentional cost being reflected in responses to a secondary probe reaction time task. The results showed that the performance of older adults selectively deteriorated depending on task difficulty. That is, the age-difference was pronounced in the most attentionally demanding' condition in which the movement frequency was highest and the motor task was performed simultaneously with a reaction time task. The second part of the study used electroencephalography (EEG) to provide a direct measure of the eNS activity associated with mental resource allocation in older adults during the performance of the interlimb coordination task. Attentional resource allocation was assessed by Event-Related Potentials (ERPs) during concurrent performance of interlimb coordination tasks and a visual oddball task. The amplitude of the P3b component of the ERP has been associated with the allocation of attentional resources. For both young and older adults coordination performance was less stable and visual reaction times (RTs) were longer during the coordination of ipsilateral limbs than contralateral limbs. Although older adults showed slower RTs to targets in the visual odd ball task, they exhibited similar patterns in P3b latency and amplitude to younger adults. Of particular interest was higher a P3b amplitude at the frontal sites in older adults, suggesting an increased cognitive monitoring of performance with aging. In the last part of the research the modulation of cortical activity during interlimb coordination was examined using transcranial magnetic stimulation (TMS). The length of the silent period (SP) following a motor evoked potential (MEP) was used as a measure of corticospinal inhibition during the interlimb coordination task. As expected, older adults showed less stable coordination performance than younger adults during production of non-isodirectional patterns. SP duration was lengthened, indicating increased inhibition, in the young group during the performance of the ipsilateral non-isodirectional pattern. In contrast, the older group showed a consistent level of cortical inhibition across conditions. These results suggest that deterioration in motor performance with advancing age might be associated with the declined ability to modulate inhibitory function.