Bimanual coordination in the ageing brain: Age-related differences in the motor system during bimanual coordination

Bimanual coordination is essential for many daily tasks and may decline with age due to structural brain changes, peripheral nervous system alterations, and muscle atrophy. My thesis explored age-related differences in structural and functional connectivity (SC and FC) and spectral power within the motor network, focusing on the premotor, primary motor, and parietal regions. I reviewed literature on FC and SC, finding that (1) changes in WM microstructural organization are associated with the rate of information transfer between brain regions, as assessed using event-related potentials (ERP); (2) slow-wave power changes in the delta, theta, and low-alpha frequency bands are often studied in relation to neuropathology and are associated with the structural abnormalities underlying specific disorders; (3) there is a close relationship between SC and FC at rest (without task performance) and during task execution. I examined age-related differences in resting-state cortico-cortical synchronization within the motor network in the beta frequency band and their relationship to age-related structural differences in these regions. I found that age-related differences in inter- and intra-hemispheric SC and WM microstructural organization in older adults were associated with age-related increases in FC between motor regions in the left hemisphere. Age-related FC increments were associated with poor bimanual coordination only in older adults. The results indicate that age-related changes in inter- and intra-hemispheric SC between motor areas affected left intra-hemispheric FC between pre- and primary motor cortex, and thereby the quality of bimanual coordination in older adults. I also studied alpha and beta spectral differences in brain activity in the motor and parieto-occipital regions between younger and older adults during unimanual and bimanual visuomotor tasks, and their associations with motor performance quality. I found a significant effect of age on spectral power in the alpha band over bilateral precuneus/cuneus, with older adults showing lower mean power and greater power modulations (the difference between dynamic and static force production) than younger adults during unimanual and bimanual performance. However, in the beta band, I observed a significant age difference in mean power only over the left PMC during bimanual performance. I identified significantly negative associations between power modulation and performance error in bilateral M1 and precuneusR for unimanual performance, as well as in bilateral M1, bilateral precuneus, and PMCL for bimanual performance. The results highlight the importance of the left hemisphere, particularly the PMCL, in determining bimanual performance quality in both groups. The results revealed that reduced ability to switch immediately from dynamic to static force production was associated with poorer motor performance in both groups. Since alpha power modulation in the bilateral precuneus was significantly associated with the quality of bimanual performance, reduced alpha power modulation in the precuneus in older adults compared to younger adults suggests that older adults experience greater difficulty with visual processing and recalling movement sequences, which may affect their motor performance. In conclusion, age-related changes in both unimanual and bimanual performance are linked to decreased alpha and beta spectral power in motor and occipital areas, heightened beta resting-state functional connectivity, and less coherent white matter microstructural organization of the structural connectivity between motor regions. The result suggests reduced inhibitory activity within left intra-hemispheric connections during bimanual performance in older adults, as well as diminished inhibitory control of the left premotor cortex over the right hemisphere, potentially leading to increased crosstalk between hemispheres, highlighting its pivotal role for bimanual coordination in the aging brain. Reduced spectral power and power modulation in the cuneus/precuneus cortex, and their association with poor motor performance in older adults, suggest a decline in visuospatial cognitive processing and in the orchestration between visual and motor networks.