From Local Inhibition to Distributed Motor Control in Aging

Background: Aging-related changes in motor performance are associated with a widespread reorganization of the motor network. Despite extensive research on altered brain activity patterns in aging, the underlying neurophysiological mechanisms driving these reorganizational changes remain incompletely understood, particularly regarding the role of inhibitory control. Methods: We here combined transcranial magnetic stimulation (TMS) and electroencephalography (EEG) to examine aging-related alterations in local excitability, oscillatory dynamics, and neural coupling in the motor system. Brain responsivity was probed by applying single-pulse TMS to the primary motor cortex (M1) in younger and older subjects at rest. Results: Our findings indicated reduced cortical excitability in the stimulated M1 of older participants, consistent with an age-related reduction of GABAergic inhibitory control. Phase-locking analyses revealed reduced intra- and interhemispheric coupling in lower frequency bands, suggesting decreased inhibitory output from the stimulated M1. Moreover, older individuals demonstrated less localized event-related desynchronization (ERD) with greater power decreases in the prefrontal cortex contralateral to the stimulation site, indicating enhanced prefrontal involvement in the aging motor system. Conclusions: Together, these findings underline the relevance of alterations in inhibitory processes in the motor network in aging and point to a shift from an automatic, locally driven towards a broader, putatively more cognitively controlled sensorimotor processing in older adults.