Effector-specific corticospinal modulation is preserved in older adults during proactive stopping: A novel Bayesian approach

Action cancellation is thought to decline with age, contributing to impairments in executive function and overall motor performance. While age-related deterioration of reactive inhibition (stopping an action in response to an external signal) is well-established, less is known about how ageing affects proactive inhibition (preparatory mechanisms which increase the chance that an action can be successfully stopped). This study examined how proactive and reactive inhibitory processes, assessed via changes in corticospinal excitability (CSE) and behaviour, vary as a function of ageing during a modified stop signal task. Participants made bimanual responses to an imperative signal and attempted to cancel one (selective stopping) or both (global stopping) responses, based on presentation of a stop signal. We compared reactive stopping to proactive stopping where cues informed participants which hand/s may have to stop. Using Bayesian model averaging analyses, we found that proactive cueing increased reaction times in both groups, indicative of proactive slowing. Furthermore, older adults exhibited greater slowing of ongoing action components (unilateral responses) following successful selective cancellation, compared to younger adults. However, there was strong evidence against age difference in CSE modulation. Specifically, both age groups exhibited effector-specific CSE modulation following proactive cues, with reduced MEP amplitudes in the hand that might need to stop, and increased amplitudes in the hand that was certain to respond (contralateral to the hand that may have to stop). These findings suggest that while ageing affects stopping behaviour, proactive inhibitory mechanisms which modulate CSE may remain preserved.