Abstract
Paired associative stimulation (PAS) can induce plasticity in the motor cortex, as measured by changes in corticospinal excitability (CSE). This effect is attenuated in older and less active individuals. Although a single bout of exercise enhances PAS-induced plasticity in young, physically inactive adults, it is not yet known if physical activity interventions affect PAS-induced neuroplasticity in middle-aged inactive individuals. Sixteen inactive middle-aged office workers participated in a randomized cross-over design investigating how CSE and short-interval intracortical inhibition (SICI) were affected by PAS preceded by 3 h of sitting (SIT), 3 h of sitting interrupted every 30 min by 3 min of frequent short bouts of physical activity (FPA) and 2.5 h of sitting followed by 25 min of moderate-intensity exercise (EXE). Transcranial magnetic stimulation was applied over the primary motor cortex (M1) of the dominant abductor pollicis brevis to induce recruitment curves before and 5 min and 30 min post-PAS. Linear mixed models were used to compare changes in CSE using time and condition as fixed effects and subjects as random effects. There was a main effect of time on CSE and planned within-condition comparisons showed that CSE was significantly increased from baseline to 5 min and 30 min post-PAS, in the FPA condition, with no significant changes in the SIT or EXE conditions. SICI decreased from baseline to 5 min post-PAS, but this was not related to changes in CSE. Our findings suggest that in middle-aged inactive adults, FPAs may promote corticospinal neuroplasticity. Possible mechanisms are discussed.
Highlights
Neuroplasticity refers to the ability of the nervous system to undergo enduring morphological or functional change in response to the demands of its environment
SBprior % sedentary behaviour on the day prior to the session, MVPAprior % moderate-tovigorous physical activity performed on the day prior to the session of time on Area under RC (AURC) (p = 0.002), but the linear mixed model revealed no main effect of condition (p = 0.113) and no interaction between time and condition on AURC (p = 0.500)
We found no association between changes in corticospinal excitability (CSE) and short-interval intracortical inhibition (SICI)
Summary
Neuroplasticity refers to the ability of the nervous system to undergo enduring morphological or functional change in response to the demands of its environment. Regular physical activity initiates cellular and molecular processes related to neuroplasticity (Cotman and Berchtold 2002), leading to improvements in learning and memory (van Praag et al 1999). Non-invasive transcranial magnetic stimulation (TMS) is often used to probe corticospinal adaptations. Paired associative stimulation (PAS) can induce an effect similar to long-term potentiation, a mechanism of neuroplasticity that enhances synaptic communication, within the human corticospinal system (Stefan et al 2000). The effects of PAS on corticospinal excitability has been used as a measure of the propensity for neuroplasticity. More physically active subjects show a larger effect of PAS as compared to their less active counterparts (Cirillo et al 2009).
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