The influence of acute aerobic exercise on excitability and rapid plasticity in the primary motor cortex
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The aim of this thesis was to explore the influence of a single session of aerobic exercise on excitability changes and markers of short-term plasticity in the human primary motor cortex (M1). To that end, this thesis consists of 4 studies. In the first experiment, we explored whether acute exercise alone could modulate resting excitability in M1. We demonstrated that 20 minutes of moderate-intensity stationary biking could suppress intracortical inhibition and enhance intracortical facilitation in a non-exercised upper limb muscle for up to 30 minutes following exercise completion. Since decreases in inhibition are a necessary precursor to neuroplastic changes, we then investigated whether exercise could enhance the induction of rapid plasticity. We used paired-associative stimulation (PAS), a technique that reliably induces long-term potentiation (LTP)-like plasticity in M1 and found that a preceding bout of exercise enhanced the effectiveness of the intervention. Next, we examined whether these cortical changes were consistent across the entire cortical representation of the target muscle and if they were related to any measurable changes in motor performance. We paired exercise with a bimanual motor training task and observed that while performance was not enhanced compared to training alone, exercise facilitated training-related cortical excitability increases throughout the representation of the trained muscle. Finally, we demonstrated that exercise has opposite effects on the induction of long-term depression (LTD), suggesting that exercise is biased towards increasing excitability, and that this influence is evident even when exercise is performed following, rather than prior to, plasticity induction. This thesis demonstrates that aerobic exercise may optimize the conditions for experience-dependent plasticity to occur and provides a rationale for the use of exercise as an adjunct to interventions that aim to induce LTP in human motor cortex.