Effects of Acute Aerobic Exercise on Motor Cortex Plasticity in Individuals With a Concussion History

The impact of concussions was previously believed to be transient, however neurophysiological tools have revealed that long-term cognitive and motor declines persist past the acute phase of injury. Through a non-invasive brain stimulation method known as transcranial magnetic stimulation (TMS), long-term increases in gammaaminobutyric acid (GABA) mediated intracortical have been detected after sustaining a concussion. Such increases are known to suppress synaptic plasticity of the motor cortex. In healthy populations, acute aerobic exercise has the potential to enhance corticomotor excitability and intracortical networks that facilitate synaptic plasticity. This study used TMS to investigate the benefits of acute aerobic exercise on M1 plasticity in individuals with a history of concussions (>six months post-concussion). In a crossover design, participants performed a single bout of 20-minutes of moderate intensity biking, followed by a plasticity inducing method, known as paired associative stimulation (PAS), compared to PAS alone. TMS measures were collected at three time points: Pre-session, post-session one (five minutes post-PAS) and post-session two (30 minutes post-PAS). Excitability of the corticospinal networks was assessed by the motor evoked potential (MEP) and resting motor threshold (RMT). Intracortical networks that modulate cortical spinal output was measured through intracortical facilitation (ICF, 12ms), the cortical silent period (CSP), short-interval intracortical inhibition (SICI, 2ms) and long-interval intracortical inhibition (LICI, 100ms). Results demonstrated decreases in SICI in the exercise+PAS session (five minutes post-PAS), compared to the PAS alone session. MEP amplitudes increased in both the exercise+PAS session and PAS alone session. However, exercise did not further enhance the effects of PAS on MEP amplitude. No changes in CSP duration, LICI, ICF or RMT were found. Exercise-induced decreases in SICI reflect decreases in GABA-mediated inhibition, which plays a key role in synaptic plasticity. These beneficial impacts of exercise on brain plasticity may be used as an important consideration for normalizing the long-term subclinical motor declines that persist after sustaining a concussion