Sex-based Differences In Corticospinal Excitability And Inhibition

Males and females differ in anatomy and physiology at many levels of the body, including the brain, which could influence the communication from the brain to the muscle, impacting movement control. However, sex-based differences in excitability and inhibition within the corticomotor pathway have not been extensively studied. PURPOSE: To examine sex-based differences in corticospinal excitability and inhibition. METHODS: Thirteen individuals (23.9 ± 2.1 yrs) 8 males, 5 females, participated in the present study. Males were tested around the same time of day in the afternoon and females were tested during the same phase of their menstrual cycle (mid-follicular; day 7.6 ± 0.5). Electromyography was recorded from the first dorsal interosseous muscle in response to TMS of the contralateral motor cortex. Single-pulse stimuli were used to assess excitability via the motor-evoked potential (MEP) and inhibition via the cortical silent period (CSP). Additionally, paired-pulse stimuli were used to assess excitability via intracortical facilitation (ICF) and inhibition via short-interval intracortical inhibition (SICI) and long-interval intracortical inhibition (LICI). All outcome measures were compared between males and females. RESULTS: Males had similar levels of excitability compared with females via MEP (2.9 ± 1.0 mV vs 3.06 ± 1.37 mV; p = 0.86; d = 0.11) and ICF (68.0 ± 70.7% vs 36.7 ± 100.1%; p = 0.52; d = 0.38). Inhibition was also similar between males and females, as assessed by CSP duration (124.3 ± 30.6 ms vs 91.6 ± 43.9 ms; p = 0.16; d = 0.90), SICI (-62.9 ± 26.0% vs -59.3 ± 30.5%; p = 0.82; d = 0.13), and LICI (-81.4 ± 18.2% vs -71.6 ± 26.4%; p = 0.47; d = 0.46). CONCLUSION: No significant differences in corticospinal excitability or inhibition were observed between males and females, when controlling for lower hormone fluctuation timepoints. However, considering effect sizes, CSP may reach significance with a greater sample size. Natural Sciences and Engineering Research Council of Canada (NSERC) RGPIN-2019-05127