Hormone Phase Considerations On Corticospinal Pathway Measures In Males And Females

Previous evidence suggests that hormones may impact excitatory and inhibitory neurophysiological outcomes differently in males and females. However, sex- and hormone-related differences in excitability and inhibition of the corticomotor pathway have not been widely studied. PURPOSE: To examine sex-related differences and hormone phase influences on corticospinal excitability and inhibition. METHODS: Thirty participants, 15 males (23.3 ± 1.3 yrs), 15 females (22.9 ± 2.8 yrs), visited the laboratory for 2 visits, one in each of their high and low hormones phases. Males were tested in the morning and in the afternoon, while females were tested in the mid-follicular and in the mid-luteal phase of their menstrual cycle. Electromyography was recorded from the first dorsal interosseous muscle in response to transcranial magnetic stimulation. Single-pulse and paired-pulse stimuli were used to assess excitability via the motor-evoked potential (MEP) and intracortical facilitation (ICF) and inhibition via the cortical silent period (CSP), short-interval intracortical inhibition (SICI), and long-interval intracortical inhibition (LICI). All outcome measures were compared between phases within each sex and between males and females with averaged phase data. RESULTS: No significant differences in excitability were found between sexes (MEP: p = 0.09, d = 0.65; ICF: p = 0.65, d = 0.17), nor between phases for males (MEP: p = 0.67, d = 0.12; ICF: p = 0.24, d = 0.32) or females (MEP: p = 0.25, d = 0.31; ICF: p = 0.95, d = 0.02). Males displayed greater inhibition compared to females in SICI (p = 0.004, d = -1.15) and LICI (p = 0.008, d = -1.12) but not CSP (p = 0.28, d = 0.40). Within males, inhibition did not differ across phases (CSP: p = 0.13, d = 0.41; SICI: p = 0.33, d = 0.26; LICI: p = 0.70, d = 0.11). In females CSP (p = 0.04, d = 0.60) indicated greater inhibition in the low hormone phase, however there was no significant difference between phases for the other measures of inhibition (SICI: p = 0.80, d = 0.07; LICI: p = 0.63, d = 0.13). CONCLUSION: These results suggest hormone phase may be an important consideration for CSP, but not for other measures of corticospinal inhibition or for measures of excitability. Supported by: Natural Sciences and Engineering Research Council of Canada (NSERC) RGPIN-2019-05127