Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Kinesiology

Supervisor

Christie, Anita D.

Abstract

The purpose of this study was to perform a novel exploration of sex-based differences in corticospinal excitability and inhibition, with consideration of hormone phases. Thirty participants (15 females) attended two visits during different phases (low vs high). Responses evoked by single- and paired-pulse transcranial magnetic stimulation were recorded using electromyography from a hand muscle. Excitability was assessed via the motor-evoked potential and intracortical facilitation. Inhibition was assessed via the cortical silent period (CSP), short-interval (SICI), and long-interval intracortical inhibition (LICI). Each measure was compared between phases and sexes. Neither sex differed significantly across phases for excitability, nor inhibition for males. Females displayed significantly greater inhibition in the low phase (CSP: p=0.04). Overall, males and females had similar excitability. Males displayed significantly greater inhibition vs females for SICI (p=0.004) and LICI (p=0.008) but not CSP (p=0.28). Findings suggest both sexes could be equally included in research, during different hormone phases.

Summary for Lay Audience

Males and females differ anatomically and physiologically throughout the body, including the brain. These differences suggest potential differences in the communication from the brain to the muscle that is needed to produce a movement. Transcranial magnetic stimulation is a non-invasive tool commonly used in neurophysiology research to investigate the responsiveness and resistance of a muscle to the communication from the brain. Males have shown similar responsiveness, but greater resistance compared to females. This greater resistance often results in slower movement or worsened reaction times. However, these measures of communication from the brain to the muscle have not been extensively studied between sexes. Therefore, the purpose of the present study is to explore the sex-based differences in the responsiveness and resistance of a muscle to the communication from the brain, while considering the male (24-hr) and female (28-day) hormone cycles. A group of 30 young healthy adults (15 females) visited the laboratory two times during different phases of their hormone cycle. Transcranial magnetic stimulation was applied over the part of the brain that controls the hand. This stimulation initiated the communication from the brain and was recorded at the muscle in the hand. These values were compared between low and high hormone phases for each sex and were compared between males and females. No differences in responsiveness were seen between phases for either males or females. Females displayed greater resistance in the low hormone phase compared to the high hormone phase, while there were no differences in resistance between phases for males. When comparing sexes, males and females displayed similar responsiveness. Males displayed greater resistance compared to females. These results suggest that males and females could be equally included in neurophysiology research, during low or high phases of their hormone cycle. This was one of the first studies to compare these sex-based differences in communication from the brain to the muscle using various measures of responsiveness and resistance. Further research should continue to investigate these sex-based differences.

Download

Included in

Motor Control Commons

Share

COinS