Investigating the Impact of Sex Hormones in Multiple Sclerosis

The objective of this project is to systematically examine how hormonal fluctuations pre-menopause influence corticospinal excitability, motor learning, and motor fatigability in females with MS. The study is structured around the following specific aims: Aim 1: Quantify the effects of estradiol and progesterone levels on corticospinal excitability in pre- menopausal females with MS. We will elicit motor evoked potentials by cortical and subcortical stimulation of corticospinal axons using transcranial magnetic stimulation (TMS). Aim 2: Evaluate how hormonal fluctuations across menstrual phases impact motor learning ability in pre-menopause females with MS. Participants will be asked to perform a finger sequence motor learning task using visual feedback. The task will be performed using a computer keyboard. Participants will be asked to copy the numerical sequence on a monitor in front of them that pertains to a number on the keyboard with their fingers. Participants will be given three different sequences with equivalent difficulty at each session to avoid carry-over effects between visits. Aim 3: Determine the relationship between hormonal fluctuations and motor fatigability in pre-menopause females with MS. Participants will perform a maximal voluntary force (MVF). Participants will then be asked to pinch to 80% of their MVF, and maintain this hold for as long as possible1. The trial will end when the force drops below 40% MVF. Two trials in total will be performed. Average time to fatigue (40% MVF) and slope of the drop-off will be calculated as a measure of overall fatigue.