Background: Thompson Cortisol Hypothesis proposed yawning correlates with rises in cortisol levels. Cortisol is fundamental to immune system regulation. Pathological yawning is a symptom of MS. Electro-myographical activity (EMG) in the jaw muscles rises when stretched; and is likely to be correlated with yawning, and potentially correlated with cortisol levels in healthy people and in MS.
Objectives: Investigate possible link between EMG in jaw muscles with rises in saliva cortisol levels during yawning.
Method: Randomized controlled trial: 11 male and 15 female volunteers aged 18-53 years exposed to conditions that provoked a yawning response. Saliva samples were collected at start and after yawning or at the end of stimuli presentations if the participant failed to yawn, and EMG data was collected during rest and yawning phases and is novel. Yawning susceptibility scale, Hospital Anxiety and Depression Scale, General Health Questionnaire, demographic, health details were collected for yawners and non-yawners, between rest and yawning phases. Exclusion criteria: chronic fatigue, diabetes, fibromyalgia, heart condition, high blood pressure, hormone replacement therapy, multiple sclerosis, stroke.
Results: Significant differences between saliva cortisol samples. Yawners, t(11) = -3.115, p = 0.010; F (1, 11) = 13.680 p < 0.025, and non-yawners, t(14) = -2.658, p = 0.019; F (1, 14) = 4.758 p = 0.047. Moderate, though not significant, correlation between cortisol change (from sample 1 to 2) and EMG score: r (7) = 0.440, p = 0.071. Significant difference in EMG readings between yawners and non-yawners, t (7) = -2.959, p = 0.021.
Conclusions: Thompson Cortisol Hypothesis is supported, and EMG is correlated with yawning and elevated cortisol levels. Longitudinal study is planned with MS patients to develop an early diagnostic tool.

Keywords: Cortisol, Electro-myography, EMG, Neurological disorder, Yawning.