Simon B N Thompson, Souhir Daly, Alain Le Blanche, Malek Abidi, Charma Belkhira and Giovanni de Marco
Cortisol is an important hormone in the protective stress response system, the Hypothalamus-Pituitary-Adrenal (HPA-axis). It becomes especially salient in immune suppression syndromes such as multiple sclerosis and Cushing’s disease. Fatigue is a common symptom and mental and motor tasks are difficult and labored. The role of cortisol is mental and motor tasks and the recruitment of key brain regions in completion of these tasks is explored together with functional magnetic resonance imaging in healthy participants. Cortisol levels were found to be higher and had greater reduction in levels during mental versus motor tasks. Recruitment of brain-stem and hypothalamus regions, important in cortisol activity, was affected differently. At low cortisol levels, mental task participants had less activity in the regions than their physical task counterparts. When cortisol levels were higher, wider spread recruitment of these brain regions was seen in the mental task participants, and for the physical task participants, the spread was at comparative low levels of cortisol. It is concluded that cortisol is implicated in these brain regions supporting the Thompson Cortisol Hypothesis and that brain region recruitment is likely to be dependent upon factors including cortisol levels as well as perception of stress in the task. It is suggested that mental tasks are perceived more stressful than physical but demand higher cortisol levels to promote wider spread brain region activity. Implication for neurological disease includes the use of cortisol in the proposed development of a potential new diagnostic biomarker for early detection of neurological sequelae.