Salivary Cortisol as a New Biomarker for a Mild Mental Workload

Recent psycho-physiological studies have revealed close relationships between human mental stresses and secretion of hormonal and immunological substances. However, a precise elaboration of fluctuations in the secretion of these biomarkers in the time series against stress; especially against a rather mild stressful task is not yet clearly illuminated. In this study, we used the cortisol, a major glucocorticoid, as a biomarker of mental stress for (1) illustrating the precise stress-response in the time series, and (2) investigating a congruity of cortisol as the biomarker for a mild mental workload. Ten male university students were inscribed to conduct a simple, easy, and monotonous mental arithmetic task for about an hour with intermissions, so as to emulate a mild mental workload. As a result, salivary cortisol depicted an accumulative increase during mild mental workloads, while no marked difference was obtained in the heart rate and its variability. It suggests the slow and long-lasting properties in the stress-response of the cortisol unlike as in autonomous nervous system indices, and therefore plausibly demonstrates the possible candidacy of cortisol as a biomarker for a mild mental load.