Changes in masseteric hemodynamics time-related to mental stress.

Mental stress may cause a dissociation of sympathetic outflow to different regions. However, it remains unclear how the sympathetic outflow to jaw muscles is related to other sympathetic outflow under mental stress. The objective of this study was to clarify the temporal relationship between the finger sweat expulsion elicited by mental stress and the hemodynamic and electromyographic changes in the masseter muscle. Healthy adult female volunteers participated in this study. Masseteric hemodynamic changes were closely time-related to mental stress, showing a decrease in oxygen saturation of muscle blood around the onset of mental stress. In contrast, EMG activity of jaw-closing muscles was not time-related to mental stress. These results suggest that mental stress induces hemodynamic changes that are not associated with EMG activity in the masseter muscle of healthy adult females.