Increased muscle sympathetic nerve activity during delayed auditory feedback in humans

We examined the effect of mental stress on muscle sympathetic nerve activity (MSNA) by microneurographically measuring the MSNA of the tibial nerve while subjects read aloud. A delayed auditory feedback task (DAF) was employed with a delay interval of 200 ms and these performances were compared to those in the absence of DAF in five healthy men (28 +/- 2 years). The mean blood pressure was significantly elevated during reading both in the presence of DAF and in its absence, and the pressor response was more exaggerated in the presence of DAF than its absence. MSNA and plasma norepinephrine levels were significantly increased during reading in the presence of DAF but not in its absence, whereas heart rate was mildly increased at the same extent during reading in both the presence and absence of DAF. The results suggest that mental stress produces elevation in blood pressure and mediates the activation of sympathetic nerve activity.