Modulation of Corticospinal Motor Tract Excitability during a Fine Finger Movement under Psychological Pressure: A TMS Study

In the present study, the inuence of psychological pressure on corticospinal motor tract (CST) excitability was investigated using monophasic transcranial magnetic stimulation (TMS) during a ne nger movement. Nine participants performed a spatiotemporal tracing task using a small laser pointer attached to the right index nger. After seven acquisition trials, they performed two non-pressure trials followed by two pressure trials. A stress was successfully induced; state anxiety, heart rates, and galvanic skin response all increased under pressure. In terms of motor evoked potential (MEP) in the rst dorsal interosseous muscle, increases in amplitude and decreases in latency were shown under pressure. Moreover, whereas background electromyography (bEMG) before TMS failed to increase signicantly under pressure, the ratio of MEP amplitude to bEMG did increase under pressure. In addition, there was a signicant positive correlation between increased CST excitability and decreased performance accuracy from non-pressure to pressure trials. These results suggest that psychological pressure can facilitate the excitatory level of CST during performance of a ne motor skill and that CST excitation under pressure can relate to decreased performance.