Psychological pressure facilitates corticospinal excitability: Motor preparation processes and EMG activity in a choice reaction task

Abstract

The effects of psychological pressure on corticospinal excitability and muscular activity were investigated in a two-choice reaction task that involved voluntary right index finger movements. In order to induce pressure, participants were given instructions that combined a performance-contingent cash reward, a penalty, and performance comparisons. Following practice, 11 participants performed 40 non-pressure and 40 pressure trials. Results showed successful stress induction, as indexed by significant increases in state anxiety, pulse rate, and galvanic skin response under pressure. Significant increases in the amplitude of the motor evoked potential of the right abductor pollicis brevis (APB) occurred under pressure. The maximum EMG amplitudes of APB and the first dorsal interosseous (FDI) muscle also increased significantly under pressure. These results suggest that descending excitatory volleys in the corticospinal motor tract during the motor preparation processes and peripheral motor unit activities in the reaction task are both separately excited by stress responses under pressure. Reaction times measured by EMG onset of the FDI were unchanged in accordance with corticospinal and EMG excitations under pressure, indicating generation of inefficient motor control energy for movement output.

Keywords:

• electromyography
• motor evoked potential
• reaction time
• stress
• transcranial magnetic stimulation