We examined the influence of right handed pinch grips and the effect of a motor training on motor cortex excitability of the left first dorsal interosseus muscle (FDI). TMS single and paired pulses were applied over the right human motor cortex (M1) during and after right handed pinch grips with low force. In another experiment, these stimulations were performed before and after a 30-minute right handed pinch grip training.
Results: MEP amplitudes in left FDI were reduced when TMS single pulses were applied during the pinch grip. Simultaneously, motor cortex excitability was enhanced but returned to baseline after the training period.
Conclusion: Phasic pinch grips of the right hand exert an inhibiting effect on the corticospinal excitability of the ipsilateral motor cortex and lead to an increase of intracortical excitability. These changes are distinct and independent of each other. Motor training has an interhemispheric effect on intracortical excitability.