Motor evoked potentials (MEPs) were recorded from first dorsal interosseous muscle of non-dominant hand in response to contralateral transcranial magnetic stimulation (TMS) in seven right-handed healthy volunteers during relaxed muscles (without electromyorgaphic activity and zero force production), isometric index finger abduction (20% of individual measured maximum voluntary contraction in direction of abduction) and co-activation of antagonist muscles (simultaneously activated antagonist muscles, matching level equal to 20% of individual measured maximum voluntary contraction in direction of abduction by increasing the angle stiffness without producing of external force). The excitability of motor cortex was assessed by the amplitudes of MEPs recorded in response to increasing stimulation intensity: 100%, 110%, 120%, 130%, 140% of individually measured motor threshold at relax. The aim of the present study was using the method of transcranial magnetic stimulation to investigate the effect of different types of muscle activity in non-dominant hand. The secondary purpose was to compare new collected data with our previous data about dominant hand. At non-dominant hand we found significant changes between relax condition and each of the two active motor tasks almost at all five investigated TMS intensities. Also, we found that MEP amplitudes during abduction were significantly bigger than MEP amplitudes during co-activation of antagonist muscles, both in non-dominant hand and in dominant hand. We observed changes between MEP amplitudes of non-dominant and dominant hand during the performance of the same motor task.
Motor facilitation during action observation: a magnetic stimulation study