Motor cortex excitability responses to a simple visual reaction time task

It is known that Bereitschaftspotential or readiness potential, measured by electroencephalography, reflects the activity of the motor cortex prior to onset of a voluntary movement. However, measurement of this readiness potential using transcranial magnetic stimulation (TMS) and electromyography (EMG) has yet to be fully explored. This study used TMS to measure the excitability of the motor cortex projecting to the abductor pollicis brevis muscle in participants (n = 10) who were instructed to perform a rapid adduction movement of the thumb in response to a visuomotor signal on a computer screen. TMS was timed to stimulate at inter-stimulus interval times from 150 ms to 50 ms before movement onset and analysed by comparing mean motor evoked potential (MEP) amplitudes (reflecting corticospinal excitability) at times grouped between the ranges of 150–100 ms and 99–50 ms. Paired t-Tests revealed MEP amplitude was significantly higher (p < .05) forRTs 99–50 ms (2.76±1.73 mV)compared to 150–100 ms (1.86±1.15 mV). These results indicate changes in motor cortex excitability in preparation for a simple visuomotor reaction task, and further support of the readiness potential using TMS and EMG.