Modified impulse diminishes discomfort of transcranial electrical stimulation of the motor cortex

Transcranial electrical stimulation of the motor cortex has been developed in 1980 for electrophysiological assessment of the descending pathways. However, the widespread use of this procedure is limited by its painfulness due to simultaneous excitation of the sensory receptors and muscles of the scalp, especially if higher stimulus strengths are necessary in patients with motor deficits to evoke electromyographic responses. The present invention concerns a device which allows modification of the impulse delivered by a commercially available motor stimulator. By interruption on the exponentially decreasing impulse, "cutting" it after a freely selectable time by a low resistant short circuit on the patient's side, discomfort due to excitation of the sensory receptors and muscles of the scalp can be diminished with identical electromyographic responses regarded amplitudes and latencies of the potentials, thus making electrical stimulation less painful. Considering the applied charges we found a marked reduction of charge per phase using the modified impulse as compared to the original one with the difference increasing linearily depended on the preselected voltage.