[Rules of application and mode of action of transcranial direct current stimulation in neurorehabilitation: primary motor cortex]

Abstract

Transcranial direct current stimulation (tDCS) is an emerging technique of non-invasive brain stimulation that has been found useful in facilitating treatment of various neurological disorders, especially stroke. Currently available criteria for single application of several minutes-long stimulation at 1-2 mA have been considered safe. However, knowledge regarding safety parameters of repeated and long-term electrical stimulation is so far limited. Studies on the use of tDCS focus predominantly on the motor cortex. They demonstrate that weak direct current is capable of eliciting cortical excitability changes which occur during and after stimulation. The nature of these changes is specific for current polarity - anodal stimulation enhances excitability, and cathodal reduces it. Studies indicate that tDCS effects are generated by polarity-driven alterations of membrane potentials and efficacy modulations of specific neuronal receptors. According to interhemispheric competition models, possible mechanisms underlying functional improvements due to stimulation in patients with stroke are attributed to tDCS-induced modification of inappropriate interhemispheric inhibition.