Noninvasive Spinal Cord Stimulation: Technical Aspects and Therapeutic Applications.

Background Electrical and magnetic trans-spinal stimulation can be used to increase the motor output of multiple spinal segments and modulate cortico-spinal excitability. The application of direct current through the scalp as well as repetitive transcranial magnetic stimulation are known to influence brain excitability, and hence can also modulate other central nervous system structures, including spinal cord. Objective This study aimed to evaluate the effects and the therapeutic usefulness of these noninvasive neuromodulatory techniques in healthy subjects and in the neurorehabilitation of patients with spinal cord disorders, as well as to discuss the possible mechanisms of action. A comprehensive review that summarizes previous studies using noninvasive spinal cord stimulation is lacking. Methods PubMed (MEDLINE) and EMBASE were systematically searched to identify the most relevant published studies. We performed here an extensive review in this field. Results By decreasing the spinal reflex excitability, electrical and magnetic trans-spinal stimulation could be helpful in normalizing reflex hyperexcitability and treating hypertonia in subjects with lesions to upper motor neurons. Transcutaneous spinal direct current stimulation, based on applying direct current through the skin, influences the ascending and descending spinal pathways as well as spinal reflex excitability, and there is increasing evidence that it also can induce prolonged functional neuroplastic changes. When delivered repetitively, magnetic stimulation could also modulate spinal cord functions; however, at present only a few studies have documented spastic-reducing effects induced by repetitive spinal magnetic stimulation. Moreover, paired peripheral and transcranial stimulation can be used to target the spinal cord and may have potential for neuromodulation in spinal cord-injured subjects. Conclusions Noninvasive electrical and magnetic spinal stimulation may provide reliable means to characterize important neurophysiologic and pathophysiologic aspects of spinal cord function. Moreover, transcutaneous direct current stimulation and repetitive magnetic stimulation may hold therapeutic promise in patients with spinal cord disorders, although future well-controlled studies are needed to corroborate and extend the preliminary findings.