Cathodal transcutaneous spinal direct current stimulation (tsDCS) improves motor unit recruitment in healthy subjects

• Published in: Neuroscience letters Vol. 578; pp. 75 - 79
• Main Authors: Bocci, Tommaso, Vannini, Beatrice, Torzini, Antonio, Mazzatenta, Andrea, Vergari, Maurizio, Cogiamanian, Filippo, Priori, Alberto, Sartucci, Ferdinando
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier Ireland Ltd 22.08.2014
• Subjects: Adult; Cervical Vertebrae; Electrodes; Female; Humans; Male; Motor system; Motor unit number estimation; Motor unit recruitment; Motorneuron excitability; Recruitment, Neurophysiological; Spinal Cord - physiology; Thoracic Vertebrae; Transcutaneous Electric Nerve Stimulation; Transcutaneous spinal direct current stimulation; tsDCS; Young Adult; Transcutaneous spinal direct current stimulation; Motor unit recruitment; Motor unit number estimation; Motorneuron excitability; tsDCS; Motor system
• ISSN: 0304-3940; 1872-7972; 1872-7972
• DOI: 10.1016/j.neulet.2014.06.037

•We studied the effects of spinal direct current stimulation on motor unit recruitment.•Cathodal tsDCS improves motor unit recruitment and shortens peripheral silent period.•Anodal and sham tsDCS have no significant effect.•tsDCS could provide a novel therapeutic tool for several diseases characterized by abnormal motor unit recruitment.•tsDCS could also modulate supraspinal activities in a polarity-specific manner. Transcutaneous spinal direct current stimulation (tsDCS) is a new promising technique for modulating spinal cord function in humans. However, its effects on corticospinal pathways and lower motorneuron excitability are poorly understood. We studied the effects of tsDCS on motor unit recruitment by evaluating changes in motor unit number (MUNE) and peripheral silent period (PSP) after sham (s-tsDCS), anodal (a-tsDCS) and cathodal (c-tsDCS) tsDCS applied either over the cervical or the lower thoracic spinal cord in healthy subjects. For the calculation of MUNE we used the multipoint incremental technique recording from either the ulnar nerve innervated abductor digiti minimi (ADM) or the median nerve innervated abductor pollicis brevis (APB) muscle. c-tsDCS dramatically increases MUNE values following cervical polarization, while sham and anodal polarization have no significant effect (APB: F(4,99)=26.4, p<0.001, two-way repeated measures ANOVA with “time” and “stimulation” as factors; ADM: F(4,99)=22.1, p<0.0001). At the same time, c-tsDCS dampened PSP respect to sham and anodal conditions (p<0.0001). Interestingly, also thoracic c-tsDCS significantly improved motor unit recruitment compared with both s-tsDCS and a-tsDCS (APB: F(4,99)=20.1, p<0.0001; ADM: F(4,99)=16.6, p<0.0001). Our data in healthy subjects suggest that tsDCS, possibly also through supraspinal effects, could provide a novel therapeutic tool in managing several pathological conditions characterized by reduced motor unit recruitment, such as stroke and spinal cord injuries.