Enhanced motor learning with bilateral transcranial direct current stimulation: Impact of polarity or current flow direction?

• Published in: Clinical neurophysiology Vol. 127; no. 4; pp. 2119 - 2126
• Main Authors: Naros, Georgios, Geyer, Marc, Koch, Susanne, Mayr, Lena, Ellinger, Tabea, Grimm, Florian, Gharabaghi, Alireza
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.04.2016
• Subjects: Adult; Current direction; Electrode montage; Evoked Potentials, Motor - physiology; Female; Functional Laterality - physiology; Hemispheric interaction; Humans; Learning - physiology; Male; Middle Aged; Motor Cortex - physiology; Neurology; Polarity; Proximal upper limb muscles; Psychomotor Performance - physiology; Robotic rehabilitation; Transcranial direct current stimulation; Transcranial Direct Current Stimulation - methods; Young Adult; M1; TDCS; a-TDCS; Transcranial direct current stimulation; SD; Hemispheric interaction; Robotic rehabilitation; Proximal upper limb muscles; ds-TDCS; Electrode montage; RF; bi-TDCS; Current direction; MEP; Polarity; LF; c-TDCS; TMS; motor-evoked potential; transcranial magnetic stimulation; transcranial direct current stimulation; cathodal transcranial direct current stimulation; primary motor cortex; double source transcranial direct current stimulation; right forehead; left forehead; bilateral transcranial direct current stimulation; anodal transcranial direct current stimulation; standard deviation
• ISSN: 1388-2457; 1872-8952; 1872-8952
• DOI: 10.1016/j.clinph.2015.12.020

•Systematic evaluation of stimulation polarity and current flow direction in bilateral TDCS on motor learning of proximal upper limb muscles in healthy subjects.•Bilateral TDCS induced larger effects than unilateral stimulation on task performance.•The effects of stimulation polarity were more pronounced than those of current flow direction. Bilateral transcranial direct current stimulation (TDCS) is superior to unilateral TDCS when targeting motor learning. This effect could be related to either the current flow direction or additive polarity-specific effects on each hemisphere. This sham-controlled randomized study included fifty right-handed healthy subjects in a parallel-group design who performed an exoskeleton-based motor task of the proximal left arm on three consecutive days. Prior to training, we applied either sham, right anodal (a-TDCS), left cathodal (c-TDCS), concurrent a-TDCS and c-TDCS with two independent current sources and return electrodes (double source (ds)-TDCS) or classical bilateral stimulation (bi-TDCS). Motor performance improved over time for both unilateral (a-TDCS, c-TDCS) and bilateral (bi-TDCS, ds-TDCS) TDCS montages. However, only the two bilateral paradigms led to an improvement of the final motor performance at the end of the training period as compared to the sham condition. There was no difference between the two bilateral stimulation conditions (bi-TDCS, ds-TDCS). Bilateral TDCS is more effective than unilateral stimulation due to its polarity-specific effects on each hemisphere rather than due to its current flow direction. This study is the first systematic evaluation of stimulation polarity and current flow direction of bi-hemispheric motor cortex TDCS on motor learning of proximal upper limb muscles.