Reversed Polarity bi-tDCS over M1 during a Five Days Motor Task Training Did Not Influence Motor Learning. A Triple-Blind Clinical Trial

Abstract

Transcranial direct current stimulation (tDCS) has been investigated as a way of improving motor learning. Our purpose was to explore the reversal bilateral tDCS effects on manual dexterity training, during five days, with the retention component measured after 5 days to determine whether somatosensory effects were produced. In this randomized, triple-blind clinical trial, 28 healthy subjects (14 women) were recruited and randomized into tDCS and placebo groups, although only 23 participants (13 women) finished the complete protocol. Participants received the real or placebo treatment during five consecutive days, while performing a motor dexterity training program of 20 min. The motor dexterity and the sensitivity of the hand were assessed pre- and post-day 1, post 5 days of training, and 5 days after training concluded. Training improved motor dexterity, but tDCS only produced a tendency to improve retention. The intervention did not produce changes in the somatosensory variables assessed. Thus, reversal bi-tDCS had no effects during motor learning on healthy subjects, but it could favor the retention of the motor skills acquired. These results do not support the cooperative inter-hemispheric model.

Transcranial Direct Current Stimulation (tDCS) Effects on Quantitative Sensory Testing (QST) and Nociceptive Processing in Healthy Subjects: A Systematic Review and Meta-Analysis

“…Finally, 29 studies [5,9,17,[19][20][21][22][23][24][25][26][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] were included in the qualitative analysis, and 17 [5,9,17,[19][20][21]24,26,40,43,44,46,48,50,53,55,56] were included in the quantitative analysis, with a total of 700 subjects. The whole screening process is shown in the PRISMA flow diagram (Figure 1).…”

“…Among the selected studies, most of the studies applied a-tDCS over M1 [5,9,19,[21][22][23][24][25]40,[42][43][44][47][48][49][50][55][56][57], and other studies applied a-tDCS over DLPFC [9,22,26,43,47,[51][52][53][54], S1 [24,53], and SO [19]. Six studies applied c-tDCS over M1 [21,24,40,47,54,57], two over DLPFC [26,47], two over S1 [45,48], and one over ACC [17].…”

“…Regarding current density, five applied a current density of 0.028 mA/cm 2 [21,24,41,45], two applied 0.04 mA/cm 2 [19,44], nine applied 0.057 mA/cm 2 [5,25,26,40,46,47,50,57], and one applied 0.1 mA/cm 2 [53]; the rest of the studies did not report current density. Regarding stimulation time, one applied tDCS for 7 min [38], three for 10 min [23,52], five for 15 min [21,24,41,45,57], eighteen for 20 min [5,9,19,22,26,[42][43][44][47][48][49][50][51][53][54][55][56], and one for 40 min [46]. Most studies conducted single treatment sessions [5,17,19,21,23,25,26,…”

“…Regarding stimulation time, one applied tDCS for 7 min [38], three for 10 min [23,52], five for 15 min [21,24,41,45,57], eighteen for 20 min [5,9,19,22,26,[42][43][44][47][48][49][50][51][53][54][55][56], and one for 40 min [46]. Most studies conducted single treatment sessions [5,17,19,21,23,25,26,[40][41][42][43][45][46][47]50,52,[55][56][57], and the rest between three and five sessions [9,22,24,44,51,…”

“…Regarding outcome measures, 12 measured PPTs [9,17,19,[21][22][23]41,44,45,48,52,53,55], 13 measured VAS or NRS [5,21,24,40,43,46,47,49,51,54,56], 10 measured HPTs [5,9,17,21,24,26,40,41,45,48], and 13 measured CPTs [9,17,19,22,25,[41][42][43]45,[47][48][49]57].…”