Site‐specific effects of mental practice combined with transcranial direct current stimulation on motor learning

Abstract

Mental practice can induce significant neural plasticity and result in motor performance improvement if associated with motor imagery tasks. Given the effects of transcranial direct current stimulation (tDCS) on neuroplasticity, the current study tested whether tDCS, using different electrode montages, can increase the neuroplastic effects of mental imagery on motor learning. Eighteen healthy right-handed adults underwent a randomised sham-controlled crossover experiment to receive mental training combined with either sham or active anodal tDCS of the right primary motor cortex (M1), right supplementary motor area, right premotor area, right cerebellum or left dorsolateral prefrontal cortex (DLPFC). Motor performance was assessed by a blinded rater using: non-dominant handwriting time and legibility, and mentally trained task at baseline (pre) and immediately after (post) mental practice combined with tDCS. Active tDCS significantly enhances the motor-imagery-induced improvement in motor function as compared with sham tDCS. There was a specific effect for the site of stimulation such that effects were only observed after M1 and DLPFC stimulation during mental practice. These findings provide new insights into motor imagery training and point out that two cortical targets (M1 and DLPFC) are significantly associated with the neuroplastic effects of mental imagery on motor learning. Further studies should explore a similar paradigm in patients with brain lesions.

The Uncertain Outcome of Prefrontal tDCS

“…Was shown to decrease : a) working memory performance [36]; b) risk taking behaviors [37]; c) negative emotions perception [38-39]; d) categorization learning [28]); e) executive functioning performance only in a COMT Met-Met group (cognitive flexibility [40]). Was shown to increase : a) working memory performance [21,41-49]; b) positive emotion processing [50-52]; c) pain thresholds [53] ; d) performance on verbal tasks (verbal; word retrieval:[54]; word fluency:[18]); e) executive function performance (mental flexibility: [22]; inhibition: [46]; problem solving: [24,55-56]; planning [15]); f) control of negative emotions [39,57]; g) memory performance and learning [25,27,58-60]. Showed no significant effect on: a) mood [61].…”

tDCS over left M1 or DLPFC does not improve learning of a bimanual coordination task

“…However, other authors have argued for delivering stimulation during learning of a motor task50. Empirical evidence has provided strong support for the effects of tDCS both during8234051 and before a behavioural task4546525354, suggesting that online or offline stimulation protocols do not give different results. These results were further confirmed by a meta-analysis25.…”

“…The task enables us to systematically manipulate task difficulty by training subjects in various ratios of rotation frequency between the left and right hand: (a) an easy isofrequency ratio in which both hands rotate in the same frequency, and (b) more difficult multifrequency ratios in which one hand rotates faster than the other hand. Due to the complex nature of the task and earlier recommendations for multiple tDCS sessions over a single session293940 we trained our participants over multiple days (Day 1–4) with a retention test which was performed 7 days after the last day of training (Day 11). Furthermore, the multi day training is particularly useful to disentangle the effect of tDCS on two components of the learning process (i.e., acquisition and consolidation).…”

The impact of transcranial direct current stimulation (tDCS) combined with modified constraint-induced movement therapy (mCIMT) on upper limb function in chronic stroke: a double-blind randomized controlled trial

“…Some clinical trials using tDCS combined with different physical therapy approaches have supported this hypothesis [2][3][4][5].…”