Abstract
Due to the potential of anodal transcranial direct current stimulation (a-tDCS) for enhancement of fine sequenced movements and increasing interest in achieving high level of fine movements in the trained and untrained hands especially at initial stage of learning, we designed this study to investigate whether the application of single-session a-tDCS with small-size stimulating electrodes over FPN sites, such as dorsolateral prefrontal cortex (DLPFC), primary motor cortex (M1) or posterior parietal cortex (PPC) could enhance sequence learning with the trained hand and these effects are transferred into the untrained hand or not. A total of 51 right-handed healthy participants were randomly assigned to one of the four stimulation groups: a-tDCS of left M1, DLPFC, PPC, or sham. Stimulation was applied for 20 min during a sequential visual isometric pinch task (SVIPT). Eight blocks of training using SVIPT were completed with the right hand during stimulation. Two blocks of sequence training with each hand were performed by participants as assessment blocks at three time points: baseline, 15 min and one day following the intervention. Behavioral outcomes including movement time, error rate and skill were assessed in all assessment blocks across three time points. We also measured corticospinal excitability, short-interval intracortical inhibition, and intracortical facilitation using single- and paired-pulse transcranial magnetic stimulation. The results indicated that the behavioral outcomes were significantly improved with the right trained hand, but this learning effect was not modulated by a-tDCS with small-size stimulating electrodes over the FPN. Transfer of learning into the untrained hand was observed in all four groups for movement time but not for the error rate or skill. Our results suggest that sequential learning in SVIPT and its transfer into the untrained hand were not sensitive to a single-session a-tDCS with small-size stimulating electrodes over left M1, DLPFC or PPC in young healthy participants.
Highlights
Learning sequences in fine movements plays a crucial role in everyday life and requires a strong coordination between visual and motor cortex
Our findings showed no significant additional effects in implicit motor sequence learning in the trained hand following focal stimulation of anodal transcranial direct current stimulation (a-Transcranial Direct Current Stimulation (tDCS)) over any of the frontoparietal network (FPN) superficial sites compared to sham group
Our results indicated no changes in the excitability of M1 following a single session of a-tDCS over dorsolateral prefrontal cortex (DLPFC) or posterior parietal cortex (PPC) combined with training of sequential visual isometric pinch task (SVIPT)
Summary
Learning sequences in fine movements plays a crucial role in everyday life and requires a strong coordination between visual and motor cortex. A large body of neuroimaging evidence has revealed that sequence learning is mediated by frontoparietal network (FPN) superficial sites including dorsolateral prefrontal cortex (DLPFC) (Jenkins et al, 1994; Sakai et al, 1998; Miller and Cohen, 2001; Hasan et al, 2013), the primary motor cortex (M1) (Grafton et al, 1995; Karni et al, 1995; Hazeltine et al, 1997; Rioult-Pedotti et al, 2000) and posterior parietal cortex (PPC) (Jenkins et al, 1994; Sakai et al, 1998). M1 known to play an important role in acquisition and consolidation of movements, while rapid improvements gained over the course of a single training session (fast stage of learning) are more associated with the activity of DLPFC or PPC (Sakai et al, 1998; Koch et al, 2008a,b)
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