Abstract
Background: Since motor learning is a key component for stroke recovery, enhancing motor skill learning is a crucial challenge for neurorehabilitation. Transcranial direct current stimulation (tDCS) is a promising approach for improving motor learning. The aim of this trial was to test the hypothesis that dual-tDCS applied bilaterally over the primary motor cortices (M1) improves online motor skill learning with the paretic hand and its long-term retention. Methods: Eighteen chronic stroke patients participated in a randomized, cross-over, placebo-controlled, double bind trial. During separate sessions, dual-tDCS or sham dual-tDCS was applied over 30 min while stroke patients learned a complex visuomotor skill with the paretic hand: using a computer mouse to move a pointer along a complex circuit as quickly and accurately as possible. A learning index involving the evolution of the speed/accuracy trade-off was calculated. Performance of the motor skill was measured at baseline, after intervention and 1 week later. Results: After sham dual-tDCS, eight patients showed performance worsening. In contrast, dual-tDCS enhanced the amount and speed of online motor skill learning compared to sham (p < 0.001) in all patients; this superiority was maintained throughout the hour following. The speed/accuracy trade-off was shifted more consistently after dual-tDCS (n = 10) than after sham (n = 3). More importantly, 1 week later, online enhancement under dual-tDCS had translated into superior long-term retention (+44%) compared to sham (+4%). The improvement generalized to a new untrained circuit and to digital dexterity. Conclusion: A single-session of dual-tDCS, applied while stroke patients trained with the paretic hand significantly enhanced online motor skill learning both quantitatively and qualitatively, leading to successful long-term retention and generalization. The combination of motor skill learning and dual-tDCS is promising for improving post-stroke neurorehabilitation.
Highlights
In the field of stroke neurorehabilitation, motor learning has recently become the focus of a great deal of attention
The main findings of this experiment were that 30 min of dualtDCS applied bilaterally over M1 in chronic stroke patients while they learned a complex motor skill with the paretic hand (i) rapidly and significantly enhanced online motor skill learning, (ii) enhanced the quality of motor skill learning by increasing the shift of the speed/accuracy trade-off, (iii) successfully translated online improvement into long-term retention of the motor skill, and (iv) induced a generalization of performance improvement to untrained tasks, such as digital dexterity and an alternative version of the motor skill
Potential confounding effects due to attention, fatigue, concentration, and blinding were not evaluated. We feel it unlikely that such non-specific effects might by themselves explain the intensity and nature of the improvements observed in motor skill learning, given the localization of the electrodes and the demonstration that blinding with sham Transcranial direct current stimulation (tDCS) is efficient (Gandiga et al, 2006). This is the first demonstration that a single-session of dual-tDCS applied during training dramatically enhanced online motor skill learning with the paretic hand in stroke patients, which translated into successful long-term retention of the motor skill
Summary
In the field of stroke neurorehabilitation, motor learning has recently become the focus of a great deal of attention. Motor skill learning is defined as a training-induced improvement in motor performance characterized by a shift in the speed/accuracy trade-off that persists over time (Reis et al, 2009; Dayan and Cohen, 2011; Krakauer and Mazzoni, 2011). Transcranial direct current stimulation (tDCS) is a promising approach for improving motor learning The aim of this trial was to test the hypothesis that dual-tDCS applied bilaterally over the primary motor cortices (M1) improves online motor skill learning with the paretic hand and its long-term retention. 1 week later, online enhancement under dual-tDCS had translated into superior long-term retention (+44%) compared to sham (+4%). Conclusion: A single-session of dualtDCS, applied while stroke patients trained with the paretic hand significantly enhanced online motor skill learning both quantitatively and qualitatively, leading to successful longterm retention and generalization. The combination of motor skill learning and dual-tDCS is promising for improving post-stroke neurorehabilitation
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