Abstract
BackgroundTranscranial direct current stimulation (tDCS) is a non-invasive technique that has been found to modulate the excitability of neurons in the brain. The polarity of the current applied to the scalp determines the effects of tDCS on the underlying tissue: anodal tDCS increases excitability, whereas cathodal tDCS decreases excitability. Research has shown that applying anodal tDCS to the non-dominant motor cortex can improve motor performance for the non-dominant hand, presumably by means of changes in synaptic plasticity between neurons. Our previous studies also suggest that applying cathodal tDCS over the dominant motor cortex can improve performance for the non-dominant hand; this effect may result from modulating inhibitory projections (interhemispheric inhibition) between the motor cortices of the two hemispheres. We hypothesized that stimultaneously applying cathodal tDCS over the dominant motor cortex and anodal tDCS over the non-dominant motor cortex would have a greater effect on finger sequence performance for the non-dominant hand, compared to stimulating only the non-dominant motor cortex. Sixteen right-handed participants underwent three stimulation conditions: 1) dual-hemisphere – with anodal tDCS over the non-dominant motor cortex, and cathodal tDCS over the dominant motor cortex, 2) uni-hemisphere – with anodal tDCS over the non-dominant motor cortex, and 3) sham tDCS. Participants performed a finger-sequencing task with the non-dominant hand before and after each stimulation. The dependent variable was the percentage of change in performance, comparing pre- and post-tDCS scores.ResultsA repeated measures ANOVA yielded a significant effect of tDCS condition (F(2,30) = 4.468, p = .037). Post-hoc analyses revealed that dual-hemisphere stimulation improved performance significantly more than both uni-hemisphere (p = .021) and sham stimulation (p = .041).ConclusionWe propose that simultaneously applying cathodal tDCS over the dominant motor cortex and anodal tDCS over the non-dominant motor cortex produced an additive effect, which facilitated motor performance in the non-dominant hand. These findings are relevant to motor skill learning and to research studies of motor recovery after stroke.
Highlights
Transcranial direct current stimulation is a non-invasive technique that has been found to modulate the excitability of neurons in the brain
We found that cathodal Transcranial Direct Current Stimulation (tDCS) over the dominant motor cortex had a facilitative effect for the non-dominant hand [4,12]; presumably, the cathodal tDCS modulated inhibitory projections between the motor cortices of the two brain hemispheres to achieve this effect
The significant effects were not due to differences in baseline scores across conditions; a one-way ANOVA with three levels comparing the number of points per trial at baseline yielded F(2,133) = .30, p = .75. These results show that dual-hemisphere stimulation improved motor performance for the left hand significantly more than both unihemisphere and sham stimulation
Summary
Transcranial direct current stimulation (tDCS) is a non-invasive technique that has been found to modulate the excitability of neurons in the brain. Research has shown that applying anodal tDCS to the non-dominant motor cortex can improve motor performance for the non-dominant hand, presumably by means of changes in synaptic plasticity between neurons. Our previous studies suggest that applying cathodal tDCS over the dominant motor cortex can improve performance for the non-dominant hand; this effect may result from modulating inhibitory projections (interhemispheric inhibition) between the motor cortices of the two hemispheres. Techniques that stimulate the brain non-invasively hold the promise of revealing causal relations between brain regions and brain functions [1] These techniques may facilitate skill acquisition, learning and neural plasticity [2,3,4]. It may be possible to improve motor ability by applying cathodal tDCS to the motor cortex ipsilateral to the performing hand; this may have a beneficial effect in stroke patients by diminishing maladaptive inhibitory projections from the undamaged hemisphere onto the damaged motor cortex [5,6,13,14,15]
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