Abstract
Transcranial direct current stimulation (tDCS) and transcranial random noise stimulation (tRNS) consist in the application of electrical current of small intensity through the scalp, able to modulate perceptual and motor learning, probably by changing brain excitability. We investigated the effects of these transcranial electrical stimulation techniques in the early and later stages of visuomotor learning, as well as associated brain activity changes using functional magnetic resonance imaging (fMRI). We applied anodal and cathodal tDCS, low-frequency and high-frequency tRNS (lf-tRNS, 0.1–100 Hz; hf-tRNS 101–640 Hz, respectively) and sham stimulation over the primary motor cortex (M1) during the first 10 minutes of a visuomotor learning paradigm and measured performance changes for 20 minutes after stimulation ceased. Functional imaging scans were acquired throughout the whole experiment. Cathodal tDCS and hf-tRNS showed a tendency to improve and lf-tRNS to hinder early learning during stimulation, an effect that remained for 20 minutes after cessation of stimulation in the late learning phase. Motor learning-related activity decreased in several regions as reported previously, however, there was no significant modulation of brain activity by tDCS. In opposition to this, hf-tRNS was associated with reduced motor task-related-activity bilaterally in the frontal cortex and precuneous, probably due to interaction with ongoing neuronal oscillations. This result highlights the potential of lf-tRNS and hf-tRNS to differentially modulate visuomotor learning and advances our knowledge on neuroplasticity induction approaches combined with functional imaging methods.
Highlights
The acquisition of a new motor skill follows a time-course that can be divided in two stages
There was a tendency for higher tracking error with lf-transcranial random noise stimulation (tRNS) and lower tracking error with cathodal Transcranial direct current stimulation (tDCS) and high-frequency tRNS (hf-tRNS), there was no significant effect of stimulation (F = 1,464; df = 4; p = 0,115) or interaction of block and stimulation (F = 0,641; df = 116; p = 0,999)
We investigated the effect of tDCS and tRNS on visuomotor learning using a task that requires subjects to learn a continuous pattern of pressure applied with right hand in response to a visual cue
Summary
The acquisition of a new motor skill follows a time-course that can be divided in two stages. The early stage is characterized by a marked improvement in performance in a relatively short period of time, followed by further progress in a gradual manner. This process is reflected in the dynamics of brain activity which can be observed regionally and as connectivity changes using fMRI [1,2,3,4,5]. The application of 10 minutes anodal tDCS over the primary motor cortex (M1) is followed by an increase and cathodal by a decrease in excitability, which can last for up to 90 min [6,7]. In addition to the modulation of cortical excitability, it has been shown that the effects of tDCS have functional repercussions at a perceptual [8,9], cognitive [10,11,12] and motor level [9,13,14]
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