Cerebellar direct current stimulation enhances on-line motor skill acquisition through an effect on accuracy.

The cerebellum is involved in the update of motor commands during error-dependent learning. Transcranial direct current stimulation (tDCS), a form of noninvasive brain stimulation, has been shown to increase cerebellar excitability and improve learning in motor adaptation tasks. Although cerebellar involvement has been clearly demonstrated in adaptation paradigms, a type of task that heavily relies on error-dependent motor learning mechanisms, its role during motor skill learning, a behavior that likely involves error-dependent as well as reinforcement and strategic mechanisms, is not completely understood. Here, in humans, we delivered cerebellar tDCS to modulate its activity during novel motor skill training over the course of 3 d and assessed gains during training (on-line effects), between days (off-line effects), and overall improvement. We found that excitatory anodal tDCS applied over the cerebellum increased skill learning relative to sham and cathodal tDCS specifically by increasing on-line rather than off-line learning. Moreover, the larger skill improvement in the anodal group was predominantly mediated by reductions in error rate rather than changes in movement time. These results have important implications for using cerebellar tDCS as an intervention to speed up motor skill acquisition and to improve motor skill accuracy, as well as to further our understanding of cerebellar function.

Variable Neural Contributions to Explicit and Implicit Learning During Visuomotor Adaptation.

We routinely make fine motor adjustments to maintain optimal motor performance. These adaptations have been attributed to both implicit, error-based mechanisms, and explicit, strategy-based mechanisms. However, little is known about the neural basis of implicit vs. explicit learning. Here, we aimed to use anodal transcranial direct current stimulation (tDCS) to probe the relationship between different brain regions and learning mechanisms during a visuomotor adaptation task in humans. We hypothesized that anodal tDCS over the cerebellum (CB) should increase implicit learning while anodal tDCS over the dorsolateral prefrontal cortex (dlPFC), a region associated with higher-level cognition, should facilitate explicit learning. Using a horizontal visuomotor adaptation task that measures explicit/implicit contributions to learning (Taylor et al., 2014), we found that dlPFC stimulation significantly improved performance compared to the other groups, and weakly increased explicit learning. However, CB stimulation had no effects on either target error or implicit learning. Previous work showed variable CB stimulation effects only on a vertical visuomotor adaptation task (Jalali et al., 2017), so in Experiment 2, we conducted the same study using a vertical context to see if we could find effects of CB stimulation. We found only weak effects of CB stimulation on target error and implicit learning, and now the dlPFC effect did not replicate. To resolve this discrepancy, in Experiment 3, we examined the effect of context (vertical vs. horizontal) on implicit and explicit contributions and found that individuals performed significantly worse and used greater implicit learning in the vertical screen condition compared to the horizontal screen condition. Across all experiments, however, there was high inter-individual variability, with strong influences of a few individuals, suggesting that these effects are not consistent across individuals. Overall, this work provides preliminary support for the idea that different neural regions can be engaged to improve visuomotor adaptation, but shows that each region's effects are highly context-dependent and not clearly dissociable from one another. This holds implications especially in neurorehabilitation, where an intact neural region could be engaged to potentially compensate if another region is impaired. Future work should examine factors influencing interindividual variability during these processes.

Adapted Resistance Training Improves Strength in Eight Weeks in Individuals with Multiple Sclerosis.

Hip weakness is a common symptom affecting walking ability in people with multiple sclerosis (MS). It is known that resistance strength training (RST) can improve strength in individuals with MS, however; it remains unclear the duration of RST that is needed to make strength gains and how to adapt hip strengthening exercises for individuals of varying strength using only resistance bands. This paper describes the methodology to set up and implement an adapted resistance strength training program, using resistance bands, for individuals with MS. Directions for pre- and post-strength tests to evaluate efficacy of the strength-training program are included. Safety features and detailed instructions outline the weekly program content and progression. Current evidence is presented showing that significant strength gains can be made within 8 weeks of starting a RST program. Evidence is also presented showing that resistance strength training can be successfully adapted for individuals with MS of varying strength with little equipment.