An acute application of transcranial random noise stimulation does not enhance motor skill acquisition or retention in a golf putting task
Introduction
The use of non-invasive electrical brain stimulation techniques such as transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS), and transcranial random noise stimulation (tRNS) (Prichard et al., 2014, Saiote et al., 2013, Terney et al., 2008) as interventions to improve motor performance has been increasing rapidly over the past several years due to promising findings in the majority of initial studies (Buch et al., 2017). tDCS has been the most commonly used non-invasive brain stimulation technique in the literature and involves passing a constant direct current between two electrodes placed on the scalp to either increase (anodal stimulation) or decrease (cathodal stimulation) the excitability of a specific cortical region, usually primary motor cortex (M1) (Horvath et al., 2015, Stagg and Nitsche, 2011). However, anodal tDCS is primarily employed as it typically increases cortical excitability and motor function, whereas cathodal tDCS has shown opposite results or no effect on motor function (Buch et al., 2017, Stagg and Nitsche, 2011, Stagg et al., 2011). The majority of anodal tDCS studies have shown motor performance improvements of 10–15% during or shortly after a single application lasting 10–20 min when compared to practice alone (Buch et al., 2017). However, there is a need for additional development and an improved understanding of the parameters and type of stimulation that may promote motor skill acquisition and learning (Buch et al., 2017).
tRNS possesses many of the same features and methodological considerations as tDCS (Terney et al., 2008). However, there are also several important differences between the two techniques which could potentially influence behavioral and physiological outcomes. For example, the application of tDCS involves the delivery of a continuous current, whereas in tRNS the current is delivered in a random-noise fashion with the positive and negative current emanating from the same electrode (Terney et al., 2008). Most importantly, research suggests that tRNS may be able to increase cortical excitability and improve motor performance to similar or greater extents than tDCS. For example, tRNS applied to the M1 of young adults for 10 min led to a performance increase of about 10% in a serial reaction time task (sequence of finger presses) and large increases (∼50–75%) in cortical excitability (Terney et al., 2008). This increase in cortical excitability is greater than the average increase of ∼30% seen after tDCS (Horvath et al., 2015). In addition, the physiological mechanisms mediating these enhancements in performance and cortical excitability may differ between the two methods. Specifically, tDCS may involve the modulation of NMDA receptors (Stagg & Nitsche, 2011), as well as GABAergic (Buch et al., 2017, Stagg and Nitsche, 2011, Stagg et al., 2009) and glutamatergic synapses (Stagg & Nitsche, 2011). In contrast, tRNS may be primarily associated with repetitive, more frequent activation of sodium channels (Antal and Herrmann, 2016, Terney et al., 2008), which could underlie the observed greater increases in cortical excitability with tRNS compared to tDCS and potentially greater enhancements in motor function (Prichard et al., 2014, Terney et al., 2008). tRNS also possesses a few other potential advantages compared to tDCS such as a lack of polarity specific effects, less skin irritation, and a greater ability to blind subjects with SHAM stimulation (Terney et al., 2008).
Taken together, these behavioral and physiological effects of tRNS have important implications for enhancing performance in healthy individuals, older adults, and especially in patients with movement disorders. Accordingly, each of the six available studies that have measured the effects of tRNS on cortical excitability has found significant increases (Chaieb et al., 2015, Chaieb et al., 2011, Laczo et al., 2014, Moliadze et al., 2010, Moliadze et al., 2014, Terney et al., 2008), whereas two of the three studies involving tRNS and motor tasks have produced performance enhancements (Saiote et al., 2013, Terney et al., 2008). Despite the promising findings of these tRNS studies, they all involved simple motor tasks such as the serial reaction time task (Terney et al., 2008), a pinch grip task (Saiote et al., 2013), and a tracing task performed with a stylus by the left hand (Prichard et al., 2014). It is currently unknown if tRNS can improve motor performance in a complex, multi-joint task involving coordination of the whole body, which would be more applicable to activities of daily living, occupational requirements, and physical activities.
The purpose of the present study was to determine the influence of tRNS on motor skill acquisition and retention in a golf putting task in young adults. Based on tRNS studies in relatively simple motor tasks (Prichard et al., 2014, Terney et al., 2008), it was hypothesized that tRNS would increase accuracy and reduce performance variability to a greater extent than practice alone in a complex golf putting task. Specifically, it was hypothesized that motor skill acquisition would be greater in the tRNS group compared to the SHAM group over the course of the practice blocks. Finally, it was expected that the degree of motor learning exhibited in the retention test would be greater in the tRNS group compared to the SHAM group.
Section snippets
Participants
A total of 34 males were recruited for the study (mean age: 23.1 ± 2.8; range: 18–30 years) by means of recruitment flyers posted in buildings on campus. The primary reason we only used male participants was to possibly reduce the variability of the data. Since the task was more complex than most motor tasks done in currently available tDCS studies, it was assumed that the inter-individual variability could, at least potentially, be greater for the current task. Thus, we chose to reduce a
Test blocks
For endpoint error, there was no main effect for group as the endpoint error was similar for the tRNS and SHAM groups when averaged over the three test blocks (F[1, 32] = 0.272, P = 0.606; Fig. 2A). However, there was a significant main effect for test (F[2, 64] = 16.528, P = 0.001) and post hoc analyses indicated that the endpoint error was greater for the baseline test block compared with the post test and retention (P = 0.001 and 0.012, respectively). Finally, the group × test interaction
Discussion
The purpose of the study was to determine the influence of tRNS on motor skill acquisition and retention in a golf putting task in young adults. The study produced three main findings. First, golf putting accuracy improved with practice, but the magnitude of motor skill acquisition was not different between the tRNS and SHAM groups. Second, golf putting performance variability improved with practice, but the reduction in endpoint variability was also similar for the tRNS and SHAM groups. Third,
Acknowledgements
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. The authors would like to thank Dr. Sheniz Moonie for assistance with the cluster analysis. The author Albuquerque LL was financially supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES).
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