The Influence Of Transcranial Random Noise Stimulation On Motor Skill Acquisition And Learning In A Modified Golf Putting Task

Transcranial random noise stimulation (tRNS) is a form of non-invasive brain stimulation (NIBS) that has been shown to increase motor performance in simple motor tasks. The purpose of the present study was to determine the influence of tRNS on motor skill acquisition and learning in a complex, modified golf putting task in young adults. Twenty-four (n = 12 per group) healthy young adult males were allocated to either a tRNS group or a SHAM stimulation group. Both groups performed 6 trials of the golf putting task in a baseline testing block, followed by 4 practice blocks of 15 trials. The practice blocks were followed by a post-testing block (6 trials) that was performed five minutes after the last practice block, and a retention testing block (6 trials) that was performed 24 hours later. For the practice blocks, subjects performed the golf putting task for 20 minutes in combination with either tRNS or SHAM stimulation. tRNS or SHAM stimulation was applied to the motor cortex with the stimulating electrode centered over the motor hotspot of the first dorsal interosseous muscle. The primary dependent variables were endpoint error and endpoint variance, whereas the putter face angle relative to ball path at impact and forward swing time were selected as secondary dependent variables. For the practice blocks, the dependent variables were analyzed by two-factor repeated measures ANOVAs: 2 group (real tRNS, SHAM) x 4 Block. For the testing blocks, the dependent variables were analyzed by two-factor repeated measures ANOVAs: 2 group (real tRNS, SHAM) x 3 Test (BASELINE, POST and RETENTION). The results indicted that there were no significant differences in endpoint error or endpoint variance between the tRNS and SHAM groups for the practice blocks. However, there was a significant reduction in endpoint error between blocks 1 and 3 (P = 0.20), and a significant reduction in endpoint variance between blocks 1 and 3, and 1 and 4 (P = 0.011 and 0.039, respectively). For face angle relative to path, there was a iv significant group x block interaction, but the post-hoc tests failed statistical significance. Forward swing time remained invariant across all of the practice blocks. For the testing blocks, endpoint error was significantly reduced in both groups between the baseline block and the post-test block (P = 0.000), but there was no difference between groups. Similarly, endpoint variance was not different between groups, but decreased significantly for both groups between the baseline block and the post-test block, and between the baseline block and retention block (P = 0.000 and 0.018, respectively). Face angle relative to path was significantly more closed for both groups in the post-test block comparison to the baseline block (P = 0.012) and more opened in the retention block when compared to post-test block (P = 0.028). Forward swing time was not different between groups or between any of the testing blocks. These findings suggest that tRNS influenced the execution of this motor task, but this influence did not occur in a manner that lead to an improvement in motor skill acquisition or motor learning in the current task conditions

The Influence of Cerebellar Transcranial Direct Current Stimulation on Motor Function in Parkinson’s Disease

Parkinson\u27s disease (PD) is the most common movement disorder and the second most common neurodegenerative disorder. PD is characterized by dopaminergic cell loss in the substantia nigra pars compacta, which leads to a reduction in dopamine in the striatum. These physiological mechanisms lead to a number of motor impairments such as bradykinesia, rigidity, tremor, and postural instability that severely limit the ability of individuals with PD to perform many essential daily living activities. Although current pharmacological, surgical, and physical exercise treatment approaches are valuable they are either only mildly effective, expensive, or associated with a variety of side effects. Therefore, development of new adjunct interventions that are effective and have a realistic potential to be implemented into clinical practice would be highly beneficial. The current pharmaceutical, surgical, and management strategies for PD are directed towards relieving the symptoms associated with PD. Levodopa combined with other medications represents the standard treatment for PD, but their efficacy diminishes over time and leads to side effects such as dyskinesia. For advanced PD, deep brain stimulation is the established surgical approach and can improve motor function and quality of life. Nonetheless, deep brain stimulation is associated with surgical contraindications, high costs, neuropsychiatric side effects, and is not effective in treating non-motor PD symptoms. Physical exercise is also commonly prescribed in PD primarily based on animal studies, but the magnitude of these positive effects has generally not been achieved in humans. However, not all patients have the ability, financial resources, available facilities, or determination to engage in long-term high intensity exercise programs to realize their benefit. While several forms of exercise can induce clinically significant motor improvements in PD, the most successful strategy to improve motor function would likely entail pairing adjunctive therapies with rehabilitation to enhance or complement the effects of exercise. Non-invasive brain stimulation methods such as repetitive transcranial magnetic stimulation (rTMS) have shown promise in alleviating PD symptoms, but practical limitations as well as inconsistent or mild positive effects limit its clinical applicability. Recently, transcranial direct current stimulation (tDCS) has emerged as a powerful brain stimulation technique that can enhance motor performance and cortical function in PD. Most importantly, tDCS is now regarded to be a more effective form of non-invasive brain stimulation compared to rTMS in PD. In addition, tDCS offers several important advantages over rTMS such as portability, safety, ease of administration, ability to be delivered during motor activities, a superior ability to blind participants with SHAM stimulation, and low cost (as low as $400 versus$20,000-100,000 for rTMS). Taken together, these lines of reasoning strongly suggest that tDCS may represent such an intervention with a realistic potential to be translated into clinical practice. Anodal tDCS of motor cortex (M1) improves motor performance in young adults, older adults, stroke, and in PD. This involves passing a current over M1 through surface electrodes, which increases M1 excitability for ~90 minutes. Accordingly, most M1-tDCS studies have found improvements in motor performance of approximately 10-15% during or after a single 10-20 minute session when compared to motor practice alone in young adults and old adults as well as in PD. Most importantly, longer-term studies lasting between 3 days and 2 weeks have documented that these improvements in performance can be increased to up about 20-30% compared to a single M1-tDCS session in healthy adults and in one notable study in PD. Despite these positive findings involving M1-tDCS in PD, development of new non-invasive brain stimulation techniques or the targeting of additional brain areas could provide additional avenues to improve motor function in PD. Recently, tDCS delivered to the cerebellum (c-tDCS) has also been reported to significantly improve motor skill in young and old adults. The ability of c-tDCS to impact motor skill learning in older adults is particularly interesting because accumulating evidence suggests that the cerebellum may be the primary brain area responsible for the movement impairments often observed in by older adults. Similarly, the cerebellum has recently been implicated in contributing to the motor deficits associated with PD. Despite these observations, no studies have examined the influence of c-tDCS on motor learning in PD, given that most individuals with PD are older adults. The M1 projections to upper limb motor neurons play a predominant role in the generation and execution of skilled movements. However, M1 output depends on inputs from sources such as premotor cortex, contralateral M1, and basal ganglia along with crucial contributions from cerebellum, which is strongly involved in movement timing, multi-joint coordination, agonist and antagonist muscle interactions, and error detection in goal-directed movements. Although PD is primarily a basal ganglia disorder, the widespread cerebellar involvement in PD pathophysiology based on mounting anatomical, physiological, and clinical evidence forms the basis for targeting it with c-tDCS. In addition, more specific evidence provides further rationale for c-tDCS in PD treatment: 1) previously unknown bi-directional pathways have recently been discovered between basal ganglia and cerebellum and M1-tDCS has been shown in animal and human physiological studies to induce remote effects in anatomically interconnected CNS regions (basal ganglia, thalamus, pain centers, spinal cord). For example, M1-tDCS increased striatal extracellular dopamine levels in rats and improved their motor function. The evidence for tDCS remote effects provides support for the idea that c-tDCS may indirectly impact basal ganglia in PD; 2) impaired cerebellar function in PD may be a compensatory mechanism that attempts to diminish the negative influences of abnormal basal ganglia activity as PD patients with greater cerebellar activity exhibit better motor function. Thus, c-tDCS may improve function by enhancing these compensatory processes by increasing cerebellar activity; 3) c-tDCS improves motor performance in young and older adults and tDCS of M1 improves performance in these populations and in PD; 4) tDCS efficacy scales with age and impairment level due to motor disorders making improvements in PD more likely to occur; and 5) c-tDCS led to greater improvements in an arm movement task compared to M1-tDCS in young adults. Collectively, these factors and the positive effects on motor performance obtained in several studies involving c-tDCS in young and older adults provide strong rationale for the investigation of c-tDCS for PD treatment. Despite these interrelated lines of reasoning, no studies have examined the influence of c-tDCS on motor performance in PD in either the short or long-term. Therefore, the overall purpose of this dissertation was to determine the influence of c-tDCS on motor skill acquisition, motor learning, and transfer of motor learning in PD. This was accomplished through a series of 3 interrelated studies. For the first study (Chapter 2), the primary purpose was to examine the influence of a single session of c-tDCS on motor performance in a complex, visuomotor isometric precision grip task (PGT) in PD. The secondary purpose was to determine the influence of c-tDCS on the transfer of motor performance in PD. Based on c-tDCS studies involving practice of hand and arm tasks in young and older adults and M1-tDCS studies in PD, it was hypothesized that c-tDCS would increase motor performance in the PGT and in the transfer tasks to a greater extent than SHAM stimulation in PD. Therefore, the major methodological aspects of study 1 that distinguished it from the subsequent studies included: 1) it involved acute application of c-tDCS in a single experimental session; 2) it utilized only one primary motor task that was performed concurrently with administration of c-tDCS; 3) it also investigated the influence of c-tDCS on transfer of motor performance to motor tasks not performed simultaneously with c-tDCS and not practiced extensively; and 4) all experimental testing was conducted while participants were off of their medications; and 5) it utilized a within-participants design. Therefore each participant underwent both the c-tDCS and SHAM conditions. The within-participants design was chosen in this study as it has the advantage of being able to minimize the possible inter-individual response to c-tDCS. The main findings of the study were that a single session of c-tDCS did not elicit improvements in motor performance or transfer of motor performance in hand and arm tasks in PD In the second study (Chapter 3), the purpose was to determine the effects of c-tDCS on motor performance in PD while participants were on medications. This was accomplished by having participants perform two motor tasks with their most affected hand in a baseline condition and in an experimental condition. Most importantly, one group of participants received c-tDCS during performance of the motor tasks in the experimental condition, whereas the other group received SHAM stimulation. The major methodological features of study 2 that distinguished it in most aspects from the two other studies included: 1) it involved acute application of c-tDCS in a single experimental session; 2) it comprised two different motor tasks that were performed concurrently with administration of c-tDCS; 3) it did not investigate the influence of c-tDCS on transfer of motor performance to untrained tasks; 4) all experimental testing was conducted while participants were on their medications; 5) it utilized a between-participants design. Thus, two groups of PD participants were utilized and allocated into either a c-tDCS or SHAM group. The main findings of the study were that a single session of c-tDCS did not elicit enhancements in motor performance in either of the hand and arm tasks performed concurrent with c-tDCS in PD. In the third study (Chapter 4), the primary purpose was to determine the influence of long-term application of c-tDCS on motor learning in PD. The secondary purpose was to examine the influence of long-term application of c-tDCS on transfer of motor learning in PD. This was accomplished by employing a long-term training study. Specifically, 9 practice sessions were performed over a 2 week period that involved extensive practice of an isometric pinch grip task (PGT) and a rapid arm movement task (AMT). These practice tasks were performed over a 25 minute period concurrent with either c-tDCS or SHAM stimulation. A set of transfer tasks that included clinical rating scales, manual dexterity tests, and lower extremity function assessments were quantified in test sessions at Baseline, 1, 14, and 28 days after the end of practice (EOP). Thus, the major methodological features of study 3 that distinguished it in most aspects from the two other studies included: 1) it involved chronic application of c-tDCS over 9 practice sessions and was concerned with the effect of c-tDCS on long-term motor learning; 2) it comprised two different motor tasks that were performed concurrently with administration of c-tDCS; 3) it investigated the influence of c-tDCS on transfer of motor learning to untrained tasks; 4) experimental testing was conducted while participants were both off and on their medications; 5) it utilized a between-participants design. Thus, participants were allocated into either a c-tDCS or SHAM group. The main findings of the study were that long-term application of c-tDCS concurrent with motor practice did not enhance motor learning to a greater extent than practice alone in PD. Similarly, long-term application of c-tDCS did not increase transfer of motor learning in PD. In summary, this dissertation examined the influence of c-tDCS on motor skill acquisition, motor learning, and transfer of motor learning in PD. Collectively, the findings provided no evidence that c-tDCS applied in either the short or the long-term is an effective intervention to improve motor function in PD

Cerebellar Transcranial Direct Current Stimulation Applied over Multiple Days Does Not Enhance Motor Learning of a Complex Overhand Throwing Task in Young Adults

Cerebellar transcranial direct current stimulation (tDCS) enhances motor skill and learning in relatively simple motor tasks, but it is unclear if c-tDCS can improve motor performance in complex motor tasks. The purpose of this study was to determine the influence of c-tDCS applied over multiple days on motor learning in a complex overhand throwing task. In a double-blind, randomized, between-subjects, SHAM-controlled, experimental design, 30 young adults were assigned to either a c-tDCS or a SHAM group. Participants completed three identical experiments on consecutive days that involved overhand throwing in a pre-test block, five practice blocks with concurrent c-tDCS, and a post-test block. Overhand throwing endpoint accuracy was quantified as the endpoint error. The first dorsal interosseous muscle motor evoked potential (MEP) amplitude elicited by transcranial magnetic stimulation was used to quantify primary motor cortex (M1) excitability modulations via c-tDCS. Endpoint error significantly decreased over the 3 days of practice, but the magnitude of decrease was not significantly different between the c-tDCS and SHAM group. Similarly, MEP amplitude slightly increased from the pre-tests to the post-tests, but these increases did not differ between groups. These results indicate that multi-day c-tDCS does not improve motor learning in an overhand throwing task or increase M1 excitability

Transcranial direct current stimulation of primary motor cortex over multiple days improves motor learning of a complex overhand throwing task

Transcranial direct current stimulation (tDCS) applied to the primary motor cortex (M1) improves motor learning in relatively simple motor tasks performed with the hand and arm. However, it is unknown if tDCS can improve motor learning in complex motor tasks involving whole-body coordination with significant endpoint accuracy requirements. The primary purpose was to determine the influence of tDCS on motor learning over multiple days in a complex over-hand throwing task. This study utilized a double-blind, randomized, SHAM-controlled, between-subjects experimental design. Forty-six young adults were allocated to either a tDCS group or a SHAM group and completed three experimental sessions on three consecutive days at the same time of day. Each experimental session was identical and consisted of overhand throwing trials to a target in a pre-test block, five practice blocks performed simultaneously with 20 min of tDCS, and a post-test block. Overhand throwing performance was quantified as the endpoint error. Transcranial magnetic stimulation was used to obtain motor-evoked potentials (MEPs) from the first dorsal interosseus muscle to quantify changes in M1 excitability due to tDCS. Endpoint error significantly decreased over the three days of practice in the tDCS group but not in the SHAM group. MEP amplitude significantly increased in the tDCS group, but the MEP increases were not associated with increases in motor learning. These findings indicate that tDCS applied over multiple days can improve motor learning in a complex motor tasks in healthy young adults

An Acute Application of Cerebellar Transcranial Direct Current Stimulation Does Not Improve Motor Performance in Parkinson’s Disease

Transcranial direct current stimulation of the cerebellum (c-tDCS) improves motor performance in young and old adults. Based on the cerebellar involvement in Parkinson’s disease (PD), c-tDCS could have potential to improve motor function in PD. The purpose was to determine the effects of c-tDCS on motor performance in PD while participants were on medications. The study was a randomized, double-blind, SHAM-controlled, between-subjects design. Twenty-two participants with PD were allocated to either a c-tDCS group or a SHAM group. All participants completed one experimental session and performed two motor tasks with their most affected hand in a Baseline condition (no stimulation) and an Experimental condition. The motor tasks were a visuomotor isometric precision grip task (PGT) and a rapid arm movement task (AMT). The primary dependent variables were force error and endpoint error in the PGT and AMT, respectively. There were no significant differences in force error or endpoint error in the Experimental condition between the c-tDCS and SHAM groups. These results indicate that an acute application of c-tDCS does not enhance motor performance in hand and arm tasks in PD. Longer-term c-tDCS application over multiple days may be needed to enhance motor function in PD

An Acute Application of Transcranial Random Noise Stimulation Does Not Enhance Motor Skill Acquisition or Retention in a Golf Putting Task

Transcranial random noise stimulation (tRNS) is a brain stimulation technique that has been shown to increase motor performance in simple motor tasks. The purpose was to determine the influence of tRNS on motor skill acquisition and retention in a complex golf putting task. Thirty-four young adults were randomly assigned to a tRNS group or a SHAM stimulation group. Each subject completed a practice session followed by a retention session. In the practice session, subjects performed golf putting trials in a baseline test block, four practice blocks, and a post test block. Twenty-four hours later subjects completed the retention test block. The golf putting task involved performing putts to a small target located 3 m away. tRNS or SHAM was applied during the practice blocks concurrently with the golf putting task. tRNS was applied over the first dorsal interosseus muscle representation area of the motor cortex for 20 min at a current strength of 2 mA. Endpoint error and endpoint variance were reduced across the both the practice blocks and the test blocks, but these reductions were not different between groups. These findings suggest that an acute application of tRNS failed to enhance skill acquisition or retention in a golf putting task

Increased interregional virus exchange and nucleotide diversity outline the expansion of chikungunya virus in Brazil

Abstract The emergence and reemergence of mosquito-borne diseases in Brazil such as yellow fever, zika, chikungunya, and dengue have had serious impacts on public health. Concerns have been raised due to the rapid dissemination of the chikungunya virus across the country since its first detection in 2014 in Northeast Brazil. In this work, we carried out on-site training activities in genomic surveillance in partnership with the National Network of Public Health Laboratories that have led to the generation of 422 chikungunya virus genomes from 12 Brazilian states over the past two years (2021–2022), a period that has seen more than 312 thousand chikungunya fever cases reported in the country. These genomes increased the amount of available data and allowed a more comprehensive characterization of the dispersal dynamics of the chikungunya virus East-Central-South-African lineage in Brazil. Tree branching patterns revealed the emergence and expansion of two distinct subclades. Phylogeographic analysis indicated that the northeast region has been the leading hub of virus spread towards other regions. Increased frequency of C > T transitions among the new genomes suggested that host restriction factors from the immune system such as ADAR and AID/APOBEC deaminases might be driving the genetic diversity of the chikungunya virus in Brazil