Cerebellar Transcranial Direct Current Stimulation for Motor Skill Acquisition in a Throwing Task
Creators: name: Jackson, Austuny 
Publisher: name: University of Nevada, Las Vegas
Year: 2016

description: Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique in which a very weak electrical current is applied to the scalp to either increase (anodal stimulation) or decrease (cathodal stimulation) the excitability of a selected brain region, most commonly the motor cortex. tDCS is a promising intervention that can modulate cortical excitability, enhance motor learning, and improve motor function in healthy subjects, older adults, stroke patients, Parkinson's disease, and in other cognitive and motor disorders. Recently, cerebellar transcranial direct current stimulation (c-tDCS) has started to be examined using similar protocols as existing ones used in studies of tDCS applied to the motor cortex and has been able to improve performance in simple arm movement tasks in young and old adults. This study was is set out to evaluate the influence that c-tDCS has on accuracy and variability of a complex, multi-joint throwing task in younger adult population. A total of 24 (n = 12 per group) healthy young adult males were allocated to either a c-tDCS group or a SHAM stimulation group. Each subject participated in two experimental sessions (practice session, retention session) performed on consecutive days. In the first session (practice session), subjects performed the throwing task in a baseline testing block, followed by 6 practice trial blocks. The practice blocks were followed by a post-testing block. For the practice blocks only, subjects performed the throwing task for 25 minutes in combination with either c-tDCS or SHAM stimulation. In the second session (retention session), subjects perform a retention test (1 block of trials of the throwing task) 24 hours after the practice session to quantify the magnitude of motor learning experienced by the two groups. 
The primary dependent variable was the endpoint error, whereas the endpoint variance was selected as the secondary dependent variable. For the test blocks, the dependent variables were analyzed by two-factor repeated measures ANOVAs: 2 Group (c-tDCS, SHAM) x 3 Test (BASELINE, POST, RETENTION). For the practice blocks, the dependent variables were analyzed by two-factor repeated measures ANOVAs: 2 Group (c-tDCS, SHAM) x 6 Block (1, 2, 3, 4, 5, 6). For the endpoint error in the test blocks, there were no significant differences between the two groups of subjects for any of the testing blocks. However, independent of group, endpoint error was significantly lower for the post-test block compared with the baseline test block (P = 0.004). Furthermore, endpoint error was similar between the retention test block and the baseline test block. Finally, the difference in endpoint error between the retention test block and the post-test block barely failed statistical significance (P = 0.063). For the practice blocks, the results indicated that there were no significant differences in endpoint error between the c-tDCS and SHAM groups (P = 0.148). Furthermore, endpoint error was not different for any of the practice blocks, which indicated that endpoint error did not decrease significantly with practice. For the endpoint variance in the test blocks, there was a significant (P = 0.034) GROUP x TEST interaction. Conversely, the post hoc analysis shows that the interaction came close, but missed statistical significance (P = 0.107 and P = 0.067) for lower endpoint variance in the c-tDCS group compared with the SHAM group for the post test block and retention test block, respectively. However, the difference between the groups for the baseline test was not significant (P = 0.824). For endpoint variance in the practice blocks, the results indicated that there were no significant differences between the c-tDCS and SHAM groups (P = 0.152). Furthermore, endpoint variance was not different for any of the practice blocks, which indicated that endpoint variance did not decrease significantly with practice. The data suggest that a one time acute application of c-tDCS does not improve the motor skill acquisition or retention in a complex, multi-joint throwing task in young adults compared to practice alone (SHAM stimulation).