Kim, Hakjoo (2018-12). The Effect of Timing of Anodal Transcranial Direct Current Stimulation (tDCS) on Online and Offline Motor Sequence Learning. Master's Thesis.
Transcranial direct current stimulation (tDCS) has emerged as a noninvasive brain stimulation technique that may facilitate the acquisition, consolidation, and long-term retention of motor skills. The present study aims to examine the effect of timing of anodal tDCS at primary motor cortex (M1) for online and offline changes in motor sequence learning. At this time, the extant literature provides some support for the efficacy of tDCS applied during motor training for increased online and offline gain in skill, while administration of exogenous stimulation before or after training provides no benefit beyond a sham stimulation control. Unfortunately, this conclusion is made on the basis of multiple cross-experiment comparisons within which tDCS was applied in very different ways (e.g., electrode montage, duration, current, etc.). The main hypothesis of the present study is that only application of anodal tDCS at M1, while also practicing a serial reaction time (SRT) task, will result in greater online and/or offline gains manifest as faster response times. Ninety right-handed undergraduate students participated in this study. They were randomly assigned to one of four tDCS condition groups: (1) tDCS before practice (BEF), (2) tDCS during practice (DUR), (3) tDCS after practice (AFT), and (4) no tDCS (NO) condition group. The non-dominant hand (left hand) was used to perform 15-min of practice with an SRT. Participants in the BEF condition group received 2-mA of bi-hemispheric tDCS over contralateral M1 before practice. tDCS was administered during the 15-min practice period for the DUR group. The AFT condition group received tDCS immediately after they finished practice. Participant assigned to the NO condition group did not receive tDCS and only performed the SRT task. The retention test was conducted 1 hr and 24 hr after the practice session was concluded. Online, offline, and total changes in response time were analyzed, and the results indicated that the online, offline, and total change in response time for the SRT between the four tDCS timing conditions was not different. These data question the effectiveness of a single dose of tDCS, regardless of its temporal placement relative to physical training, for inducing improvement in skill.