Effects of anodal tDCS over primary motor cortex on motor learning and brain activity

104 

Abstract Submission 

Tatsuya Miyazaki¹, Masaya Hirashima², Daichi Nozaki³, Hiroshi Kadota¹

¹Graduate School of Engineering, Kochi University of Technology, Kami, Kochi, ²CiNet, Advanced ICT Research Institute, NICT, Suita, Osaka, ³Graduate School of Education, University of Tokyo, Bunkyo-ku, Tokyo

Tatsuya Miyazaki  
Graduate School of Engineering, Kochi University of Technology
Kami, Kochi

Masaya Hirashima  
CiNet, Advanced ICT Research Institute, NICT
Suita, Osaka

Daichi Nozaki  
Graduate School of Education, University of Tokyo
Bunkyo-ku, Tokyo

Hiroshi Kadota  
Graduate School of Engineering, Kochi University of Technology
Kami, Kochi

Humans learn and improve various motor skills through repeated training in daily life. Transcranial direct current electrical stimulation (tDCS) during motor learning is a useful tool to promote and consolidate motor learning [1]. A previous study using tDCS during reaching tasks in a force field environment suggested that anodal stimulation of the primary motor cortex (M1) is involved in the acquisition of internal models [2]. However, changes in brain activity following brain stimulation have not yet been fully elucidated. Therefore, we investigated the effects of tDCS on task performance and brain activity using a reaching task in a force field environment and functional MRI (fMRI).

Thirty-two healthy right-handed adults (18–27 years old, 10 women) participated in this study. Four participants were excluded from the analysis because of poor image quality. This study was approved by the Ethics Committee of Kochi University of Technology. The participants manipulated the robotic device using right-wrist movements to move a cursor and perform a reaching task. Each set consisted of 60 trials and 10 sets were conducted. This experiment was divided into four segments: base segment (1 set), learning segment (3 sets), washout segment (3 sets), and recall segment (3 sets). Participants were trained in a velocity-dependent clockwise force field in the learning and recall segments. We acquired fMRI data for all segments. The tDCS was applied three times for each set in the learning segment (tDCS group, 14 participants) or not applied (sham group, 14 participants). The center of the anode was placed over the left M1, and the center of the reference electrode was placed over the right supraorbital area. The reaching error as task performance was analyzed by calculating the vertical distance from the line connecting the start and target at the cursor's maximum speed. We averaged the reaching error as a block of 10 trials and compared it between the tDCS and sham groups. Analyses of fMRI data were performed using SPM12. Brain activity was assessed by comparing the tDCS and sham groups in each segment.

The reaching error was significantly smaller in the late learning segment (block 13–18) and late recall segments (block 13), and significantly larger in the early washout segment (block 2–5) in the tDCS group than in the sham group. In a group comparison of brain activity, the caudate nucleus was activated during learning, washout and recall segments in the tDCS group than in the sham group after small-volume correction.

Using anodal tDCS on the M1 during force field adaptation facilitates and retains adaptation, with the involvement of the caudate nucleus being crucial for this outcome.

TDCS ¹

Skill Learning

Learning and Memory Other

Motor Behavior Other ²

Basal Ganglia

FUNCTIONAL MRI

Learning

Motor