Effects of Posterior Parietal Cortex and Cerebellum Anodal tDCS on Ankle Tracking Visuomotor Adaptation

Investigating How Cortical Modulation of the Cerebellum and Posterior Parietal Cortex Using Anodal tDCS Influences Ankle Motor Adaptation After Motor Learning

Motor adaptation is guided by state estimation, a dynamic prediction of the interaction consequences between body and environment in the sensorimotor system. Previous studies have shown that the posterior parietal cortex (PPC) and cerebellum are potential candidates for state estimators. However, neither direct evidence linking neural substrates of state estimation and motor adaptation nor the differences in state estimation in these two brain areas was presented. A comparison of neuromodulation effects over PPC and cerebellum in motor adaptation tasks could provide direct evidence to solve the knowledge gap.

Objective: This study aims to provide direct evidence to link state estimation and motor adaptation, and the neuromodulation effects of PPC and cerebellum in motor adaptation by using anodal transcranial direct current stimulation.

This was a single-blind, sham-controlled study. All participants were randomized to the PPC, cerebellum, and sham stimulation group. The ankle tracking system was used to record the ankle tracking visuomotor task during the motor learning phase, motor adaptation phase, and motor re-adaptation phase. Normalized root-mean squared error (RMSE) and RMSE reduction rate were measured as the performance outcome. A 20-minute atDCS at 2 mA anodal tDCS was given during the motor adaptation phase. The immediate effect and after effect of tDCS were seen in the motor adaptation phase and motor re-adaptation phase, respectively.

Inclusion Criteria:

• age between 20~29 years old
• normal ankle range of motion and muscle strength
• intact cognitive function (Mini-mental State Examination (MMSE) >27)
• corrected vision > 0.9.

Exclusion Criteria:

• any neurologic or psychiatric disease history
• musculoskeletal disease that interferes lower extremities movement
• severe cardiopulmonary or systematic disease (e.g. unstable angina, severe arrhythmia, heart failure, hypertrophic cardiomyopathy, aortic stenosis, pulmonary embolism, kidney failure)
• paresthesia
• seizure history
• brain surgery, meningitis, encephalitis history
• drainage tube on the head
• metal or other insertion in the brain
• insertion of electric medical device (e.g. pacemaker, cochlear implant)
• pregnancy
• taking central nervous system medication (e.g. antidepressants, anxiolytic)
• alcoholic addiction or drug abuse
• open wound, allergy, rash, or other illness that would affect the placement of tDCS
• headache, disgusting, vomit, or any other severe side effect to the tDCS