the effect of HD-tDCS on posture control
1=right HD-tDCS; 2=left HD-tDCS；3=bilateral HD-tDCS； 4=sham stimulation. The main purpose of this study is to explore whether HD-tDCS of the left-, right- or bilateral-parietal lobes would improve the ability of posture control and response, and whether they would improve the ability of visual, somatosensory and vestibular system to maintain posture control. The hypothesis of this study was that HD-tDCS of the unilateral and bilateral parietal lobes could improve the posture control and response. The right stimulation could promote the ability of visual system, and the left stimulation could promote the ability of somatosensory system to maintain stability. All participants completed the sensory organization test (SOT) and motor control test (MCT) on the Bertec® Balance Advantage®. SOT is a method to quantify the ability of the sensory system (visual, proprioception and vestibular system) to maintain balance by changing the reference conditions, which is composed of 6 conditions. The main outcome of SOT were equilibrium (ES), composite (CS) and sensory scores (visual VIS, somatosensory SOM ,vestibular VEST and visual preference PREF score). ES is generated for each condition and CS is a comprehensive score calculated based on the scores of each condition. A higher value representing greater balance performance. The CS is the most commonly used SOT score to assess postural control. The sensory score is a ratio calculated from the ES under different conditions. The SOM, VIS and VEST scores are used to assess the ability of each respective sensory system to maintain stability, and the PREF score assesses an individual’s reliance on visual information to control balance. MCT is designed to assess the latency and response strength of automatic response to horizontal platform translations in both forward and backward directions at three distinct magnitudes (mall, medium, and large). The main outcome of MCT were latency and response strength. The latency records the time from perturbation onset to mechanical response of each leg. The response strength is the instrument to quantify the force of the posture response. All data were averaged across the three successful trials completed by each participant.