1. Purpose
In this study, we investigated differences of the resting-state functional connectivity after dual site transcranial direct stimulation (tDCS) for modulation of gait-related neural network plasticity using functional near-infrared spectroscopy (fNIRS) in stroke patients.

2. Methods
Twenty stroke patients participated in this single-blind, randomized cross-over study. Four conditions were randomly applied with 24 hours of washout period between each condition: dual-site anodal stimulation over the bihemispheric primary leg motor area (M1leg) and supplementary motor area (SMA); anodal stimulation over the ipsilesional M1leg and SMA; anodal stimulation over the contralesional M1leg and SMA; sham stimulation. Two battery-driven stimulators were used with 2 mA direct current in each anode. Cathodal electrodes were placed on bilateral supraorbital areas. During the 30 minutes of stimulation, subjects took rest in the early and late 10 minutes and walking on a treadmill in the middle 10 minutes. The hemodynamic responses were recorded by an fNIRS system at before and after the intervention. Pearson correlation coefficient was generated from oxyhemoglobin signals.

3. Results
To confirm the changes of the connectivity after tDCS stimulation compared with the sham stimulation, the network change was investigated by thresholding based on the correlation coefficient value of 0.6. The network changes after dual-site stimulation was noticeable compared to single or sham stimulation conditions. Connectivity between sensorimotor-related areas such as M1leg, SMA, and primary sensory motor cortex was increased after dual-site stimulation.   

4. Conclusions
This study implies dual-site tDCS may enhance the neuromodulation effect in the gait-related motor network compared to the conventional single-site stimulation in stroke patients.

Acknowledgement
This research was supported by a grant from the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of Korea (HI17C1501) and NRF (NRF-2017R1A2A1A05000730, NRF-2017M3A9G5083690) funded by the Korean government.

CHANGES OF RESTING-STATE FUNCTIONAL CONNECTIVITY AFTER DUAL-SITE TRANCSCRAINAL DIRECT CURRENT STIMULATION FOR ENHANCING NEURAL PLASTICITY OF GAIT-RELATED MOTOR NETWORK IN STROKE PATIENTS: AN FNIRS STUDY