Abstract WMP48: Estimated Electrical Field With Transcranial Direct Current Stimulation (tDCS) and Response to Gait Therapy Combined With tDCS in Chronic Stroke Patients

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Introduction: Transcranial Direct Current Stimulation (tDCS), a form of non-invasive brain stimulation, is a promising adjunct intervention that may enhance motor-learning induced neuroplasticity. It is safe and easy to administer, but current distribution can vary due to anatomy. Furthermore, it is not clear how strong the stimulation can and should be to achieve the best outcomes. In this analysis, we evaluated whether higher estimated electric field (e-field) is related to better response to gait training that is combined with tDCS. Methods: We used data of the active group from a randomized control trial testing response to 10-session gait therapy with or without tDCS. Therapy consisted of 30 min of virtual-reality obstacle clearance training on a treadmill followed by 30 min of overground stance phase training. Bihemispheric 2mA tDCS was delivered using 5x5 cm pads targeting primary motor areas during the first 15 min of training. Outcomes for this analysis included lower extremity Fugl-Meyer (FM) and Timed Up and Go (TUG). E-field was computed from a volume conduction model based on each individual’s structural MRI. The maximum electric field in sensorimotor cortical regions were extracted and correlated with post minus pre changes in outcome measures. Results: Active tDCS group’s (n=21) characteristics were 61.6±11.1 y/o; 28.6% female; 4.3±3.4 years post-stroke; 47.6% left affected hemisphere. Group improvements were: FM, 3 points (p= 0.0002); TUG, 2.74 s (p=0.0005). Correlation between the changes in FM and TUG was low (r=0.13). The highest e-field was 0.41±0.11 V/m, contralesionally and 0.39±0.11 V/m, ipsilesionally. The highest e-field occurred most commonly (in 13 out of 21 subjects) in the medial postcentral gyrus, both ipsi- and contralesionally. In the exploratory analysis of subjects who improved on both outcome measures (n=16), greater improvement on FM and TUG correlated with higher e-field strength for several regions (Table 1). Conclusion: Higher e-field produced by tDCS might influence response to rehabilitation. E-field that is achieved with tDCS is likely different in the ipsi- and contra-lesional hemispheres. These findings may need to be considered while designing tDCS intervention for post-stroke rehabilitation.

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