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Objective: We aimed at exploring the modulation of tDCS on spontaneous cortical activity through the changing of EEG rhythms to different tDCS montages and the interaction between cortical responses and variability factors of stroke individuals.Methods: 19 stroke subjects underwent 4 tDCS sessions with 3 different tDCS montages (anodal (atDCS), cathodal (ctDCS) and bilateral (bi-tDCS)) and sham stimulation in a single-blind, randomized, controlled crossover design. We acquired resting-state (eyes closing and opening alternately) EEG data before and after tDCS, and calculated the spectral power of each frequency band. Paired-samples T test was applied to examine the difference of spectral power between pre- and post-stimulation of each montage. Three-way repeated measures analysis of variance with lesion hemispheres, stimulation montages and locations were carried out to investigate tDCS effects of different lesion, montages, and channel locations, and the interaction. Further, the effects of tDCS over time were analyzed applying three-way repeated ANOVAs as well with post trials, lesion hemispheres and channel locations separately to each montage. Finally, linear and quadratic regression model were used separately to describe the association between clinical factors of stroke patients and change of spectral power.Results: We found that induced effect of tDCS was limited to the alpha rhythm of opening-state. atDCS increased the alpha power especially alpha1 (8-10 Hz) in local and distant areas of mainly frontal and partial. bi-tDCS affected the alpha power as well, but in a smaller area which mainly focused on alpha2 (10-13 Hz). ctDCS and sham had no effect on alpha rhythm. No significant difference of alpha band was found over the observed time range after the stimulation over. Results further showed that the quadratic model can better characterize the relationship between clinical factors and the tDCS effects of alpha rhythm than linear model. The changing of alpha especially alpha2 in contralateral hemisphere induced by atDCS was related to time since stroke, and alpha2 in ipsilateral hemisphere induced by bi-tDCS to motor impairment level.Conclusion: Our results provide electrophysiological evidence that different tDCS montages in stroke subjects modulate rhythmic cortical activity of alpha band in different ways, and the effects maintained for at least 30 minutes. The tDCS modulation effect was related to clinical factors, especially the time since stroke and the level of motor impairment. These findings are of great significance for the knowledge on modulation effect to stroke patients and for therapeutic application of motor recovery following stroke. |
