Transcranial direct current stimulation (tDCS) has become a new method of rehabilitation treatment for stroke and is gradually gaining acceptance. However, the neurophysiological mechanisms of tDCS in the treatment of stroke still need to be further explored. In our research, we aimed to investigate the effects of tDCS on neural oscillation power and brain functional network (BFN) connectivity in stroke patients based on electroencephalogram (EEG). Fifteen patients with ischemic stroke attended two experimental sessions in a randomized crossover trial and received real and sham tDCS. Resting-state EEG signals were acquired before and after stimulation. First, the power of EEG delta, theta, alpha, beta, and gamma bands were analyzed before and after stimulation. Then, BFNs in different bands were constructed, and network characteristic parameters such as degree, clustering coefficient, characteristic path length, global efficiency, and small-world attribute were analyzed. The results showed that the delta power decreased significantly ( P <0.05) and the alpha power increased significantly ( P <0.05) after real tDCS, whereas the theta, beta, and gamma power did not change significantly ( P >0.05). The degree and global efficiency of the delta band BFN decreased significantly after real tDCS ( P <0.05), the characteristic path length increased significantly ( P <0.05), and the clustering coefficient and small-world attribute decreased but not statistically significant ( P >0.05). The degree, clustering coefficient, global efficiency, and small-world attribute of the alpha band BFN increased significantly after real tDCS ( P <0.05), and the characteristic path length decreased significantly ( P <0.05). The BFN characteristic parameters in theta, beta, and gamma bands did not change significantly after real tDCS ( P >0.05). There was no significant difference in sham tDCS group ( P >0.05). Our study found that the power of delta oscillations decreased and the global connectivity of delta band BFN weakened after tDCS in stroke patients, whereas the power of alpha oscillations increased and the global and local connectivity of alpha band BFN was enhanced. The findings implied that one of the neurophysiological mechanisms of tDCS treatment in stroke patients may be the modulation of the power of delta and alpha oscillations, as well as the improvement of the connectivity of delta and alpha oscillation networks.

Transcranial direct current stimulation (tDCS) provides a way to modulate the cortical activity and promote motor rehabilitation following stroke. However, evidence indicates that the response to tDCS is highly variable. This study was aimed at exploring rhythmic response of Electroencephalography (EEG) to three tDCS protocols in stroke subjects. We hypothesize that tDCS protocols may interact with stoke characteristics, and electrode placement may affect cortical activity which could be reflected by the EEG rhythm. 32 subjects with unilateral stroke were recruited to a single-blinded, randomized, and controlled crossover experiment. All of the subjects underwent four tDCS protocols (anodal (atDCS), cathodal (ctDCS), and bilateral tDCS (bi-tDCS) and sham) with an interval of at least 1 week. Resting-state EEG was acquired before and after the stimulation. We tested the change of EEG spectral power after tDCS and the difference of change among four protocols using the paired-sample -test and repeated measures analysis of variance. Then, we investigated the clinical factors affecting the above changes using the linear and quadratic regression model. According to the results, EEG responded to atDCS and bi-tDCS protocols on alpha and beta rhythm and subjects with a left lesion had higher response than those with the right lesion. Besides that, the change of alpha and beta power after atDCS and of beta power after bi-tDCS showed association with clinical characteristics only in subjects with the left lesion. In conclusion, the study found varied EEG response with different protocols, lesion hemispheres, and other clinical characteristics supporting the individualized cortical oscillatory effect induced by tDCS.

Transcranial direct current stimulation (tDCS) is an emerging brain intervention technique. However, the effects of tDCS on stroke patients are unclear. In this study, Granger Causality (GC) is used to construct brain functional networks of the tDCS group (9 cases) and the sham tDCS group (11 cases). Some parameters of brain functional networks are analyzed comparatively, such as degree, clustering coefficient, betweenness centrality, characteristic path length, and efficiency. In tDCS group, the results show that the distribution of degree changes greatly in left prefrontal lobe and left temporal lobe regions, the distribution of betweenness centrality transfers, characteristic path length decreases, clustering coefficient and efficiency increase significantly ( $p< 0.05$ ) after stimulation. However, there is no significant difference in sham tDCS group. In this study, the positive effects of tDCS on the therapeutic of stroke are clarified and the evidence for the effects of tDCS on stroke is provided.

Autism spectrum disorder (ASD) is a devastating mental disorder in children. Currently, there is no effective treatment for ASD. Transcranial direct current stimulation (tDCS), which is a non-invasive brain stimulation neuromodulation technology, is a promising method for the treatment of ASD. However, the manner in which tDCS changes the electrophysiological process in the brain is still unclear. In this study, we used tDCS to stimulate the dorsolateral prefrontal cortex area of children with ASD (one group received anode tDCS, and the other received sham tDCS) and investigated the changes in evoked EEG signals and behavioral abilities before and after anode and sham stimulations. In addition to tDCS, all patients received conventional rehabilitation treatment. Results show that although conventional treatment can effectively improve the behavioral ability of children with ASD, the use of anode tDCS with conventional rehabilitation can boost this improvement, thus leading to increased treatment efficacy. By analyzing the electroencephalography pre- and post-treatment, we noticed a decrease in the mismatch negativity (MMN) latency and an increase in the MMN amplitude in both groups, these features are considered similar to MMN features from healthy children. However, no statistical difference between the two groups was observed after 4 weeks of treatment. In addition, the MMN features correlate well with the aberrant behavior checklist (ABC) scale, particularly the amplitude of MMN, thus suggesting the feasibility of using MMN features to assess the behavioral ability of children with ASD.

Objective: Repetitive transcranial magnetic stimulation (rTMS) is an effective technique promoting motor function recovery after stroke. Our study aimed to reveal the functional neural reorganization of rTMS with motor training in stroke from a comprehensive multimodal perspective. Methods: This study proposed a novel EEG-fNIRS multilayer brain network analysis method to investigate the hemisphere activation and neuroplasticity changes and conducted clinical study. Specifically, the EEG-fNIRS signals were first reconstructed and aligned in the unified cortical source space. Then, the neurovascular coupling strength was quantified by subject-specific estimation and utilized to build the inter-layer edges. Subsequently, the intra-layer and inter-layer edges were combined to construct the multilayer brain network, of which features were extracted. 27 stroke patients and 13 healthy controls were recruited in the clinical experiment. Results: We found that the rTMS group showed significant improvement in the neurovascular coupling levels and multiplex clustering coefficients compared with the sham group. Moreover, these neural changes were significantly correlated with the motor function improvements (${\mathit{R}}$ = 0.600 and 0.618). The proposed method reduces the prediction error for rehabilitation outcomes by 20.36% on average over unimodal approaches. Conclusion: The results indicated that our method effectively reveals the functional neural reorganization of rTMS with motor training in stroke. Significance: This work provides a novel method to empower neuroelectric-hemodynamic analysis and offers unique insights into stroke recovery mechanisms induced by rTMS combined with motor training.