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Continuous theta-burst stimulation (cTBS) induces long-lasting inhibitory effects on cortical excitability. Although cTBS has been reported to modulate neural oscillations and functional connectivity, it is still unclear how cTBS affects brain dynamics that could be captured by the resting-sate EEG microstate sequences. This study aims to investigate how cTBS over the left motor cortex affects brain dynamics. We applied 40 s-long cTBS over the left motor cortex of 28 healthy participants. Before and in multi-sessions up to 90 min after cTBS, their performance in a Nine-Hole Peg Test (NHPT), that measures the hand dexterity, and resting state EEG were recorded. Resting-sate EEG data were clustered into four microstates (namely A, B, C, and D) using k-means clustering algorithms. cTBS-induced changes in NHPT performance, microstate dynamics and functional connectivity networks were comprehensively assessed. As compared with baseline, the completion time of NHPT became shorter immediately after cTBS, suggesting cTBS-induced motor function improvement. After cTBS, the topography of microstate B revealed a greater change compared with other three topographies. Importantly, cTBS-induced decrease in completion time of NHPT correlated with cTBS-induced decrease of the mean occurrence of microstate B. Functional connectivity analysis further revealed that cTBS led to an increase of the node efficiency at C4 electrode in microstate B. These results indicated the specific modulation of cTBS over the motor cortex on the dynamics of microstate B. This work provided the evidence of the association between B and motor function, and it also implies the modulation of cTBS over the motor network. [ABSTRACT FROM AUTHOR]

This study aims to reveal dynamic brain networks during speech perception. All male subjects were presented five English vowel [a], [e], [i], [o], and [u] stimuli. Brain dynamics were decoded using multivariate Gaussian hidden Markov model (MGHMM), which trained on spatiotemporal patterns of broadband multivariate event-related potential amplitudes to identify distinct broadband EEG microstates (MS), microstate source imaging, and microstate functional connectivity (μFC). Obtained results showed fluctuated cortical generators and μFC in eight microstates throughout the perception. Microstate source imaging revealed involvements of bilateral (left-side dominance) posterior superior temporal cortex (TC), inferior frontal gyrus (IFG), and supramarginal regions in perception. Precentral cortex where primary motor cortex located was also significantly activated. These regions were early appeared at 96-151 ms (left-side dominance) and at 186-246 ms (left hemisphere only) after the stimuli onset. Results from μFC revealed significant increases in delta (2.5-4.5 Hz), theta (4.5-8.5 Hz), alpha (12.5-14.5 Hz), beta (22.5-24.5 Hz), low gamma (30.5-32.5, 38.5-40.5 Hz) but decreases in high gamma (42.5-46.5 Hz) bands in perception. Increased FC were observed mainly at; (1) microstate segments 34-95 ms (MS2) and 96-151 ms (MS3) in early stages, (2) microstate intervals 186-246 ms (MS5) and 297-449 ms (MS6) in subsequent stages of perception. We found that stronger statistical FC differences in perception at TCs, with respect to left IFG (Broca' area), left TC, and precentral areas. Furthermore, by conducting a comparative protocol measuring FC distinction degree, we showed performance improvements of 8.01% (p-value = 0.0162), 14.41% (pvalue = 0.006) when compared MGHMM to well established Lehmann-based modified K-means, Atomize and Agglomerative Hierarchical Clustering and 8.791% (p-value = 0.0097) over the combination of K-means and sliding window methods, respectively. This study indicates the usefulness of EEG microstates to investigate broadband brain dynamics in speech perception. The current findings based on male subjects would be generalized more by future studies with a larger appropriate sample size including female subjects.