Abstract
Neural activity related to language can be modulated within widespread networks following learning or in response to disruption—including the experimental application of noninvasive brain stimulation. However, the spatiotemporal characteristics of such modulation remain insufficiently explored. The present study combined transcranial magnetic stimulation (TMS) and electroencephalography (EEG) to explore the modulation of activity across the language network following continuous theta-burst stimulation (cTBS) of the left pars opercularis. In 10 healthy subjects (21 ± 2 years old, four females), neuronavigated cTBS was delivered over the left pars opercularis of the frontal operculum (part of the traditional Broca’s area) at 80% of active motor threshold (AMT) stimulation intensity. Real cTBS and sham cTBS were performed in two different visits separated by at least 48 h. Before, immediately, and 10 min after cTBS, 30 single pulses of TMS were delivered to the left pars opercularis at 80% of the resting motor threshold (RMT), whereas EEG was simultaneously recorded. We examined the cTBS-induced modulation of phase locking values (PLVs) between the TMS-evoked potentials (TEPs) recorded over the pars opercularis and those recorded over its right-hemispheric homolog area, the left supramarginal area, and the left superior temporal area in different EEG frequency bands and different time windows following cTBS. cTBS to the left pars opercularis induced within the gamma band: (1) a significant increase in TEP phase synchronization between the left and right pars opercularis at an early time window (250–350 ms) following cTBS; and (2) significantly increased PLV with the left supramarginal area and the left superior temporal area at a later time window (600–700 ms). In the theta and delta band, cTBS to the left pars opercularis induced significantly increased phase synchronization of TEPs between the left pars opercularis and the posterior left hemispheric language areas at a late time window. In sham condition, there was a significant decrease in TEP phase synchronization of the high beta band between left pars opercularis and left superior temporal area at 200–300 ms. These results contribute to characterize the dynamics of the language network and may have implications in the development of noninvasive stimulation protocols to promote the language rehabilitation in aphasia patients.
Highlights
Language is processed in widely distributed neural networks including the frontal operculum (Broca’s region) in the dominant hemisphere and its right hemispheric homolog, as well as parietotemporal areas of the left hemisphere (Pulvermüller, 2002; Pulvermüller et al, 2009; Giraud and Poeppel, 2012; Poeppel et al, 2012)
In the gamma band (30–50 Hz) at a 250- to 350-ms time window, the phase synchronization of TEPs between the left and right pars opercularis significantly increased at T0 after real cTBS compared to baseline
At a later time window (600–700 ms), the phase synchronization of TEPs in the gamma band between the left pars opercularis and the left supramarginal region significantly increased at both T0 and T10 compared to baseline
Summary
Language is processed in widely distributed neural networks including the frontal operculum (Broca’s region) in the dominant hemisphere and its right hemispheric homolog, as well as parietotemporal areas of the left hemisphere (Pulvermüller, 2002; Pulvermüller et al, 2009; Giraud and Poeppel, 2012; Poeppel et al, 2012). Information flow across nodes of a network can be studied by recording synchronizations of spontaneous cortical oscillations. A study (Giraud et al, 2007) tried to link auditory structural characteristics of speech and spontaneous brain oscillations within networks important for speech perception and production. On the other hand, controlled perturbations applied directly to well-defined brain regions offer a superior strategy to gain insights into the casual interactions between nodes of a given large-scale brain network. We applied this strategy to gain insights into the dynamics across the language network
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