Abstract
Combining Transcranial Magnetic Stimulation (TMS) with electroencephalography (EEG) offers the opportunity to study signal propagation dynamics at high temporal resolution in the human brain. TMS pulse induces a local effect which propagates across cortical networks engaging distant cortical and subcortical sites. However, the degree of propagation supported by the structural compared to functional connectome remains unclear. Clarifying this issue would help tailor TMS interventions to maximize target engagement. The goal of this study was to establish the contribution of functional and structural connectivity in predicting TMSinducedsignal propagation after perturbation of two distinct brain networks. For this purpose,24 healthy individuals underwent two identical TMS-EEG visits where neuronavigated TMS pulses were delivered to nodes of the default mode network (DMN) and the dorsal attention network (DAN). The functional and structural connectivity derived from each individual stimulation spot were characterized via functional magnetic resonance imaging (fMRI) and Diffusion Weighted Imaging (DWI), and signal propagation across these two metrics was compared. Direct comparison between the signal extracted from brain regions either functionally or structurally connected to the stimulation sites, shows a stronger activation overcortical areas connected via white matter pathways, with a minor contribution of functional projections. This pattern was not observed when analyzing spontaneous resting state EEG activity. Overall, results suggest that structural links can predict network-level response to perturbation more accurately than functional connectivity. Additionally, DWI-based estimation of propagation patterns can be used to estimate off-target engagement of other networks and possibly guide target selection to maximize specificity.
Highlights
Combining Transcranial Magnetic Stimulation (TMS) with electroencephalography (EEG) offers the opportunity to study signal propagation dynamics at high temporal resolution in the human brain
The cluster threshold was determined as the 95th percentile of the cluster’s surrogate distribution and the area under the curve (AUC) of the significant clusters was extracted within the 350 ms post-TMS period, with positive and negative values indicating that the TMS-EEG signal propagated more on Diffusion Weighted Imaging (DWI) or functional magnetic resonance imaging (fMRI) projection map, respectively
To test whether the propagation/spread of TMS-induced potentials is better addressed by structural or functional connected cortical regions, the source reconstructed signals extracted from DWI and fMRI projection map were statistically compared across subjects
Summary
Combining Transcranial Magnetic Stimulation (TMS) with electroencephalography (EEG) offers the opportunity to study signal propagation dynamics at high temporal resolution in the human brain. The goal of this study was to establish the contribution of functional and structural connectivity in predicting TMSinducedsignal propagation after perturbation of two distinct brain networks For this purpose, healthy individuals underwent two identical TMS-EEG visits where neuronavigated TMS pulses were delivered to nodes of the default mode network (DMN) and the dorsal attention network (DAN). Direct comparison between the signal extracted from brain regions either functionally or structurally connected to the stimulation sites, shows a stronger activation overcortical areas connected via white matter pathways, with a minor contribution of functional projections This pattern was not observed when analyzing spontaneous resting state EEG activity. Considering the quest for data reproducibility, the same analyses were repeated on data collected on the same sample of healthy individuals across two separate study visits one month apart
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