Neural effects of TMS trains on the human prefrontal cortex

Abstract

Despite adoption of repetitive TMS (rTMS) for the treatment of neuropsychiatric disorders, a lack of understanding of its neural effects limits our ability to monitor, personalize, and adapt treatments. Here we address the methodological limitations in capturing the neural response to a single TMS train, the fundamental building block of treatment. We developed methods to measure these effects noninvasively and evaluated the acute neural response to single and sequential TMS trains. In 16 healthy adults, we applied 10 Hz trains to the dorsolateral prefrontal cortex (dlPFC) in a randomized, sham-controlled, event-related design and assessed changes to the TMS-evoked potential (TEP), a measure of local cortical excitability. We hypothesized that single TMS trains would induce changes in the local TEP amplitude that would accumulate across trains, but we found no evidence in support of this hypothesis. However, exploratory analyses demonstrated modulations non-locally and in phase and source space. Single and sequential TMS trains may not be sufficient to modulate the local TEP amplitude, but induce acute neural changes measured in alternative ways. This work should be contextualized as methods development for the monitoring of transient neural changes during rTMS and contributes to a growing understanding of the neural effects of rTMS.

Theta-burst direct electrical stimulation remodels human brain networks

“…The two most predictive features we observed were 1) the distance to the stimulation site and 2) CCEP amplitude. Translating this to the non-invasive space, diffusion-tensor imaging (DTI) could be employed to define anatomical tracts, while single pulse stimulation using TMS and recording with EEG can be used to index effective connectivity [110][111][112][113][114][115] . Based on these two parameters, a gradient of how likely the target brain area would undergo plasticity from stimulation at different locations can be constructed, prior to any stimulation.…”

TMS provokes target-dependent intracranial rhythms across human cortical and subcortical sites

“…Although neural oscillations are critical in neuropsychiatric disease, we have only a limited understanding of how TMS affects such oscillatory neural activity (19,20). Studies combining scalp EEG recordings and TMS tend to focus on the evoked responses (termed TMSevoked potentials, or TEPs (10,(22)(23)(24)(25)(26)(27)), which are phase-locked to stimulation and are typically thought of as a signature of bottom-up propagation of activity. Some investigators have attempted to differentiate these evoked responses from "true" oscillations that occur with variable phase relation to the stimulus (28)(29)(30)(31) (also called "induced"), as these may reflect higher-order cognitive processing.…”