P113. Effects of theta-burst rTMS on cortical networks as probed with TMS-evoked potentials

Publication date: August 2018

Source: Clinical Neurophysiology, Volume 129, Issue 8

Author(s): S.M. Günther, C. Tscherpel, L. Hensel, C. Grefkes

Background

Intermittent theta burst stimulation (iTBS) as a specific protocol of repetitive transcranial magnet stimulation (rTMS) has been shown to induce changes in cortical excitability that last beyond stimulation. However, effects are subject to a high degree of intra- and inter-individual variability (Hamada et al., 2013 Cereb Cortex; Diekhoff-Krebs et al., 2017 Neuroimage Clin.). Combining transcranial magnet stimulation (TMS) with electroencephalography (EEG) allows investigating cortical responses with high spatiotemporal specificity and sensitivity. Here, TMS-evoked potentials (TEPs) can be used to test the reactivity and connectivity of cortical areas and thereby to examine the direct effects of iTBS on the cortex. Therefore, the study aims at furthering our insights into the individual neural underpinnings underlying iTBS-induced changes of cortical excitability.

Methods

A group of young (20–35 years), healthy subjects received three serially applied blocks of iTBS over the primary motor cortex (M1 stimulation) or over parieto-occipital vertex as control condition (Sham stimulation) in two stimulation sessions (washout period: at least 10 days). As behavioural parameters, motor performance was assessed using two different motor tasks, Purdue Pegboard Test (PPT) and maximum finger tapping. TMS-EEG was recorded online at baseline and after each application of iTBS using a TMS-compatible 64-channel EEG-System (BrainProducts). Neuronavigated TMS was applied as single pulses with 80% of resting motor threshold (RMT).

Results (preliminary)

iTBS over M1 increased MEP amplitudes compared with sham stimulation after each stimulation block. There was, however, considerable between-subject differences in the individual responses to iTBS. In addition, iTBS increased performance in the Purdue Pegboard Test but not in the maximum finger tapping task. At the neural level, we found differential changes in TEP components, with enhancement of the N100 component which is thought to reflect inhibitory mechanisms.

Conclusion

This is the first study investigating network effects of iTBS by means of TMS-EEG. Our preliminary results suggest that iTBS causes effects at the behavioural and local level (cortical excitability) as well as affecting specific components of TMS-evoked potentials.

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