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Effects of pulse width, waveform and current direction in the cortex: A combined cTMS-EEG study

Casula, EP; Rocchi, L; Hannah, R; Rothwell, JC; (2018) Effects of pulse width, waveform and current direction in the cortex: A combined cTMS-EEG study. Brain Stimulation , 11 (5) pp. 1063-1070. 10.1016/j.brs.2018.04.015. Green open access

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Abstract

BACKGROUND: the influence of pulse width, pulse waveform and current direction on transcranial magnetic stimulation (TMS) outcomes is of critical importance. However, their effects have only been investigated indirectly with motor-evoked potentials (MEP). By combining TMS and EEG it is possible to examine how these factors affect evoked activity from the cortex and compare that with the effects on MEP. OBJECTIVE: we used a new controllable TMS device (cTMS) to vary systematically pulse width, pulse waveform and current direction and explore their effects on global and local TMS-evoked EEG response. METHODS: In 19 healthy volunteers we measured (1) resting motor threshold (RMT) as an estimate of corticospinal excitability; (2) global mean field power (GMFP) as an estimate of global cortical excitability; and (3) local mean field power (LMFP) as an estimate of local cortical excitability. RESULTS: RMT was lower with monophasic posterior-to-anterior (PA) pulses that have a longer pulse width (p < 0.001). After adjusting for the individual motor threshold of each pulse type we found that (a) GMFP was higher with monophasic pulses (p < 0.001); (b) LMFP was higher with longer pulse width (p = 0.015); (c) early TEP polarity was modulated depending on the current direction (p = 0.01). CONCLUSIONS: Despite normalizing stimulus intensity to RMT, we found that local and global responses to TMS vary depending on pulse parameters. Since EEG responses can vary independently of the MEP, titrating parameters of TMS in relation to MEP threshold is not a useful way of ensuring that a constant set of neurons is activated within a cortical area.

Type: Article
Title: Effects of pulse width, waveform and current direction in the cortex: A combined cTMS-EEG study
Location: United States
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.brs.2018.04.015
Publisher version: https://doi.org/10.1016/j.brs.2018.04.015
Language: English
Additional information: © 2018 Elsevier Inc. All rights reserved. This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: EEG, Motor cortex, Pulse waveform, Pulse width, TMS, cTMS
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > UCL Queen Square Institute of Neurology > Clinical and Movement Neurosciences
URI: http://discovery.ucl.ac.uk/id/eprint/10048132
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