The spectral features of EEG responses to transcranial magnetic stimulation of the primary motor cortex depend on the amplitude of the motor evoked potentials.

Matteo Fecchio,Silvia Casarotto,Simone Russo,Chiara-Camilla Derchi,Fabio Ferrarelli,Alice Mazza,Simone Sarasso,Maurizio Mariotti,Ulf Ziemann,Andrea Pigorini,Mario Rosanova,Federico Resta,Angela Comanducci,Marcello Massimini,Isabella Premoli

doi:10.1371/journal.pone.0184910

Abstract

Transcranial magnetic stimulation (TMS) of the primary motor cortex (M1) can excite both cortico-cortical and cortico-spinal axons resulting in TMS-evoked potentials (TEPs) and motor-evoked potentials (MEPs), respectively. Despite this remarkable difference with other cortical areas, the influence of motor output and its amplitude on TEPs is largely unknown. Here we studied TEPs resulting from M1 stimulation and assessed whether their waveform and spectral features depend on the MEP amplitude. To this aim, we performed two separate experiments. In experiment 1, single-pulse TMS was applied at the same supra-threshold intensity on primary motor, prefrontal, premotor and parietal cortices and the corresponding TEPs were compared by means of local mean field power and time-frequency spectral analysis. In experiment 2 we stimulated M1 at resting motor threshold in order to elicit MEPs characterized by a wide range of amplitudes. TEPs computed from high-MEP and low-MEP trials were then compared using the same methods applied in experiment 1. In line with previous studies, TMS of M1 produced larger TEPs compared to other cortical stimulations. Notably, we found that only TEPs produced by M1 stimulation were accompanied by a late event-related desynchronization (ERD—peaking at ~300 ms after TMS), whose magnitude was strongly dependent on the amplitude of MEPs. Overall, these results suggest that M1 produces peculiar responses to TMS possibly reflecting specific anatomo-functional properties, such as the re-entry of proprioceptive feedback associated with target muscle activation.

Highlights

The combination of Transcranial Magnetic Stimulation with electroencephalogram (TMS/ EEG) allows recording the immediate response of the cerebral cortex to a focal perturbation with good spatial and temporal resolution [1]
With respect to the EEG responses in the time-frequency domain (ERSP) we observed that all targeted cortical areas responded to Transcranial magnetic stimulation (TMS) with a broadband increase of spectral power lasting up to ~200 ms (Fig 1E)
Regarding the effects of motor evoked potentials (MEPs) amplitude on the spectral features of the local M1 EEG response, we found that the amount of event related desynchronization (ERD) was significantly reduced (83.9 ± 22.9; Fig 2D, right panel) in the low-MEP condition as compared to the high-MEP condition (Wilcoxon signed rank test, p

Summary

Introduction

The combination of Transcranial Magnetic Stimulation with electroencephalogram (TMS/ EEG) allows recording the immediate response of the cerebral cortex to a focal perturbation with good spatial and temporal resolution [1]. Several TMS/EEG studies have been conducted both on primary motor and sensory cortical areas [5,9,10,11,12,13,14,15,16,17] as well as associative cortical areas [6,7,18,19,20,21,22] In this respect, the primary motor cortex (M1) has been largely used as the elective experimental model to study brain reactivity to TMS. Other studies focused on possible relationship between specific TEPs components, in the time domain, possibly modulated by the presence of MEP. Nobody investigated, in the time-frequency domain, if and how the amplitude of MEPs influences TEPs

Methods

Results

Conclusion