The Effect of Sound and Stimulus Expectation on Transcranial Magnetic Stimulation-Elicited Motor Evoked Potentials

Antonio Capozio,Sarah Astill,Samit Chakrabarty

doi:10.1007/s10548-021-00867-9

Antonio Capozio, Sarah Astill + Show 1 more

Open Access

https://doi.org/10.1007/s10548-021-00867-9

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Journal: Brain Topography	Publication Date: Sep 6, 2021
Citations: 8	License type: open-access

Affiliation: University of Leeds

Abstract

The amplitude of motor-evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS) over the motor cortex is influenced by multiple factors. TMS delivery is accompanied by an abrupt clicking noise which can induce a startle response. This study investigated how masking/attenuating the sound produced by the TMS system discharging influences MEP amplitudes. In addition, the effects of increasing the time between consecutive stimuli and of making participants aware of the time at which they would be stimulated were studied. MEPs were recorded from the Flexor Carpi Radialis (FCR) muscle at rest by stimulation at motor threshold (MT), 120% MT and 140% MT intensity. Participants (N = 23) received stimulation under normal (NORMAL) conditions and while: wearing sound-attenuating earmuffs (EAR); listening to white noise (NOISE); the interval between stimuli were prolonged (LONG); stimulation timing was presented on a screen (READY). The results showed that masking (p = 0.020) and attenuating (p = 0.004) the incoming sound significantly reduced the amplitude of MEPs recorded across the intensities of stimulation. Increasing the interval between pulses had no effect on the recorded traces if a jitter was introduced (p = 1), but making participants aware of stimulation timing decreased MEP amplitudes (p = 0.049). These findings suggest that the sound produced by TMS at discharging increases MEP amplitudes and that MEP amplitudes are influenced by stimulus expectation. These confounding factors need to be considered when using TMS to assess corticospinal excitability.

Highlights

transcranial magnetic stimulation (TMS) is a non-invasive technique that can be used to study changes in the excitability of the motor system in both experimental (Pascual-Leone et al 1994) and clinical settings (Hamzei et al 2006)
Three participants could not tolerate the 140% motor threshold (MT) stimulation intensity and for these three subjects motor-evoked potentials (MEPs) amplitudes elicited at this intensity were not collected (N = 20)
The main aims of the presented study were to: (1) determine the outcome of attenuating and masking the sound produced by TMS discharging on the MEPs recorded upon M1 stimulation; (2) investigate the effects of stimulus expectation on the MEPs recorded upon M1 stimulation

Summary

Introduction

TMS is a non-invasive technique that can be used to study changes in the excitability of the motor system in both experimental (Pascual-Leone et al 1994) and clinical settings (Hamzei et al 2006). A single TMS pulse, when applied to the primary motor cortex (M1), can elicit an MEP in the muscles induced by descending activity along the corticospinal tract, as measured via electromyography (EMG) (Hallett 2007). Multiple sensory and psychological factors can influence the effects of TMS delivered to the motor cortex (Duecker and Sack 2015), limiting the validity of the results in terms of corticospinal excitability. The auditory activation correlates with the amplitude of the delivered TMS pulse (Goetz et al 2015). Auditory stimuli might activate the reticulospinal tract and modulate the excitability of spinal motoneurons (Dean and Baker 2017), which determines the outcome of TMS on the motor cortex (Burke and Pierrot-Deseilligny 2010).

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