Effects of cTBS on the Frequency-Following Response and Other Auditory Evoked Potentials.

Pablo Martin-Trias,Natàlia Gorina-Careta,Teresa Ribas-Prats,Carles Escera,Fran López-Caballero,David Bartrés-Faz

doi:10.3389/fnhum.2020.00250

Abstract

The frequency-following response (FFR) is an auditory evoked potential (AEP) that follows the periodic characteristics of a sound. Despite being a widely studied biosignal in auditory neuroscience, the neural underpinnings of the FFR are still unclear. Traditionally, FFR was associated with subcortical activity, but recent evidence suggested cortical contributions which may be dependent on the stimulus frequency. We combined electroencephalography (EEG) with an inhibitory transcranial magnetic stimulation protocol, the continuous theta burst stimulation (cTBS), to disentangle the cortical contribution to the FFR elicited to stimuli of high and low frequency. We recorded FFR to the syllable /ba/ at two fundamental frequencies (Low: 113 Hz; High: 317 Hz) in healthy participants. FFR, cortical potentials, and auditory brainstem response (ABR) were recorded before and after real and sham cTBS in the right primary auditory cortex. Results showed that cTBS did not produce a significant change in the FFR recorded, in any of the frequencies. No effect was observed in the ABR and cortical potentials, despite the latter known contributions from the auditory cortex. Possible reasons behind the negative results include compensatory mechanisms from the non-targeted areas, intraindividual variability of the cTBS effectiveness, and the particular location of our target area, the primary auditory cortex.

Highlights

The frequency-following response (FFR) is a sustained evoked potential recorded with electroencephalography (EEG) or magnetoencephalography (MEG) that mimics the periodic features of the auditory stimulus waveform
Statistical comparisons of the time domain signalto-noise ratio (SNR) revealed a main effect of the frequency factor in all three portions of the FFR [Transient, F(1,19) = 69.53, p < 0.001, η2p = 0.785; Constant, F(1,19) = 60.27, p < 0.001, η2p = 0.760; Total, F(1,19) = 72.23, p < 0.001, η2p = 0.792], indicating that the magnitude of the neural activity relative to the baseline was larger for FFR elicited to low-frequency stimuli
In spite of the robust and compelling auditory evoked potential (AEP) obtained at all levels recorded (FFR, auditory brainstem response (ABR), and cortical potentials), our results suggest no effect of continuous theta burst stimulation (cTBS) on the auditory cortex, as cortical potentials were not affected, leaving results on the FFR uninterpretable

Summary

Introduction

The frequency-following response (FFR) is a sustained evoked potential recorded with electroencephalography (EEG) or magnetoencephalography (MEG) that mimics the periodic features of the auditory stimulus waveform. It appears after the transient V—a complex of the phasic auditory brainstem response (ABR), for which it is sometimes described as the sustained part of the ABR (Skoe and Kraus, 2010). FFR has been shown to be sensitive to different phenomena related to auditory perception and, in turn, to higher-level processing of language and music. On the genetic aspects of the FFR, the involvement of the serotonin transporter expression has been revealed (Selinger et al, 2016)

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