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

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.

Transcranial Direct Current Stimulation Combined With Listening to Preferred Music Alters Cortical Speech Processing in Older Adults

“…Thus, the orientation and location of intracranial current densities induced by tDCS were not optimized for neuromodulation of lower auditory brain areas (i.e., brainstem). However, we note that even with more optimal foci for auditory neuromodulation (e.g., superior temporal lobe), the effects of magnetic (TMS) and current (tDCS) stimulation on FFRs remains equivocal ( López-Caballero et al, 2020 ; Mai and Howell, 2021 ). For example, continuous theta burst TMS over right auditory cortex fails to yield measurable changes in FFRs suggesting deeper, more peripheral sources (i.e., brainstem) which are insensitive to cortical stimulation ( López-Caballero et al, 2020 ).…”

“…However, we note that even with more optimal foci for auditory neuromodulation (e.g., superior temporal lobe), the effects of magnetic (TMS) and current (tDCS) stimulation on FFRs remains equivocal ( López-Caballero et al, 2020 ; Mai and Howell, 2021 ). For example, continuous theta burst TMS over right auditory cortex fails to yield measurable changes in FFRs suggesting deeper, more peripheral sources (i.e., brainstem) which are insensitive to cortical stimulation ( López-Caballero et al, 2020 ). In contrast, Mai and Howell (2021) showed that tDCS neurostimulation over right auditory cortex can cause subtle decreases in speech-FFR amplitudes (i.e., F0 coding), though apparently without concomitant changes in pitch discrimination behavior ( Mai and Howell, 2021 ).…”

“… Heimrath et al (2016) found anodal tDCS over temporal lobe increased the P1 (∼50 ms) response to consonant-vowel speech tokens similar to those used here. However, other studies have failed to observe significant ERP changes with similar tDCS stimulation protocols ( Kunzelmann et al, 2018 ; López-Caballero et al, 2020 ). Our study differs from prior work in that our stimulation targets were located over frontal (rather than auditory temporal) cortical sites.…”

Continuous theta burst TMS of area MT+ impairs attentive motion tracking

“…Our current results warrant further research that directly compares the lateralization of right versus left MT+ stimulation effects on MOT. Second, although we used fMRI guided neuronavigation to target cTBS, we cannot rule out the possibility that cTBS effects propagated to surrounding cortical areas and/or altered activity (Casula et al, 2016;L opez-Caballero et al, 2020;Rocchi et al, 2018) in other nodes of the neural network involved in MOT. Third, because we did not include a low-level motion control task, we do not know the extent to which motion processing deficits per se were involved in reduced MOT task performance following active MT+ cTBS.…”

Duplex perception reveals brainstem auditory representations are modulated by listeners’ ongoing percept for speech

“…FFRs are scalp-recorded potentials reflecting a mixture of phase locked activity from several nuclei along the auditory pathway (Smith et al 1975;Sohmer et al 1977;Skoe and Kraus 2010;. Though cortex can contribute to FFRs under limited circumstances (Coffey, Herholz, et al 2016), speech-FFRs are dominantly generated by midbrain sources (i.e., inferior colliculus, IC) when recorded via EEG using high (> 150 Hz) fundamental frequency stimuli (Kiren et al 1994;López-Caballero et al 2020;Bidelman and Momtaz 2021;Gorina-Careta et al 2021;Price and Bidelman 2021). While the IC is likely too early along the processing hierarchy to show bottom-up, categorical organization de novo, top-down influences from cortex via the descending corticofugal system (Gao and Suga 1998) could modulate brainstem speech representations to produce categorical encoding effects as was recently observed in human FFRs (Price and Bidelman 2021;Lai et al 2022;Carter and Bidelman 2023;Lai et al 2023).…”