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Brainstem correlates of cochlear nonlinearity measured via the scalp-recorded frequency-following response.

ABSTRACT: The frequency-following response (FFR) is an EEG-based potential used to characterize the brainstem encoding of complex sounds. Adopting techniques from auditory signal processing, we assessed the degree to which FFRs encode important properties of cochlear processing (e.g. nonlinearities) and their relation to speech-in-noise (SIN) listening skills. Based on the premise that normal cochlear transduction is characterized by rectification and compression, we reasoned these nonlinearities would create measurable harmonic distortion in FFRs in response to even pure tone input. We recorded FFRs to nonspeech (pure- and amplitude-modulated-tones) stimuli in normal-hearing individuals. We then compared conventional indices of cochlear nonlinearity, via distortion product otoacoustic emission (DPOAE) I/O functions, to total harmonic distortion measured from neural FFRs (FFRTHD). Analysis of DPOAE growth and the FFRTHD revealed listeners with higher cochlear compression thresholds had lower neural FFRTHD distortion (i.e. more linear FFRs), thus linking cochlear and brainstem correlates of auditory nonlinearity. Importantly, FFRTHD was also negatively correlated with SIN perception whereby listeners with higher FFRTHD (i.e. more nonlinear responses) showed better performance on the QuickSIN. We infer individual differences in SIN perception and FFR nonlinearity even in normal-hearing individuals may reflect subtle differences in auditory health and suprathreshold hearing skills not captured by normal audiometric evaluation. Future studies in hearing-impaired individuals and animal models are necessary to confirm the diagnostic utility of FFRTHD and its relation to cochlear hearing loss or peripheral neurodegeneration in humans.

SUBMITTER: Bidelman GM

PROVIDER: S-EPMC7275900 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:AimRipple-band epileptic high-frequency oscillations (HFOs) can be recorded by scalp electroencephalography (EEG), and tend to be associated with epileptic spikes. However, there is a concern that the filtration of steep waveforms such as spikes may cause spurious oscillations or "false ripples." We excluded such possibility from at least some ripples by EEG differentiation, which, in theory, enhances high-frequency signals and does not generate spurious oscillations or ringing.MethodsThe subjects were 50 pediatric patients, and ten consecutive spikes during sleep were selected for each patient. Five hundred spike data segments were initially reviewed by two experienced electroencephalographers using consensus to identify the presence or absence of ripples in the ordinary filtered EEG and an associated spectral blob in time-frequency analysis (Session A). These EEG data were subjected to numerical differentiation (the second derivative was denoted as EEG″). The EEG″ trace of each spike data segment was shown to two other electroencephalographers who judged independently whether there were clear ripple oscillations or uncertain ripple oscillations or an absence of oscillations (Session B).ResultsIn Session A, ripples were identified in 57 spike data segments (Group A-R), but not in the other 443 data segments (Group A-N). In Session B, both reviewers identified clear ripples (strict criterion) in 11 spike data segments, all of which were in Group A-R (p < 0.0001 by Fisher's exact test). When the extended criterion that included clear and/or uncertain ripples was used in Session B, both reviewers identified 25 spike data segments that fulfilled the criterion: 24 of these were in Group A-R (p < 0.0001).DiscussionWe have demonstrated that real ripples over scalp spikes exist in a certain proportion of patients. Ripples that were visualized consistently using both ordinary filters and the EEG″ method should be true, but failure to clarify ripples using the EEG″ method does not mean that true ripples are absent.ConclusionThe numerical differentiation of EEG data provides convincing evidence that HFOs were detected in terms of the presence of such unusually fast oscillations over the scalp and the importance of this electrophysiological phenomenon.

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Brainstem correlates of cochlear nonlinearity measured via the scalp-recorded frequency-following response.

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