Specificity of the Human Frequency Following Response for Carrier and Modulation Frequency Assessed Using Adaptation.

Hedwig E Gockel,Christopher J Plack,Robert P Carlyon,Alexandra Krugliak

doi:10.1007/s10162-015-0533-9

Abstract

The frequency following response (FFR) is a scalp-recorded measure of phase-locked brainstem activity to stimulus-related periodicities. Three experiments investigated the specificity of the FFR for carrier and modulation frequency using adaptation. FFR waveforms evoked by alternating-polarity stimuli were averaged for each polarity and added, to enhance envelope, or subtracted, to enhance temporal fine structure information. The first experiment investigated peristimulus adaptation of the FFR for pure and complex tones as a function of stimulus frequency and fundamental frequency (F0). It showed more adaptation of the FFR in response to sounds with higher frequencies or F0s than to sounds with lower frequency or F0s. The second experiment investigated tuning to modulation rate in the FFR. The FFR to a complex tone with a modulation rate of 213 Hz was not reduced more by an adaptor that had the same modulation rate than by an adaptor with a different modulation rate (90 or 504 Hz), thus providing no evidence that the FFR originates mainly from neurons that respond selectively to the modulation rate of the stimulus. The third experiment investigated tuning to audio frequency in the FFR using pure tones. An adaptor that had the same frequency as the target (213 or 504 Hz) did not generally reduce the FFR to the target more than an adaptor that differed in frequency (by 1.24 octaves). Thus, there was no evidence that the FFR originated mainly from neurons tuned to the frequency of the target. Instead, the results are consistent with the suggestion that the FFR for low-frequency pure tones at medium to high levels mainly originates from neurons tuned to higher frequencies. Implications for the use and interpretation of the FFR are discussed.

Highlights

An important obstacle to understanding the neural basis of human hearing is that, while a wide range of physiological techniques can be used with animals, many of those techniques are invasive and unsuitable for human participants
It has been argued that the frequency following response (FFR) to low-frequency pure tones at medium-to-high-levels is generated not from neurons tuned to the tone frequency, but from neurons having a wide range of characteristic frequencies (CFs) above the tone frequency (Dau 2003)
It has been shown that the time course of spike rate adaptation of auditory nerve fibers (ANFs) during pure tone bursts is related to neural characteristic frequency (CF); ANFs with higher CFs tend to adapt more quickly than ANFs with lower CFs (Westerman and Smith 1984, 1985; Crumling and Saunders 2007)

Summary

Introduction

An important obstacle to understanding the neural basis of human hearing is that, while a wide range of physiological techniques can be used with animals, many of those techniques are invasive and unsuitable for human participants. GOCKEL ET AL.: Frequency following response ration employed here, is thought to reflect phaselocked activity at the level of the inferior colliculus (IC) and/or lateral lemniscus (LL). It has been proposed as a method for studying basic aspects of auditory function and for assessing a range of disorders including reading problems in children (Hornickel et al 2012) and Bhidden hearing loss,^ i.e., auditory neuropathy that is not thought to be detectable by measuring standard audiometric thresholds (Bharadwaj et al 2014). That evidence came from the finding that the spectrum of the FFR to a dichotic harmonic complex, in which different components are presented to opposite ears, does not correspond to the perceived pitch but, instead, resembles the sum of the responses to each ear’s input presented separately

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Conclusion