Elsevier

Hearing Research

Volume 298, April 2013, Pages 73-79
Hearing Research

Research paper
Rapid measurement of auditory filter shape in mice using the auditory brainstem response and notched noise

https://doi.org/10.1016/j.heares.2013.01.002Get rights and content

Abstract

The notched noise method is an effective procedure for measuring frequency resolution and auditory filter shapes in both human and animal models of hearing. Briefly, auditory filter shape and bandwidth estimates are derived from masked thresholds for tones presented in noise containing widening spectral notches. As the spectral notch widens, increasingly less of the noise falls within the auditory filter and the tone becomes more detectible until the notch width exceeds the filter bandwidth. Behavioral procedures have been used for the derivation of notched noise auditory filter shapes in mice; however, the time and effort needed to train and test animals on these tasks renders a constraint on the widespread application of this testing method. As an alternative procedure, we combined relatively non-invasive auditory brainstem response (ABR) measurements and the notched noise method to estimate auditory filters in normal-hearing mice at center frequencies of 8, 11.2, and 16 kHz. A complete set of simultaneous masked thresholds for a particular tone frequency were obtained in about an hour. ABR-derived filter bandwidths broadened with increasing frequency, consistent with previous studies. The ABR notched noise procedure provides a fast alternative to estimating frequency selectivity in mice that is well-suited to high through-put or time-sensitive screening.

Highlights

► Auditory filter shapes were measured using ABRs and simultaneous notched noise in mice. ► ABR-derived filter bandwidths increased with increasing center frequency. ► The ABR notched noise method provides an efficient way to estimate auditory filter shape in mice.

Introduction

Mouse models have gained increasing importance for understanding the genetic and environmental contributions to the development of hearing function as well as the mechanisms underlying deafness and other hearing disorders. Basic hearing sensitivity is now routinely screened in mouse models of auditory function. However, common hearing screening protocols used in mice are often insensitive to detecting auditory dysfunction beyond elevated thresholds for sounds in quiet or reduced reactivity to loud sounds. Important information regarding auditory function may be missed when relying on these measures since animals can display significant deficits while maintaining normal pure tone thresholds (e.g., Kujawa and Liberman, 2009; Lauer and May, 2011; Allen and Ison, 2012; Satheesh et al., 2012).

Frequency resolution affects the ability to separate out components of complex sounds, detect sounds in background noise, and distinguish two sounds that are close together in frequency. Damage to the auditory system alters frequency resolution (e.g., Patterson et al., 1982; Tyler et al., 1984), contributing to common complaints of difficulty resolving sounds in the presence of competing backgrounds. Traditional behavioral measures of frequency selectivity are inefficient when considering animal models of developmental processes, early-onset hearing deficits, or models with rapidly declining hearing due to lengthy training and testing times. Our goal is to develop efficient, behaviorally validated methods to screen complex auditory functions in mice using rapidly measured evoked potentials. To that end, we describe a procedure using auditory brainstem responses (ABRs) measured in simultaneous spectrally notched noise to estimate peripheral frequency selectivity in mice.

The notched noise procedure characterizes frequency resolution based on the presentation of a pure tone in background noise containing a spectral notch (Fig. 1). According to the power spectrum model of masking, increasing the width of the notch results in less noise interference within an auditory filter until a “critical band” is reached where further increases in notch width no longer cause a change in threshold (Patterson, 1974). These theoretical auditory filters can be approximated using a rounded exponential (roex) minimization algorithm in order to estimate the critical bandwidth as an equivalent rectangular bandwidth (ERB) value (Glasberg and Moore, 1990). In the present paper, we evaluate the effectiveness of using the ABR and notched noise procedure as a rapid method for assessing auditory filter bandwidth in mice.

The notched noise procedure is based on well-established psychoacoustic behavioral methods that have only been implemented in a small sample of animals (Marean et al., 1993; Niemiec and Shoffner, 1990; Lin et al., 1997; Finneran et al., 2002; Lemmonds et al., 2012; May et al., 2006). Similar stimuli have been used in conjunction with ABRs to rapidly estimate auditory frequency selectivity in wild birds and dolphins (Popov et al., 1997; Gall and Lucas, 2010; Henry and Lucas, 2010a, Henry and Lucas, 2010b). This paradigm yields a reasonable estimate of auditory filters at a range of frequencies within several hours rather than the months to a year required for behavioral procedures. The ABR procedure is ideal for models that may be difficult to test behaviorally, show rapid auditory system degeneration, or require testing of many animals. Moreover, these tests can be repeated at multiple time points over the course of development, aging, or treatment.

Section snippets

Subjects

A total of 17 CBA/CaJ mice were bred and housed in a quiet vivarium to minimize exposure to potentially damaging environmental noise (Lauer et al., 2009). Ad libitum access to food and water was provided to all subjects. Ages of tested mice ranged from 6 to 28 weeks. Hearing status remains normal in this strain throughout this age range, and normal hearing was confirmed by measuring thresholds for clicks and tones presented in quiet for each test frequency. Seven mice were tested at each probe

Masked thresholds

ABR masked thresholds decreased with increasing notch width (Fig. 3A). As the spectral notch widened from a normalized deviation of 0.159–0.293, the ABR thresholds decreased for all three center frequencies tested. Inter-animal variability was noted to be greatest at a deviation of 0.159 for 8 and 16 kHz and 0.04 for 11.2 kHz. Quiet thresholds (not shown) were within the normal range for CBA/CaJ mice, but were approximately 15–25 dB higher than behavioral thresholds measured in the same strain (

Discussion

Behavioral measures used to estimate auditory filters with the notched noise paradigm are effective and sensitive for investigating auditory frequency selectivity, but these studies are limited to just a few species due to the length of time and expertise needed for animal training and testing. As an alternative, ABR procedures have been used to obtain auditory filter measurements in a matter of hours in birds and dolphins using the notched noise paradigm (Gall and Lucas, 2010; Henry and Lucas,

Summary

The ABR measurements using the notched noise method of estimating frequency resolution can be an efficient tool for researchers who wish to study more complex auditory functioning in mouse models. As to be expected, ABR-derived masked thresholds were slightly elevated compared to behavioral thresholds, but the general pattern of increased filter bandwidth (ERB) with increasing center frequency was consistent. The main advantage of using an ABR paradigm rather than a behavioral paradigm to

Acknowledgments

This research was supported by the National Organization for Hearing Research and NIH grants DC005211 and DC009353. The funding sources had no role in the study design; data collection, analysis, and interpretation; writing of the report; or the decision to submit the manuscript for publication. We thank Eric Young and Bradford May for discussions regarding the project, and Judy Park and Jessica Stuyvenberg for data collection assistance.

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