Hearing Aids and the Brain

Hindawi Publishing Corporation International Journal of Otolaryngology Volume 2014, Article ID 518967, 5 pages http://dx.doi.org/10.1155/2014/518967 Editorial Hearing Aids and the Brain K. L. Tremblay,1 S. Scollie,2 H. B. Abrams,3 J. R. Sullivan,1 and C. M. McMahon4 1 Department of Speech and Hearing Sciences, University of Washington, Seattle, WA 98105, USA University of Western Ontario, London, ON, Canada N6A 3K7 3 Starkey Hearing Technologies, Eden Prairie, MN 55344, USA 4 Centre for Language Sciences, Australian Hearing Hub, 16 University Dve, Macquarie University, North Ryde, NSW 2109, Australia 2 Correspondence should be addressed to K. L. Tremblay; Received 12 December 2013; Accepted 29 May 2014; Published 3 September 2014 Copyright © 2014 K. L. Tremblay et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. At the heart of most rehabilitation programs for people with hearing loss is the use of amplification. The purpose of hearing aid amplification is to improve a person’s access to sound. Depending on the degree and configuration of the individual’s hearing loss, the hearing aid is tasked with increasing sound levels at different frequency regions to ensure that incoming speech frequencies are reaching the ear at sufficient levels to compensate for the individual’s hearing loss. However, a perceptual event is dependent not only on the audibility of the signal at the level of the ear, but also on how that sound is biologically coded, integrated, and used. As described by Tremblay and Miller in this special issue, this complex ear-brain neural network system starts with sound leaving the hearing aid. At this stage the acoustics of the amplified signal has been altered by the hearing aid. It is this modified signal that is being encoded at subsequent stages of processing: the ear, brainstem, midbrain, and the cortex. The integrity of the signal, and the biological codes, are therefore assumed to contribute to the resultant perceptual event and it is for this reason that the brain can be considered an essential component to rehabilitation. Yet, little is known about how the brain processes amplified sound or how it contributes to perception and the successful use of hearing aid amplification (see Figure 1). The intent of this IJO special edition is to integrate neuroscience and clinical practice to advance hearing health care. Such lines of inquiry can spawn new insight into stimulationrelated brain plasticity that might, in turn, help explain why some individuals (but not others) report increased speech understanding while wearing their devices. From a clinical perspective, there is interest in determining if measures of brain activity might be of use to the clinician, during hearing aid selection and fitting, as well as to the engineers who are designing the instruments. However, to move forward, there are unresolved issues that can appear conflicting to the clinician and/or scientist who wish to embark in new research directions or clinical services. For this reason, a call for papers on the topic of Hearing Aids and the Brain was made in an effort to define converging evidence. What resulted is a collection of papers from different laboratories that identify caveats and concerns, as well as potential opportunities. The collection of papers addresses two main questions: (1) Is it possible to use brain measures to determine a person’s neural detection of amplified sound? (2) Can brain measures provide information about how the brain is making use of this amplified sound? Before we summarize the answers to the questions, it’s important to review the framework for including objective measures to examine the neural representation of amplified sound. When a person is fitted with a hearing aid, there are two categories of test procedures involved in the process: (i) behavioral measures, which require active participation by the patient (e.g., pure-tone threshold estimation, speech testing, and self-report questionnaires), and (ii) objective measures, where subjective responses are not required (e.g., probe microphone electroacoustics and unaided electrophysiology). Here we expand the use of electrophysiology to determine if brain measures can be used as an objective measure to estimate aided thresholds and/or quantify hearing aid transduced signals in the brain for the purpose 2 International Journal of Otolaryngology Figure 1 of guiding device fitting and/or to assess suprathreshold representation of amplified auditory signals in the brain to estimate perceptual performance and/or the related cognitive resources involved. This expanded use of objective measures is relevant to patients of all ages but is particularly germane to the pediatric population where the use of behavioral tools is limited. As described by L. M. Jenstad et al. in this issue, behavioral threshold information is not usually available before age 6 months (and often later), speech testing is unavailable, and subjective questionnaires are limited to caregiver observation of behaviors. Thus, there is greater reliance on objective procedures to measure the effects of amplification beyond the tympanic membrane in infants and young children. One such measure is the use of auditory evoked potentials (AEPs). The use of AEPs to aid in clinical assessment is not new. Click-evoked auditory brainstem responses were tried long ago to estimate unaided and aided thresholds in infants and young children. However they proved to be unsuccessful because the short duration signal (click, tone-pip) interacted with the hearing aid circuitry in a way that introduced ringing and other artifacts [1]. In this special issue, S. Anderson and N. Kraus reintroduce the concept of using complex speech evoked ABRs (also called the frequency following response (FFR)) and provide a case study to show that it is possible to record FFRs while a person is wearing a hearing aid. But FFR and speech evoked ABR research is still in its infancy. It will become necessary to define the interactions that take place between the instrument and brainstem responses, especially in people with hearing loss and who wear hearing aid devices to determine if some of the obstacles encountered when recording cortical evoked potentials (CAEPs) also apply to the FFR. There is much literature exploring the role of CAEPs in assessing people with hearing loss, but the inclusion of people with hearing loss who wear hearing aids is still quite sparse. In this special issue, investigators from different laboratories describe some of caveats and concerns when measuring evoked CAEPs in combination with hearing aid amplification. L. M. Jenstad et al. showed that CAEPs (P1-N1-P2) do not reliably reflect hearing aid gain, even when different types of hearing aids (analog and digital) and t (...truncated)