Elsevier

Hearing Research

Volume 330, Part B, December 2015, Pages 221-232
Hearing Research

Review
Cortical development and neuroplasticity in Auditory Neuropathy Spectrum Disorder

https://doi.org/10.1016/j.heares.2015.06.001Get rights and content

Highlights

  • Cortical developmental patterns in ANSD reflect severity of neural dys-synchrony.

  • Sensitive periods for central auditory development affect outcomes in ANSD.

  • Cortical neuroplasticity predicts success with clinical intervention in ANSD.

Abstract

Cortical development is dependent to a large extent on stimulus-driven input. Auditory Neuropathy Spectrum Disorder (ANSD) is a recently described form of hearing impairment where neural dys-synchrony is the predominant characteristic. Children with ANSD provide a unique platform to examine the effects of asynchronous and degraded afferent stimulation on cortical auditory neuroplasticity and behavioral processing of sound. In this review, we describe patterns of auditory cortical maturation in children with ANSD. The disruption of cortical maturation that leads to these various patterns includes high levels of intra-individual cortical variability and deficits in cortical phase synchronization of oscillatory neural responses. These neurodevelopmental changes, which are constrained by sensitive periods for central auditory maturation, are correlated with behavioral outcomes for children with ANSD. Overall, we hypothesize that patterns of cortical development in children with ANSD appear to be markers of the severity of the underlying neural dys-synchrony, providing prognostic indicators of success of clinical intervention with amplification and/or electrical stimulation.

This article is part of a Special Issue entitled <Auditory Synaptology>.

Section snippets

Auditory Neuropathy Spectrum Disorder (ANSD): description and background

Among auditory disorders, auditory neuropathy is a relatively recently discovered condition (Starr et al., 1991, Starr et al., 1996). A hallmark of Auditory Neuropathy Spectrum Disorder (ANSD) is the vast inter and intra-subject variability which defines its patient population. This variability has lead to historically different classifications or nomenclatures for ANSD (Rapin and Gravel, 2006). The disorder was first described and titled Auditory Neuropathy by Starr et al. (1996). However, to

Similarities in pathophysiology between SNHL and ANSD

Though SNHL and ANSD may be thought of as entirely distinct disorders of the auditory system, in reality, there may be significant overlap between these clinical diagnoses. That is, SNHL, which may traditionally be categorized as an inner ear disorder whose primary manifestation is related to elevated auditory thresholds, may be also characterized by neurodegenerative, synaptic, and neural firing pattern deficits (Kujawa and Liberman, 2006, Kujawa and Liberman, 2009, Gourévitch et al., 2014,

How might VIII nerve dys-synchrony alter the central auditory system?

A commonly held tenet of neuroscience is that deprivation of normal stimulation of sensory cortices has the potential to cause maturational abnormalities (see Pallas, 2001 for a review). Many may think of deprivation as the overall lack or absence of stimulation. Indeed, this type of deprivation has the ability to alter development (e.g., Wiesel and Hubel, 1963, Hubel and Wiesel, 1970). For example, Sharma et al., 2002a, Sharma et al., 2002b, Sharma et al., 2002c, Sharma et al., 2005b, Sharma

Patterns of cortical development in ANSD

Because of the potential for altered neuroplasticity, it is imperative that central auditory development be evaluated and monitored in patients with hearing impairment, including those with ANSD. One non-invasive methodology that can perform this function in humans is cortical auditory evoked potentials (CAEP). These EEG measurements can provide a window into the development of the central auditory system by recording the auditory cortex's responses to sound. In normal hearing individuals, the

Cortical maturation and behavioral outcome

Recent studies from our laboratory and other laboratories (Rance et al., 2002, Michalewski et al., 2005, Sharma et al., 2011, Alvarenga et al., 2012, Cardon and Sharma, 2013), have found that cortical development and functioning is a strong predictor of behavioral outcome. For example, Sharma et al., 2011 and Cardon and Sharma 2013 reported that behavioral outcome was significantly different between children with ANSD who had normal, delayed, and abnormal P1 CAEP responses such that performance

Cortical changes after intervention with amplification and/or electrical stimulation

There exists some debate regarding the most effective course of treatment for patients with ANSD. While some people advocate the use of conventional acoustic amplification via hearing aids, citing studies in which hearing aids have appeared to provide benefit to some with ANSD (e.g., Rance et al., 2002, Sharma et al., 2011, Cardon et al., 2012), others disagree (e.g., Berlin et al., 1998, Hood, 1998). In one of our recent studies (Sharma et al., 2011), we concluded that though hearing aids did

Clinical implications

Many children with ANSD are diagnosed very early in life, due to physiologic diagnostic testing procedures available to clinicians (i.e., ABR, OAEs). However, beyond diagnosis, very little can be done to evaluate or treat infants and young children with ANSD. This obstacle stems, to a large degree, from the current need for behavioral audiometric thresholds in hearing aid fitting. Thus, clinicians often wait for several months after a child is old enough to participate in behavioral audiometry

Summary and conclusions

Though ANSD is a relatively recently discovered auditory disorder, advances in our understanding of the underlying pathophysiology, evaluation, and management of patients with ANSD have occurred over the past several years. CAEPs have contributed significantly to this understanding by providing a window into central auditory function and maturation in individuals with ANSD. Additionally, recent reports in subjects with SNHL have made it evident that ANSD and SNHL may overlap more than

Acknowledgments

Research supported by grants from the National Institutes of Health-National Institute of Deafness and Other Communication Disorders (NIH-NIDCD) to A.S. (R01DC0625) and G.C. (F31 DC013218-01A1).

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