ReviewCortical development and neuroplasticity in Auditory Neuropathy Spectrum Disorder
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).
References (141)
- et al.
Speech perception and cortical auditory evoked potentials in cochlear implant users with auditory neuropathy spectrum disorders
Int. J. Pediatr. Otorhinolaryngol.
(2012) - et al.
Extracellular matrix and visual cortical plasticity: freeing the synapse
Neuron
(2004) - et al.
Auditory neuropathy/dyssynchrony its diagnosis and management
Pediatr. Clin. N. Am.
(2003) - et al.
Prevalence and risk factors for auditory neuropathy spectrum disorder in a screened newborn population at risk for hearing loss
Int. J. Pediatr. Otorhinolaryngol.
(2012) - et al.
Spontaneous firing as an epigenetic factor in brain development — physiological consequences of chronic tetrodotoxin and picrotoxin exposure on cultured rat neocortex neurons
Dev. Brain Res.
(1992) On the rate of maturation of sensory evoked potentials
Electroencephalogr. Clin. Neurophysiol.
(1988)- et al.
Electrophysiological correlates of progressive sensorineural pathology in carboplatin-treated chinchillas
Brain Res.
(2007) - et al.
Neural cell adhesion molecules in activity-dependent development and synaptic plasticity
Trends Neurosci.
(1996) Synaptic basis for developmental plasticity in somatosensory cortex
Curr. Opin. Neurobiol.
(2004)- et al.
Speech recognition in noise and presbycusis: relations to possible neural mechanisms
Hear Res.
(1997)