The suggestion has also been offered that the discrete biphasic pulses used in most cochlear implant stimulation strategies may assist in increased synchrony of the firing pattern of the auditory nerve (Rance, 2005). Period histograms of neural responses show that spikes in the action potential occur more often around the phase peak when using electrical stimulation than when using acoustic stimulation, for which the spikes are more spread out along the entire phase curve (Abbas, 1993). In addition the timing of the nerve response to electrical stimulation seems to be more precise and repeatable than it is for acoustic stimulation. It has also been shown that if a nerve fiber is stimulated electrically, both the growth of discharge rate and the maximum rate achievable are greater than when stimulating the nerve acoustically. For example, Zhou, Abbas, and Assouline (1995) demonstrated that electrical stimulation of demyelinated nerves in mice resulted in a measurable auditory brainstem response (ABR) waveform. If the pathology were localized to the spiral ganglion, there could be a problem with the entire auditory nerve not being excitable (Starr, Picton, & Kim, 2001).Įven assuming that the site of lesion was in fact in the auditory nerve, however, there were still reasons to at least consider the idea that cochlear implantation might be an effective intervention. Alternatively, if it were the axons that were the site of lesion, there would likely be at least a partial conduction block in the nerve that could reasonably be expected to worsen. In the case of a pathology that was demyelinating, the result could be desynchronous conduction of electrical stimulation across nerve fibers. There were logical bases for assuming that a cochlear implant would not be an appropriate or especially successful intervention for what the early ANSD researchers thought was hearing loss due to a neural degenerative condition. The recommendation echoes that made by the Joint Committee on Infant Hearing (2007), whose current position statement indicates that cochlear implantation should be given careful consideration for any child who experiences only limited benefit from appropriately fit amplification. ![]() At that time, it was often supposed that cochlear implants would not be a viable option for remediation in this population. This is a considerable departure from the first years after ANSD was identified and classified as a possible neural disorder (Sininger, Hood, Starr, Berlin, & Picton, 1995 Starr, Picton, Sininger, Hood, & Berlin, 1996). ![]() Another outcome was the recommendation that cochlear implantation be considered as a treatment option in the event of poor progress in auditory language development and speech understanding, regardless of behavioral audiometric thresholds. Among the many outcomes of the conference was a consensus to change the terminology used for referring to this particular type of hearing impairment to auditory neuropathy spectrum disorder (ANSD). The goal of the conference was to discuss a myriad of issues related to this auditory disorder, which is characterized by apparently normal outer hair cell function in combination with impaired or absent conduction of synchronous signals by the auditory nerve. ![]() In 2008, a group composed of audiologists, hearing scientists, medical geneticists, neonatologists, and neurologists met in Como, Italy, for the Guidelines and Development Conference on the Identification and Management of Children With Auditory Neuropathy.
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