This study aimed to (1) characterize temporal response properties of the auditory nerve in implanted children with auditory neuropathy spectrum disorder (ANSD), and (2) compare results recorded in implanted children with ANSD with those measured in implanted children with sensorineural hearing loss (SNHL).
Participants included 28 children with ANSD and 29 children with SNHL. All subjects used cochlear nucleus devices in their test ears. Both ears were tested in 6 children with ANSD and 3 children with SNHL. For all other subjects, only one ear was tested. The electrically evoked compound action potential (ECAP) was measured in response to each of the 33 pulses in a pulse train (excluding the second pulse) for one apical, one middle-array, and one basal electrode. The pulse train was presented in a monopolar-coupled stimulation mode at 4 pulse rates: 500, 900, 1800, and 2400 pulses per second. Response metrics included the averaged amplitude, latencies of response components and response width, the alternating depth and the amount of neural adaptation. These dependent variables were quantified based on the last six ECAPs or the six ECAPs occurring within a time window centered around 11 to 12 msec. A generalized linear mixed model was used to compare these dependent variables between the 2 subject groups. The slope of the linear fit of the normalized ECAP amplitudes (re. amplitude of the first ECAP response) over the duration of the pulse train was used to quantify the amount of ECAP increment over time for a subgroup of 9 subjects.
Pulse train-evoked ECAPs were measured in all but 8 subjects (5 with ANSD and 3 with SNHL). ECAPs measured in children with ANSD had smaller amplitude, longer averaged P2 latency and greater response width than children with SNHL. However, differences in these two groups were only observed for some electrodes. No differences in averaged N1 latency or in the alternating depth were observed between children with ANSD and children with SNHL. Neural adaptation measured in these 2 subject groups was comparable for relatively short durations of stimulation (i.e., 11 to 12 msec). Children with ANSD showed greater neural adaptation than children with SNHL for a longer duration of stimulation. Amplitudes of ECAP responses rapidly declined within the first few milliseconds of stimulation, followed by a gradual decline up to 64 msec after stimulus onset in the majority of subjects. This decline exhibited an alternating pattern at some pulse rates. Further increases in pulse rate diminished this alternating pattern. In contrast, ECAPs recorded from at least one stimulating electrode in six ears with ANSD and three ears with SNHL showed a clear increase in amplitude over the time course of stimulation. The slope of linear regression functions measured in these subjects was significantly greater than zero.
Some but not all aspects of temporal response properties of the auditory nerve measured in this study differ between implanted children with ANSD and implanted children with SNHL. These differences are observed for some but not all electrodes. A new neural response pattern is identified. Further studies investigating its underlying mechanism and clinical relevance are warranted.
This study aimed to 1) characterize temporal response properties of the auditory nerve in implanted children with auditory neuropathy spectrum disorder (ANSD); and 2) compare results recorded in implanted children with ANSD with those measured in implanted children with sensorineural hearing loss (SNHL). Results of this study revealed differences in temporal response properties of the auditory nerve between subjects with ANSD and subjects with SNHL at some but not all electrode locations tested in this study. Patterns of increased amplitude over the course of the pulse train were observed in some subjects in both subject groups.
1Center for Hearing Research, Boys Town National Research Hospital, Omaha, Nebraska, USA; 2Department of Communication Sciences & Disorders, The University of Iowa, Iowa City, Iowa, USA; 3Department of Hearing and Speech, The Wake Forest Baptist Medical Center, Winston Salem, North Carolina, USA; and 4Department of Computer Science, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
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This work was supported by a grant from NIH/NIDCD (1R03DC013153).
Portions of this article were presented at the 20th World Congress of the International Federation of Oto-Rhino-Laryngological Societies, Seoul, Korea and the 8th International Symposium on Objective Measures in Auditory, Toronto, Canada.
The authors have no conflicts of interest to disclose.
Received September 23, 2014; accepted October 24, 2015.
Address for correspondence: Shuman He, Center for Hearing Research, Boys Town National Research Hospital, 555 North 30th Street, Omaha, NE 68131, USA. E-mail: Shuman.He@boystown.org