Dau, Torsten

Encina-Llamas, Gerard

Epp, Bastian

M. Harte, James

Hearing impairment (HI) has traditionally been defined according to an increase in pure-tone threshold as measured by an audiogram. There is, however, emerging evidence that just evaluating threshold sensitivity does not fully characterize functional deficits in auditory processing. Recent animal studies have shown that noise over-exposure can cause loss of auditory nerve fiber (ANF) synapses — known as deafferentation (see Kujawa and Liberman (2015) for a review) — without causinghair cell loss. Furman et al., (2013) reported that deafferentation occurs predominantly to low-spontaneous rate (low-SR) fibers, which have higher thresholds and therefore respond to higher acoustic intensities. Consequently, these ANF synapse losses do not alter detection of thresholds, but do degrade the encoding of supra-threshold sounds. The loss of ANF synapses might be a primary neural degeneration that precedes both hair cell and ANF cell body loss (Kujawa and Liberman, 2015

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Downloaded from orbit.dtu.dk on: Aug 03, 2018Using auditory steady-state responses to evaluate auditory nerve integrity in normal-hearing and mild hearing-impaired listenersEncina-Llamas, Gerard; Dau, Torsten; M. Harte, James; Epp, BastianPublication date:2016Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Encina-Llamas, G., Dau, T., M. Harte, J., & Epp, B. (2016). Using auditory steady-state responses to evaluateauditory nerve integrity in normal-hearing and mild hearing-impaired listeners. Poster session presented at 39thmidwinter meeting of Association of Research in Otolaryngology, San Diego, CA, United States.Using auditory steady-state responses to evaluate auditory nerveintegrity in normal-hearing and mild hearing-impaired listenersGerard Encina-Llamas1, Torsten Dau1, James M. Harte2 and Bastian Epp11 Hearing Systems, Department of Electrical Engineering, Technical University of Denmark - 2 Interacoustics Research UnitIntroductionHearing impairment (HI) has traditionally been defined ac-cording to an increase in pure-tone threshold as measuredby an audiogram. There is, however, emerging evidence thatjust evaluating threshold sensitivity does not fully characterizefunctional deficits in auditory processing. Recent animal studieshave shown that noise over-exposure can cause loss of auditorynerve fiber (ANF) synapses — known as deafferentation (seeKujawa and Liberman (2015) for a review) — without causinghair cell loss. Furman et al., (2013) reported that deafferenta-tion occurs predominantly to low-spontaneous rate (low-SR)fibers, which have higher thresholds and therefore respond tohigher acoustic intensities. Consequently, these ANF synapselosses do not alter detection of thresholds, but do degrade theencoding of supra-threshold sounds. The loss of ANF synapsesmight be a primary neural degeneration that precedes bothhair cell and ANF cell body loss (Kujawa and Liberman, 2015).ASSR are gross electroencephalography (EEG) potentialsthat follow the envelope of periodic acoustic stimuli.• ASSR magnitudes grow monotonically and compressively(slopes lower than 1) with increasing stimulation level(Encina-Llamas et al., in press).• It is suggested in the present study that ASSR growth-levelfunctions may be a potential tool to evaluate ANF integrity.Hypothesis• ASSR growth-level functions with shallow modulation(m=25%) have similar slopes as ASSR functions with highmodulation (m=85%) but with lower magnitudes.• For preferential low-SR deafferentation: ASSR magnitudes forshallow modulation depths are reduced for higher stimula-tion levels, diverging from typically non-deafferentated level-curves.High-SRMedium-SRLow-SRFig.1 Hypothesized ASSR growth-level functions for audiometrically normal-hearing lis-teners when using sinusoidally amplitude modulated (SAM) tones with full modulation(blue trace), shallow modulation (red trace), and shallow modulations in the presence ofdeafferentation (yellow trace). See Bharadwaj et al., (2014)Methods- ƒc: 2 kHz @ ƒm: 93 Hz- m: 85%, 25%- Levels: 34 to 87 dB SPL- Subjects: 9 young NH listen-ers (3 females). 4 mild HI lis-teners (1 female) impaired atCF≥ 4 kHz- Equipment: Biosemi Ac-tiveTwo EEG system. Soundpresented via ER-3 earphonesmounted on an ER-10B+ OAEprobe 0.125 0.25 0.5 1 2 3 4 6 8Frequency [kHz]10010203040Hearing level [dB HL]Hearing-impairedNormal-hearingResults55504540353025201510ASSR magnitude  (dB re. 1 µV)subj = ando90 subj = enes92 subj = kaov87 subj = suan9055504540353025201510ASSR magnitude  (dB re. 1 µV)subj = geas86 subj = mava91 subj = ikpo90 subj = anni9155504540353025201510ASSR magnitude  (dB re. 1 µV)subj = jeen5430 40 50 60 70 80 90Stimulus level [dB SPL]subj = jeng6430 40 50 60 70 80 90Stimulus level [dB SPL]subj = bjen5130 40 50 60 70 80 90Stimulus level [dB SPL]subj = adno8530 40 50 60 70 80 90Stimulus level [dB SPL]55504540353025201510ASSR magnitude  (dB re. 1 µV)subj = maer49ASSR m=85%. SignificantASSR m=85%. Non-significantASSR m=85%. Background noiseASSR m=25%. SignificantASSR m=25%. Non-significantASSR m=25%. Background noiseFig. 2: ASSR growth-level functions in all recorded subjects (A) and simplified trendsfor each of the arbitrarily clustered group of subjects (B-D). Solid symbols repre-sent statistically significant data points (F-test, p<1%), open symbols show statisti-cally non-significant results. ASSR magnitudes obtained using high modulation depths(m=85%) are shown as blue circles and ASSR magnitudes using shallow modulationdepths (m=25%) are shown as red circles. Thin continuous lines represent the esti-mated background noise for each of the recorded functions. The plot background colorgroups the individual subjects as normal-hearing, NH (green), normal-hearing showingan uncommon behaviour, NH? (yellow), and mild-hearing-impaired (mild-HI).A30 40 50 60 70 80 90Stimulus level [dB SPL]55504540353025201510ASSR magnitude  (dB re. 1 µV)Group NHASSR m=85%ASSR m=25%B30 40 50 60 70 80 90Stimulus level [dB SPL]55504540353025201510ASSR magnitude  (dB re. 1 µV)Group NH?ASSR m=85%ASSR m=25%C30 40 50 60 70 80 90Stimulus level [dB SPL]55504540353025201510ASSR magnitude  (dB re. 1 µV)Group mild-HIASSR m=85%ASSR m=25%. SignificantASSR m=25%. Non-significantDDiscussionAll NH NH? mild-HISubject group45403530252015Estimated intercept [dB]m=25%m=85%(∗∗∗) (∗∗∗) (∗∗∗) (∗∗∗)NH NH? mild-HISubject group0.100.050.000.050.100.150.200.250.300.35Estimated slope [dB/dB]m=25%m=85%(∗∗∗)A mixed model post-hoc analysis revealed that:• ASSR magnitudes are statistically different for each modula-tion depth, both in the whole dataset and within each of thethree arbitrary subject groups.• Slopes estimates for modulation high and shallow modula-tions in the mild-HI group are statistically different, but not inthe other groups.theFuture work• For shallow modulation and levels above 60 dB SPL, it ap-pears that ASSR magnitudes are reduced for the mild-HLgroup when compared with the NH group. For the NH? group,ASSR growth-level functions seem to reduce initially but fullyrecover at very high stimulus levels, i.e. non-monotonic.• The effects of off-frequency contributions to the ASSR at highstimulus intensities and the test-retest variability intrinsic tophysiological signals need to be investigated. It is inappropri-ate to speculate on the potential effect size of deafferenta-tion until more data is available, so it is vital to minimiseother factors that could confound the interpretation of ASSRgrowth-level curves.• A phenomenological model can be used to disentangle thepossible contributing factors to the ASSR growth-level func-tions. The relative loss of the different groups of SR fibers,the degree of deafferentation, and the off-frequency contri-butions at a cochlear level will be investigated.Conclusion• ASSR growth-level functions obtained at shallow modulationdepths show different slopes in non-impaired frequencies inNH and mild-HI listeners.• ASSR growth-level function have the potential tool to evalu-ate the integrity of the peripheral hearing system at supra-threshold levels.ACKNOWLEDGMENTThis work was founded by the Oticon Center of Excellence for Hearing and SpeechSciences (CHeSS) at the Technical University of Denmark (DTU).REFERENCESBharadwaj et al. (2014). Cochlear neuropathy and the coding of supra-thresholdsound. Front Syst Neurosci. 8:26.Encina-Llamas et al. (in press). Evaluation of peripheral compression and auditorynerve fiber intensity coding using auditory steady-state responses. ISAAR 2015.Furman et al. (2013). Noise-induced cochlear neuropathy is selective for fibers withlow spontaneous rates. J. Neurophysiol. 110(3):577-86.Kujawa and Liberman (2015). Synaptopathy in the noise-exposed and aging cochlea:Primary neural degeneration in acquired sensorineural hearing loss. Hearing Res.330:191-199.

Using auditory steady-state responses to evaluate auditory nerve integrity in normal-hearing and mild hearing-impaired listeners

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Using auditory steady-state responses to evaluate auditory nerve integrity in normal-hearing and mild hearing-impaired listeners

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