Age-related shifts in distortion product otoacoustic emissions peak-ratios and amplitude modulation spectra

Abstract

Amplitude modulation (AM) is an important temporal cue for precise speech and complex sound recognition. However, functional decline of the auditory periphery as well as degradation of central auditory processing due to aging can reduce the salience and resolution of temporal cues. Age-related deficits in central temporal processing have previously been observed at more rapid AM frequencies and various AM depths. These centrally observed changes result from cochlear changes compounded with changes along the ascending auditory pathway. In fact, a decrease in ability to detect temporally modulated sounds accurately could originate from changes in cochlear filtering properties and in cochlear mechanics due to aging. Nonetheless, few studies have examined cochlear mechanisms in AM detection. To assess integrity of the mechanical properties of the auditory periphery, distortion product otoacoustic emissions (DPOAEs) are a tool commonly used in clinics and in research. In this study, we measured DPOAEs to reveal age-related changes in peak f2/f1 ratio and degradation in AM detection by basilar membrane vibration. Two tones (f1 and f2, f2>f1) at various f2/f1 ratios and simultaneous presentation of one AM and one pure tone were used as stimuli to evoke DPOAEs. In addition of observing reduced DPOAE amplitudes and steeper slopes in the input-output DPOAE functions, higher peak f2/f1 ratios and broader f2/f1 tuning were also observed in aged animals. Aged animals generally had lower distortion product (DP) and first sideband (SB 1) responses evoked by an f1 pure tone and an f2 AM tone, regardless of whether the AM frequency was 45 Hz or 128 Hz. SB 1 thresholds, which corresponds to the smallest stimulus AM depth that can induce cochlear vibrations at the DP generator locus, were higher in aged animals as well. The results suggest that age-related changes in peak f2/f1 ratio and AM detection by basilar membrane vibration are consistent with a reduction in endocochlear potential and reduced prestin activity but with preserved hair cell bundle function. SB 1 responses evoked by f2 AM/f1 pure tone with various AM depths could serve as an estimate for cochlear AM detection. The sidebands of DP could also serve as additional physiological cues for detection of AM in the presence of other tone(s), even at typical conversational levels in speech.

Age-related changes in envelope-following responses at equalized peripheral or central activation

“…This is consistent with other work in aging [Sergeyenko et al, 2013, Parthasarathy et al, 2014, Möhrle et al, 2016] and noise exposure or tinnitus [Schaette and McAlpine, 2011, Möhrle et al, 2016, Hesse et al, 2016]. Decline in OHC function as measured by DPOAE will also play a role in auditory declines with aging [Lai and Bartlett, 2015, Sergeyenko et al, 2013] but does not appear to affect estimates of central gain [Verhulst et al, 2016] since all AN fibers would be affected. Although there are differences between aging and noise exposure, both can produce mixed OHC and IHC-AN damage, and the relative degree of that damage may affect individual changes in ABR and EFR measures [Bharadwaj et al, 2014, Verhulst et al, 2016, Zhong et al, 2014] and auditory nerve measures [Kale and Heinz, 2012].…”

“…Speech perceptual ability in noise has been found to correlate with ABR wave I amplitude as well [Bramhall et al, 2015]. In the auditory periphery, cochlear filter shapes and frequency specificity could be different between young and aged animals [May et al, 2006, Ananthakrishnan et al, 2016, Lai and Bartlett, 2015]. …”

“…The experimental protocols used for ABR and EFR recordings were similar to previously described details in Lai and Bartlett (2015), and Parthasarathy and Bartlett (2012). All auditory evoked potential recordings were performed in a 9’x9’ double-walled anechoic chamber (Industrial Acoustic Corporation).…”

Differences in postinjury auditory system pathophysiology after mild blast and nonblast acute acoustic trauma

“…A ground electrode was placed in the nape of the neck. These configurations are consistent with prior publications from our laboratory (Lai and Bartlett 2015;Bartlett 2011, 2012;Parthasarathy et al 2014). After electrode placement, electrode impedances were confirmed to be Ͻ1 k⍀ using a low-impedance amplifier (RA4LI; TDT).…”

“…Electromotility driven by prestin (a protein located on OHC wall; Dallos et al 2008;Liberman et al 2004) and mechanoelectrical transduction of stereocilia above the hair cells (Avan et al 2013;Kennedy et al 2005) are believed to be the two main active processes that produce DPOAE responses. All DPOAEs were performed in a 9-ft. ϫ 9-ft. doublewalled acoustic chamber (Industrial Acoustics Corporation) using standard techniques similar to those reported in Lai and Bartlett (2015). For anesthetization, animals were treated with 4% isoflurane via inhalation in an induction chamber.…”