Suppression tuning in noise-exposed rabbits

Abstract

Psychophysical, basilar-membrane (BM), and single nerve-fiber tuning curves, as well as suppression of distortion-product otoacoustic emissions (DPOAEs), all give rise to frequency tuning patterns with stereotypical features. Similarities and differences between the behaviors of these tuning functions, both in normal conditions and following various cochlear insults, have been documented. While neural tuning curves (NTCs) and BM tuning curves behave similarly both before and after cochlear insults known to disrupt frequency selectivity, DPOAE suppression tuning curves (STCs) do not necessarily mirror these responses following either administration of ototoxins [Martin et al., J. Acoust. Soc. Am. 104, 972-983 (1998)] or exposure to temporarily damaging noise [Howard et al., J. Acoust. Soc. Am. 111, 285-296 (2002)]. However, changes in STC parameters may be predictive of other changes in cochlear function such as cochlear immaturity in neonatal humans [Abdala, Hear. Res. 121, 125-138 (1998)]. To determine the effects of noise-induced permanent auditory dysfunction on STC parameters, rabbits were exposed to high-level noise that led to permanent reductions in DPOAE level, and comparisons between pre- and postexposure DPOAE levels and STCs were made. Statistical comparisons of pre- and postexposure STC values at CF revealed consistent basal shifts in the frequency region of greatest cochlear damage, whereas thresholds, Q10dB, and tip-to-tail gain values were not reliably altered. Additionally, a large percentage of high-frequency lobes associated with third tone interference phenomena, that were exhibited in some data sets, were dramatically reduced following noise exposure. Thus, previously described areas of DPOAE interference above f2 may also be studied using this type of experimental manipulation [Martin et al., Hear. Res. 136, 105-123 (1999); Mills, J. Acoust. Soc. Am. 107, 2586-2602 (2002)].

Distortion-product otoacoustic emission suppression tuning curves in hearing-impaired humans

“…These data share similarities with previously reported data but are not entirely consistent with other measures of DPOAE STCs in humans and other animals with cochlear damage (e.g., Gorga et al, 2003;Howard et al, 2002Howard et al, , 2003Porter et al, 2006;Martin et al, 1998;Abdala and Fitzgerald, 2003). For example, Martin et al (1998) noted sharper tuning of DPOAE STCs in rabbits following cochlear insult with the use of loop diuretics.…”

“…These differences existed when comparisons were made at the same sound pressure level (SPL), but were more pronounced when comparisons were made at the same sensation level (SL). DPOAE STCs in rabbits following temporary and/or permanent damage from noise exposure appeared to be insensitive to damage and, in some cases, the tip of the STC became more sharply tuned following cochlear insult (Howard et al, 2002(Howard et al, , 2003. Thus, in summary, it appears that measurements of DPOAE STCs in hearing-impaired ears are variable and do not consistently resemble the changes evident in more direct measurements of frequency selectivity in lower animals.…”

“…Presenting STCs on a logfrequency axis makes it easier to compare these functions across frequency, across subject groups, and across levels. It also may be useful in comparisons to previous data describing STCs, where data are typically plotted on a logfrequency scale (e.g., Kummer et al, 1995;Martin et al, 1987;Martin et al, 1998;Mills, 1998;Howard et al, 2002Howard et al, , 2003Abdala, 2005;Abdala and Fitzgerald, 2003;Abdala and Keefe, 2006;Gorga et al, 2002;Gorga et al, 2003;Gorga et al, 2008;Gorga et al, 2011b).…”

“…On the other hand, non-invasive DPOAE suppression measurements do not require training or active participation by the subject and can be made in infants and young children (Abdala, 2005;Abdala et al, 1996;Abdala and Chatterjee, 2003). DPOAE suppression measurements have also been used to estimate peripheral frequency selectivity in human adults and other animals with cochlear damage (Abdala and Fitzgerald, 2003;Howard et al, 2002Howard et al, , 2003Gorga et al, 2003;Martin et al, 1998). While DPOAE STCs in the normal auditory system reveal patterns that are similar to those seen in more direct measurements, DPOAE STCs in the presence of hearing loss do not always demonstrate patterns that are consistent with data obtained from invasive measurements in other animals.…”

Characterizing distortion-product otoacoustic emission components across four species

“…Finally, there is ample evidence for basal DPOAE sources in the literature (reviewed in Martin et al, 2010a) based upon DPOAE suppression tuning curves (Martin et al, 1999Howard et al, 2002Howard et al, , 2003, DPOAE onset latencies (Whitehead et al, 1996;Cone et al, 2009), and noise over-exposures (Avan et al, 1991(Avan et al, , 1995(Avan et al, , 1997 to name a few examples. In view of the results of prior studies, the demonstration of basal DPOAE components is not particularly surprising.…”