Structures that contribute to middle-ear admittance in chinchilla

Abstract

We describe measurements of middle-ear input admittance in chinchillas (Chinchilla lanigera) before and after various manipulations that define the contributions of different middle-ear components to function. The chinchilla's middle-ear air spaces have a large effect on the lowfrequency compliance of the middle ear, and removing the influences of these spaces reveals a highly admittant tympanic membrane and ossicular chain. Measurements of the admittance of the air spaces reveal that the high-degree of segmentation of these spaces has only a small effect on the admittance. Draining the cochlea further increases the middle-ear admittance at low frequencies and removes a low-frequency (less than 300 Hz) level dependence in the admittance. Spontaneous or sound-driven contractions of the middle-ear muscles in deeply anesthetized animals were associated with significant changes in middle-ear admittance. KeywordsMiddle-ear structure-function; Comparative Auditory Function INTRODUCTIONChinchillas (Chinchilla lanigera) are nocturnal foragers that lived in communal burrows and are native to the rocky slopes of the high Andes. However, wild chinchillas are endangered, having been over-hunted by humans for food and their fur, and preyed upon by European species introduced into their habitat. Captive chinchillas have been successfully bred in the USA and Russia over the last 80 years. Since the 1950s, chinchillas have become a common animal model in hearing and other research areas (Price 1953;Tibbitts and Hillemann 1959);Peters 1965;Henderson 1969;Lupien and McCay 1960; Bismark and Pfeiffer 1967;Trautwein & Helmboldt 1967;Strike and Seigneur 1969;Dallos 1970;Miller 1970).The high Andes is an open and arid environment and chinchillas show some adaptations that are similar to those seen in other animals adapted to open and arid areas including a few distinctive features of the middle ear:1. large middle-ear air spaces ( total volume ≥ 1.5 cc) that are segmented into multiple sub-cavities (Browning and Granish 1978; Vrettakkos et al. 1988).Corresponding Author: John J Rosowski, Email: John_Rosowski@meei.harvard.edu, Phone: 1 617 657 4237, Fax 1 617 720 4408. 2. large tympanic-membrane (TM) and ossicular dimensions for an animal of its size (Vrettakkos et al. 1988; Rosowski 1991a&b, 1994, and 3. increased mechanical sensitivity to low-frequency (f < 1000 Hz) acoustic stimuli relative to other animals with similar hearing ranges (Ruggero et al. 1990). NIH Public AccessWhen viewed in light of the relatively sensitive low-frequency auditory thresholds in this species (Fay 1988;Miller 1970), the chinchilla middle ear appears specialized for lowfrequency hearing. While preliminary acoustic admittance (Dear 1987) 1 , cochlear potential (Dallos 1970) and ossicular-motion measurements (Ruggero et al. 1990) are all consistent with this view, past studies have not determined which middle-ear structures contribute to the sensitivity to low-frequency sound.There is a history of work on other species specialized for arid climates,...

Transmission matrix analysis of the chinchilla middle ear

“…Minor deviations in linearity were observed near 160 Hz. These deviations are consistent with previous work (Ruggero et al, 1996;Rosowski et al, 2006;Songer and Rosowski, 2006) and are usually attributed to an inner ear nonlinearity.…”

“…The stimulus we used was a train of 100 log chirps with frequency components between 11 Hz and 24 kHz. The stimulus was generated with a series of LabView scripts and presented to the ear with a hearing-aid earphone (Knowles ED-1913) that was part of a sound-source/measurement assembly with a high acoustic output impedance (Ravicz et al, 1992;Rosowski et al, 2006). A hearing-aid microphone (Knowles EK-3027) was built into the sound source/measurement assembly and used to measure the resultant sound pressure in the ear canal.…”

Middle ear function and cochlear input impedance in chinchilla

“…8͑B͔͒ and there is no evidence of a roll-off at these frequencies. The more-or-less pronounced notch separating the two lobes in the animal data described above is likely due to a resonance between the bulla and the open hole in the bullar wall ͑e.g., Møller, 1965;Ravicz et al, 1992;Rosowski et al, 2006͒. The phases of G ME in these species have similarities in shape, but the decrease with frequency varies across species ͑fastest for the cat and slowest for the gerbil͒. The average group delay between 0.2 and 10 kHz is about 52 s in our study, 131 s in cat, 51 s in gerbil, 82 s in guinea pig, and 92 s in human.…”

Morphology and function of Neandertal and modern human ear ossicles

“…ITRs are simple but straightforward estimates for understanding the impedance matching function of the middle ear (33,40). Although ITRs do not result in an accurate prediction of auditory sensitivity levels of the entire hearing range, they can be seen as an approximation for the pressure gain achieved by the middle ear at lower frequencies (33).…”