Stapes Vibration in the Chinchilla Middle Ear: Relation to Behavioral and Auditory-Nerve Thresholds

Abstract

The vibratory responses to tones of the stapes and incus were measured in the middle ears of deeply anesthetized chinchillas using a wide-band acousticstimulus system and a laser velocimeter coupled to a microscope. With the laser beam at an angle of about 40°relative to the axis of stapes piston-like motion, the sensitivity-vs.-frequency curves of vibrations at the head of the stapes and the incus lenticular process were very similar to each other but larger, in the range 15-30 kHz, than the vibrations of the incus just peripheral to the pedicle. With the laser beam aligned with the axis of pistonlike stapes motion, vibrations of the incus just peripheral to its pedicle were very similar to the vibrations of the lenticular process or the stapes head measured at the 40°angle. Thus, the pedicle prevents transmission to the stapes of components of incus vibration not aligned with the axis of stapes piston-like motion. The mean magnitude curve of stapes velocities is fairly flat over a wide frequency range, with a mean value of about 0.19 mm . (s Pa −1 ), has a high-frequency cutoff of 25 kHz (measured at −3 dB re the mean value), and decreases with a slope of about −60 dB/octave at higher frequencies. According to our measurements, the chinchilla middle ear transmits acoustic signals into the cochlea at frequencies exceeding both the bandwidth of responses of auditory-nerve fibers and the upper cutoff of hearing. The phase lags of stapes velocity relative to ear-canal pressure increase approximately linearly, with slopes equivalent to pure delays of about 57-76 μs.

The chinchilla animal model for hearing science and noise-induced hearing loss

“…This advantage has led to a breadth of detailed published data on normal middle-ear and cochlear function, device development, and the effects of conductive and peripheral hearing losses (Martin, 2012). The readily accessible middle-ear space and cochlea allow for complex experimental manipulations to quantify sound transmission through the middle ear and into the cochlea (Rosowski et al , 2006; Slama et al , 2010; Ravicz and Rosowski, 2013; Robles et al , 2015; Wang and Gan, 2016; Peacock et al , 2018). Furthermore, easy cochlear accessibility allowed for thorough and rigorous characterizations of cochlear-nonlinearity properties (i.e., level-dependent gain and bandwidth effects in basilar-membrane responses) to be collected following delicate microsurgical procedures that can easily damage the normal function of the cochlea (Robles et al , 1997; Ruggero et al , 1997; Rhode and Recio, 2000).…”

Mapping the phase and amplitude of ossicular chain motion using sound-synchronous optical coherence vibrography

“…The he speaker) so TM and three l and the wall a itude. n can be ether with mbo with nce arises observed nce of ~5 ); the rest o the TM, and phase the stapes (green square 75%) than the incus and stap additional del than ~8 kHz, delay of the m difference be increase can measurements consistent wit [5,9]. Figure 6 show frequencies: 3 with the stim vibration patt phase maps indicating stan presence of measurements ) e tion view um of the the stapes anal bone from the Fig.…”

“…Modern investigations are generally conducted using more sensitive optical interferometric techniques, particularly laser Doppler vibrometry (LDV) and holography [6][7][8]. LDV and holography are surface measurement techniques and, therefore, require surgical preparation to access structures beyond the TM [9]. They are also subject to artefacts caused by other vibrating structures located behind the tissue of interest if those structures are sufficiently reflective [10].…”

Frequency sensitivity in mammalian hearing from a fundamental nonlinear physics model of the inner ear

“…This led these authors to conclude that the inner ear could have “a crucial role in setting the frequency limits..” but that “It remains to be seen whether the finding that the bandwidth of middle-ear vibrations exceeds that of the audiogram in chinchilla, gerbil, guinea pig, horseshoe bat, pigeon, and turtle will be confirmed..” 3 . A number of subsequent biological measurements and finite element simulations seem to support the lack of frequency specificity of the outer and middle ear (e.g., refs 23 , 24 and 25 , respectively). For the reader’s convenience, data underlying this view are presented for the example of the Gerbil’s hearing system in our Suppl.…”

“…7 and the discussion in ref. 24 ); the main role in shaping hearing sensitivity seems to be commonly still attributed to the outer and middle ear.…”