scholarly journals Noise-induced cochlear neuropathy is selective for fibers with low spontaneous rates

2013 ◽  
Vol 110 (3) ◽  
pp. 577-586 ◽  
Author(s):  
Adam C. Furman ◽  
Sharon G. Kujawa ◽  
M. Charles Liberman
Keyword(s):  
Auditory Nerve ◽  
Dynamic Range ◽  
Frequency Tuning ◽  
Nerve Fibers ◽  
Sensory Cells ◽  
High Threshold ◽  
Distortion Product ◽  
Selective Loss ◽  
Brainstem Response ◽  
Auditory Nerve Fibers

Acoustic overexposure can cause a permanent loss of auditory nerve fibers without destroying cochlear sensory cells, despite complete recovery of cochlear thresholds ( Kujawa and Liberman 2009 ), as measured by gross neural potentials such as the auditory brainstem response (ABR). To address this nominal paradox, we recorded responses from single auditory nerve fibers in guinea pigs exposed to this type of neuropathic noise (4- to 8-kHz octave band at 106 dB SPL for 2 h). Two weeks postexposure, ABR thresholds had recovered to normal, while suprathreshold ABR amplitudes were reduced. Both thresholds and amplitudes of distortion-product otoacoustic emissions fully recovered, suggesting recovery of hair cell function. Loss of up to 30% of auditory-nerve synapses on inner hair cells was confirmed by confocal analysis of the cochlear sensory epithelium immunostained for pre- and postsynaptic markers. In single fiber recordings, at 2 wk postexposure, frequency tuning, dynamic range, postonset adaptation, first-spike latency and its variance, and other basic properties of auditory nerve response were all completely normal in the remaining fibers. The only physiological abnormality was a change in population statistics suggesting a selective loss of fibers with low- and medium-spontaneous rates. Selective loss of these high-threshold fibers would explain how ABR thresholds can recover despite such significant noise-induced neuropathy. A selective loss of high-threshold fibers may contribute to the problems of hearing in noisy environments that characterize the aging auditory system.

Frequency Tuning and Spontaneous Activity in the Auditory Nerve and Cochlear Nucleus Magnocellularis of the Barn Owl Tyto alba

1997 ◽  
Vol 77 (1) ◽  
pp. 364-377 ◽  
Author(s):  
Christine Köppl
Keyword(s):  
Response Latency ◽  
Cochlear Nucleus ◽  
Auditory Nerve ◽  
Frequency Tuning ◽  
Barn Owl ◽  
Nerve Fibers ◽  
Spontaneous Discharge ◽  
Tyto Alba ◽  
Nucleus Magnocellularis ◽  
Auditory Nerve Fibers

Köppl, Christine. Frequency tuning and spontaneous activity in the auditory nerve and cochlear nucleus magnocellularis of the barn owl Tyto alba. J. Neurophysiol. 77: 364–377, 1997. Single-unit recordings were obtained from the brain stem of the barn owl at the level of entrance of the auditory nerve. Auditory nerve and nucleus magnocellularis units were distinguished by physiological criteria, with the use of the response latency to clicks, the spontaneous discharge rate, and the pattern of characteristic frequencies encountered along an electrode track. The response latency to click stimulation decreased in a logarithmic fashion with increasing characteristic frequency for both auditory nerve and nucleus magnocellularis units. The average difference between these populations was 0.4–0.55 ms. The most sensitive thresholds were ∼0 dB SPL and varied little between 0.5 and 9 kHz. Frequency-threshold curves showed the simple V shape that is typical for birds, with no indication of a low-frequency tail. Frequency selectivity increased in a gradual, power-law fashion with increasing characteristic frequency. There was no reflection of the unusual and greatly expanded mapping of higher frequencies on the basilar papilla of the owl. This observation is contrary to the equal-distance hypothesis that relates frequency selectivity to the spatial respresentation in the cochlea. On the basis of spontaneous rates and/or sensitivity there was no evidence for distinct subpopulations of auditory nerve fibers, such as the well-known type I afferent response classes in mammals. On the whole, barn owl auditory nerve physiology conformed entirely to the typical patterns seen in other bird species. The only exception was a remarkably small spread of thresholds at any one frequency, this being only 10–15 dB in individual owls. Average spontaneous rate was 72.2 spikes/s in the auditory nerve and 219.4 spikes/s for nucleus magnocellularis. This large difference, together with the known properties of endbulb-of-Held synapses, suggests a convergence of ∼2–4 auditory nerve fibers onto one nucleus magnocellularis neuron. Some auditory nerve fibers as well as nucleus magnocellularis units showed a quasiperiodic spontaneous discharge with preferred intervals in the time-interval histogram. This phenomenon was observed at frequencies as high as 4.7 kHz.

Effect of electrical stimulation of the crossed olivocochlear bundle on auditory nerve response to tones in noise

1987 ◽  
Vol 57 (4) ◽  
pp. 1002-1021 ◽  
Author(s):  
R. L. Winslow ◽  
M. B. Sachs
Keyword(s):  
Auditory Nerve ◽  
Noise Level ◽  
Dynamic Range ◽  
Response Rate ◽  
Discharge Rate ◽  
Nerve Fibers ◽  
Range Shift ◽  
Auditory Nerve Fiber ◽  
Auditory Nerve Fibers ◽  
Rate Suppression

The discharge rates of single auditory-nerve fibers responding to best-frequency (BF) tones of varying level presented simultaneously with fixed level broadband noise were recorded with and without electrical stimulation of the crossed olivocochlear bundle (COCB). In the absence of COCB stimulation, monotonic increases in noise level produce monotonic increases in the low-level noise-driven response rate of auditory nerve fibers. As a result of adaptation, these increases in noise-driven response rate produce monotonic decreases in saturation discharge rate. At high noise levels, these compressive effects may eliminate the differential rate response of auditory nerve fibers to BF tones. COCB stimulation can restore this differential rate response by producing large decreases in noise-driven response rate and large increases in saturation discharge rate. In backgrounds of quiet, COCB stimulation is known to shift the dynamic range of single auditory nerve fiber BF tone responses to higher stimulus levels. In the presence of background noise, COCB stimulation produces upward shift of dynamic range, which decreases with increasing noise level. At high noise levels, COCB-induced decompression of rate-level functions may occur with little or no dynamic range shift. This enables auditory nerve fibers to signal changes in tone level with changes in discharge rate at lower signal-to-noise ratios than would be possible otherwise. Broadband noise also produces upward shift of the dynamic range of single auditory nerve fiber BF tone response. Noise-induced dynamic range shift of BF tone response was measured as a function of noise level with and without COCB stimulation. COCB stimulation elevates the threshold of noise-induced dynamic range shift. This shift is thought to result from two-tone rate suppression. Increases in the threshold of noise-induced shift due to COCB stimulation therefore suggests an interaction between the mechanism of two-tone rate suppression and the mechanism by which COCB stimulation produces dynamic range shift. These interactions were further investigated by recording auditory nerve fiber rate responses to fixed-level BF excitor tones presented simultaneously with fixed-frequency variable level suppressor tones. Rate responses were recorded with and without COCB stimulation. Experimental results were quantified using a phenomenological model of two-tone rate suppression presented by Sachs and Abbas.

scholarly journals Threshold Tuning Curves of Chinchilla Auditory-Nerve Fibers. I. Dependence on Characteristic Frequency and Relation to the Magnitudes of Cochlear Vibrations

2008 ◽  
Vol 100 (5) ◽  
pp. 2889-2898 ◽  
Author(s):  
Andrei N. Temchin ◽  
Nola C. Rich ◽  
Mario A. Ruggero
Keyword(s):  
Auditory Nerve ◽  
Basilar Membrane ◽  
Frequency Tuning ◽  
Nerve Fibers ◽  
Lower Limbs ◽  
Gradual Transition ◽  
Characteristic Frequencies ◽  
Tuning Curves ◽  
Auditory Nerve Fibers ◽  
Threshold Tuning

Frequency-threshold tuning curves were recorded in thousands of auditory-nerve fibers (ANFs) in chinchilla. Synthetic tuning curves with 21 characteristic frequencies (187 Hz to 19.04 kHz, spaced every 1/3 octave) were constructed by averaging individual tuning curves within 2/3-octave frequency bands. Tuning curves undergo a gradual transition in symmetry at characteristic frequencies (CFs) of 1 kHz and an abrupt change in shape at CFs of 3–4 kHz. For CFs ≤3 kHz, the lower limbs of tuning curves have similar slopes, about −18 dB/octave, but the upper limbs have slopes that become increasingly steep with increasing frequency and CF. For CFs >4 kHz, tuning curves normalized to the CF are nearly identical and consist of three segments. A tip segment, within 30–40 dB of CF threshold, has lower- and upper-limb slopes of −60 and +120 dB/octave, respectively, and is flanked by a low-frequency (“tail”) segment, with shallow slope, and a terminal high-frequency segment with very steep slope (several hundreds of dB/octave). The tuning curves of fibers innervating basal cochlear sites closely resemble basilar-membrane tuning curves computed with low isovelocity criteria. At the apex of the chinchilla cochlea, frequency tuning is substantially sharper for ANFs than for available recordings of organ of Corti vibrations.

The Functional Role of Excitatory and Inhibitory Interactions in Chopper Cells of the Anteroventral Cochlear Nucleus

1994 ◽  
Vol 6 (6) ◽  
pp. 1127-1140 ◽  
Author(s):  
Ying-Cheng Lai ◽  
Raimond L. Winslow ◽  
Murray B. Sachs
Keyword(s):  
Cochlear Nucleus ◽  
Auditory Nerve ◽  
Dendritic Tree ◽  
Nerve Fibers ◽  
High Threshold ◽  
Spontaneous Rate ◽  
Anteroventral Cochlear Nucleus ◽  
Rate Versus ◽  
High Stimulus ◽  
Auditory Nerve Fibers

Chopper cells in the anteroventral cochlear nucleus of the cat maintain a robust rate-place representation of vowel spectra over a broad range of stimulus levels. This representation resembles that of low threshold, high spontaneous rate primary auditory nerve fibers at low stimulus levels, and that of high threshold, low spontaneous rate auditory-nerve fibers at high stimulus levels. This has led to the hypothesis that chopper cells in the anteroventral cochlear nucleus selectively process inputs from different spontaneous rate populations of primary auditory-nerve fibers at different stimulus levels. We present a computational model, making use of shunting inhibition, for how this level dependent processing may be performed within the chopper cell dendritic tree. We show that this model (1) implements level-dependent selective processing, (2) reproduces detailed features of real chopper cell post-stimulus-time histograms, and (3) reproduces nonmonotonic rate versus level functions in response to single tones measured.

scholarly journals Threshold Tuning Curves of Chinchilla Auditory Nerve Fibers. II. Dependence on Spontaneous Activity and Relation to Cochlear Nonlinearity

2008 ◽  
Vol 100 (5) ◽  
pp. 2899-2906 ◽  
Author(s):  
Andrei N. Temchin ◽  
Nola C. Rich ◽  
Mario A. Ruggero
Keyword(s):  
Spontaneous Activity ◽  
Auditory Nerve ◽  
Characteristic Frequency ◽  
Basilar Membrane ◽  
Frequency Tuning ◽  
Nerve Fibers ◽  
Nonmonotonic Dependence ◽  
Tuning Curves ◽  
Auditory Nerve Fibers ◽  
Threshold Tuning

Spontaneous activity and frequency threshold tuning curves were studied in thousands of auditory nerve fibers in chinchilla. The frequency distribution of spontaneous activity rates is strongly bimodal for auditory nerve fibers with characteristic frequency <3 kHz but only mildly bimodal for the entire sample. Spontaneous activity rates and thresholds at the characteristic frequency are inversely related. Auditory-nerve fibers with low spontaneous rate have tuning curves with lower tip-to-tail ratios and more sharply tuned tips than the tuning curves of fibers with high spontaneous rates. It is shown here that this dependence of tuning on spontaneous rates is consistent with a previously unnoticed nonmonotonic dependence on iso-velocity criterion of the frequency tuning of basilar membrane vibrations.

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