Shapes of Tuning Curves for Single Auditory‐Nerve Fibers

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.

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

Journal of Neurophysiology ◽

10.1152/jn.90639.2008 ◽

2008 ◽

Vol 100 (5) ◽

pp. 2899-2906 ◽

Cited By ~ 26

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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Acoustic reflex frequency selectivity in single stapedius motoneurons of the cat

Journal of Neurophysiology ◽

10.1152/jn.1992.68.3.807 ◽

1992 ◽

Vol 68 (3) ◽

pp. 807-817 ◽

Cited By ~ 29

Author(s):

J. B. Kobler ◽

J. J. Guinan ◽

S. R. Vacher ◽

B. E. Norris

Keyword(s):

Auditory Nerve ◽

High Frequency ◽

Low Frequency ◽

Nerve Fibers ◽

Main Function ◽

Acoustic Reflex ◽

Tuning Curves ◽

Acoustic Reflexes ◽

Auditory Nerve Fibers ◽

Decerebrate Cats

1. The sound frequency selectivities of single stapedius motoneurons were investigated in ketamine anesthetized and in decerebrate cats by recording from axons in the small nerve fascicles entering the stapedius muscle. 2. Stapedius motoneuron tuning curves (TCs) were very broad, similar to the tuning of the overall acoustic reflexes as determined by electromyographic recordings. The lowest thresholds were usually for sound frequencies between 1 and 2 kHz, although many TCs also had a second sensitive region in the 6- to 12-kHz range. The broad tuning of stapedius motoneurons implies that inputs derived from different cochlear frequency regions (which are narrowly tuned) must converge at a point central to the stapedius motoneuron outputs, possibly at the motoneuron somata. 3. There were only small differences in tuning among the four previously described groups of stapedius motoneurons categorized by sensitivity to ipsilateral and contralateral sound. The gradation in high-frequency versus low-frequency sensitivity across motoneurons suggests there are not distinct subgroups of stapedius motoneurons, based on their TCs. 4. The thresholds and shapes of stapedius motoneuron TCs support the hypothesis that the stapedius acoustic reflex is triggered by summed activity of low-spontaneous-rate auditory nerve fibers with both low and high characteristic frequencies (CFs). Excitation of high-CF auditory nerve fibers by sound in their TC “tails” is probably an important factor in eliciting the reflex. 5. In general, the most sensitive frequency for stapedius motoneurons is higher than the frequency at which stapedius contractions produce the greatest attenuation of middle ear transmission. We argue that this is true because the main function of the stapedius acoustic reflex is to reduce the masking of responses to high-frequency sounds produced by low-frequency sounds.

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