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Parallel pathways at the auditory periphery

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We should consider the possibility that Low- and High- spontaneous rate (SR) auditory nerve fibers (ANFs) [1] constitute two different parallel pathways at the auditory periphery. The present study used a computational model of the auditory periphery [2] to demonstrate that Low- and High- SR ANFs have contrasting response properties. Anatomical studies suggest that Low- and High- SR ANF types have separate innervation sites (Figure 1A) on the same inner hair cell; lower-SR fibers synapse on the modiolar side and high-SR fibers synapse on the pillar side [3]. My hypothesis, prior to modeling the tuning curves (Figure 1B), was that Low Spontaneous Rate (Low-SR) fibers have a higher threshold for simulation and thus will have demonstrably sharper frequency selectivity than High-SR fibers. The results of the simulation support this framework; Low-SR ANFs were shown to have sharper frequency tuning (Figure 1B) than High-SR ANFs throughout a range of characteristic frequencies (CFs). While Low-SR ANFs have sharper frequency selectivity (Figure 1B), High-SR ANFs have finer temporal resolution, as the rate of change of the mean firing rate in High-SR ANFs was well above that of Low-SR fibers in the simulation (Figure 1C). It would seem that Low-SR and Medium-SR fibers (i.e. Lower-SR fibers) are optimized for “place theory” frequency coding and High-SR fibers are optimized for “volley-theory” synchronous phase locking. Future modeling efforts might maintain the integrity of these two parallel pathways, optimized for fine spectral (Lower-SR) and fine temporal (High-SR) resolution, by separating rather than summing their respective outputs.

Figure 1
figure1

Innervation sites (A), tuning curves (B) and temporal response properties for Low- and High- SR ANFs

References

  1. 1.

    Liberman MC: Auditory-nerve response from cats raised in a low-noise chamber. J Acoust Soc Am. 1978, 63 (2): 442-455. 10.1121/1.381736.

  2. 2.

    Zilany MSA, Bruce IC, Carney LH: Updated parameters and expanded simulation options for a model of the auditory periphery. J Acoust Soc Am. 2014, 135: 283-286. 10.1121/1.4837815.

  3. 3.

    Bharadwaj HM, Verhulst S, Shaheen L, Liberman M, Shinn-Cunningham BG: Cochlear neuropathy and the coding of supra-threshold sound. Front Syst Neurosci. 2014, 8 (26): 10.3389/fnsys.2014.00026.

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Correspondence to Marcos A Cantu.

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Keywords

  • Hair Cell
  • Tuning Curve
  • Parallel Pathway
  • Auditory Nerve Fiber
  • Spontaneous Rate