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Laser stimulation of single auditory nerve fibers§

Authors

  • Philip D. Littlefield MD,

    Corresponding author
    1. Department of Surgery, ENT Section, Walter Reed Army Medical Center, Washington, DC
    2. Department of Otolaryngology, Feinberg Medical School, Northwestern University, Chicago, Illinois
    • ENT Section, Department of Surgery (Building 2), Walter Reed Army Medical Center, 6900 Georgia Ave NW, Washington, DC 20307-5001
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  • Irena Vujanovic PhD,

    1. Department of Otolaryngology, Feinberg Medical School, Northwestern University, Chicago, Illinois
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  • Jagmeet Mundi MD,

    1. Department of Otolaryngology, Feinberg Medical School, Northwestern University, Chicago, Illinois
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  • Agnella Izzo Matic PhD,

    1. Department of Otolaryngology, Feinberg Medical School, Northwestern University, Chicago, Illinois
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  • Claus-Peter Richter MD, PhD

    1. Department of Otolaryngology, Feinberg Medical School, Northwestern University, Chicago, Illinois
    2. Department of Biomedical Engineering, The Hugh Knowles Center, Northwestern University, Evanston, Illinois, U.S.A.
    3. Department of Communication Sciences and Disorders, The Hugh Knowles Center, Northwestern University, Evanston, Illinois, U.S.A.
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    • C.-P.R. and A.I.M. have patents using laser stimulation technology and are partially funded by Lockheed Martin Aculight.


  • This project has been funded in whole or in part with federal funds from the National Institute on Deafness and Other Communication Disorders, National Institutes of Health, Department of Health and Human Services, under Contract No. HHSN260-2006-00006-C/NIH No. N01-DC-6-0006, by NIH Grants R41 DC008515-01 and F31 DC008246-01, and the Capita Foundation.

  • §

    The views expressed in this presentation are those of the authors and do not reflect the official policy of the Department of Army, Department of Defense, or U.S. Government.

  • All experiments were performed at Northwestern University.

  • This work is a Triological Society Candidate Thesis and won the Edmund Prince Fowler Award.

Abstract

Objectives/Hypothesis:

One limitation with cochlear implants is the difficulty stimulating spatially discrete spiral ganglion cell groups because of electrode interactions. Multipolar electrodes have improved on this some, but also at the cost of much higher device power consumption. Recently, it has been shown that spatially selective stimulation of the auditory nerve is possible with a mid-infrared laser aimed at the spiral ganglion via the round window. However, these neurons must be driven at adequate rates for optical radiation to be useful in cochlear implants. We herein use single-fiber recordings to characterize the responses of auditory neurons to optical radiation.

Study Design:

In vivo study using normal-hearing adult gerbils.

Methods:

Two diode lasers were used for stimulation of the auditory nerve. They operated between 1.844 μm and 1.873 μm, with pulse durations of 35 μs to 1,000 μs, and at repetition rates up to 1,000 pulses per second (pps). The laser outputs were coupled to a 200-μm-diameter optical fiber placed against the round window membrane and oriented toward the spiral ganglion. The auditory nerve was exposed through a craniotomy, and recordings were taken from single fibers during acoustic and laser stimulation.

Results:

Action potentials occurred 2.5 ms to 4.0 ms after the laser pulse. The latency jitter was up to 3 ms. Maximum rates of discharge averaged 97 ± 52.5 action potentials per second. The neurons did not strictly respond to the laser at stimulation rates over 100 pps.

Conclusions:

Auditory neurons can be stimulated by a laser beam passing through the round window membrane and driven at rates sufficient for useful auditory information. Optical stimulation and electrical stimulation have different characteristics; which could be selectively exploited in future cochlear implants. Laryngoscope, 2010

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