Laser stimulation of single auditory nerve fibers.
OBJECTIVE
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.


METHODS
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.
Littlefield
Philip D
PD
Department of Surgery, ENT Section, Walter Reed Army Medical Center, Washington, DC 20307-5001, USA.
Vujanovic
Irena
I
Mundi
Jagmeet
J
Matic
Agnella Izzo
AI
Richter
Claus-Peter
CP
D000161:Acoustic Stimulation; D000200:Action Potentials / Q000502:physiology; D000818:Animals; D003054:Cochlear Implants; D003056:Cochlear Nerve / Q000166:cytology / Q000502:physiology*; D005849:Gerbillinae; D054023:Lasers, Semiconductor; D009412:Nerve Fibers / Q000502:physiology*