Noninvasive Chronic Recording of Auditory Nerve Potentials

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Abstract
A system is described which allows repeated, noninvasive recording of auditory nerve responses in the cat to transient acoustic stimuli using a closed acoustic system. N1 responses to clicks are recorded from a stainless steel ring electrode at the end of a hollow earbar, the tapered end of which is made of insulating plastic. Acoustic stimuli are generated by a dynamic earphone coupled to the earbar. A calibrated probe microphone is also incorporated into the earbar to measure sound pressure near the tympanic membrane. This allows better stimulus control than is available with tree-field systems. To facilitate insertion of the earbar, meatoplasties were performed on all animals. Responses recorded with this system in anesthetized cats are described and compared with those recorded at the round window. Good repeatability of measurements is described for an animal population of 20 domestic cats over a period of several months. For some of these animals, response amplitude varied from one session to another, but response latency, especially for condensation clicks, was consistent. By comparing statistics of multiple measurement of both N1 amplitude and latency for rarefaction and condensation clicks, it is concluded that the N1 latency vs click-level function for condensation clicks provides the most reliable measure of the cat's auditory nerve function.

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