Abstract
The present study was designed to improve the method of the chronic measurement of cochlear nerve compound action potentials (CAP) reported by Hildesheimer et al (1979). After removing the facial nerve, a silver/silver-chloride wire was inserted into the facial canal approximately 6mm from the stylomastoid foramen so as to reach the second gene of the canal. The electrode was insulated with teflon except the cut end which was coated with silver chloride. Dental cement was used to fix the electrode to the mastoid bone. A sufficiently large CAP (50-120μV at 80 dBSPL) was evoked with this method and 4μV CAP was obtained at the sound stimulation of the CAP threshold (10μV with the round window recording). Although the CAP threshold was unstable within the first one week after the implantation of the electrode, the values were consistent and reproducible thereafter. This method does not require any difficult procedure and the success rate is very high. It is our conclusion that this method is quite suitable for the long term observation of the cochlear potentials.
