[Experimental study of extracochlear electric stimulation]

The efficiency and feasibility of chronic extracochlear implantation and electric stimulation were studied in two adult cats and four 2-month kittens. The first electrode was placed on the round window by fixing the lead wire on the bridge of aditus between the middle ear and bulla cavity; the second electrode was placed on the surface of the tympanic promontory; the third was inserted into the temporal muscle out of the bulla and the forth fixed in transverse sinus with dental cement. ABRs and EABRs were recorded pre- and postoperatively and during electric stimulation. The results indicated that: (1) The chronic electric stimulation could be carried on with round window electrode; the fixation of round window electrode is satisfactory without the influence of postnatal skull growth. (2) EABRs evoked by electrically stimulating round window electrode were mainly generated by the auditory system, but its short response was partly generated by the vestibular system. (3) EABRs evoked by electric stimulation of round window electrode were contaminated by facial nerve response which could be inhibited by 2% xylocaine injection of foramen stylomastoid. (4) The EABRs evoked by stimulating tympanic promontory electrode is uncertain.