ELECTROPHYSIOLOGICAL FINDINGS IN TWO BILATERAL COCHLEAR IMPLANT CASES: DOES THE DURATION OF DEAFNESS AFFECT ELECTRICALLY EVOKED AUDITORY BRAIN STEM RESPONSES?

Bilateral cochlear implantation providesan interesting model for in vivo studyof the effectof long-term profound deafness on neural transmission. Wepresentelectrophysiological observations on 2 patients implanted with the MXM Binaural Digisonic Con-vexsystem. This uncommon designconsistsof 2 electrodearraysplacedbilaterally into the scala tympani and controlled by a single speechprocessor. In both patients, the durationof deafnessbeforecochlear implantation clearly differedfrom one ear to the other. Electrically evoked auditory brain stem responses (EABRs) were measured and the EABRsfrom the ear with the longerdeafness duration showed a lengthening of waveVlatency. In I patient,recordings fromthis ear alsoshoweda lackof reproducibility of wave III. The data suggest that neural responsiveness in the peripheral and intermediate auditorypathways is adversely affected by deaf-nessduration. PoorEABRs on oneear possiblyresultfromthe totalduration of deafnessin thisear and/orcompensation by theother ear