| Objective:1 Compared to normal auditory system,cochlear implant can not provide enough information,especially tonal information,so tonal discrimination is not so good in cochlear implant recipients.ERP can offer processing information to acoustic stimulation in cerebral cortex, MMN is an event related potentials of preattentive processing to stimulation signal,is Cerebullar processing of stimulation before attention,is a course of automatic detection and processing. Using mismatch negativity(MMN) of event related potentials(ERPs) as an index in our experiment,compared differences of pre-attentive auditory processing of Chinese tones between prelingual cochlear implant(CI) recipients and matched controls.At the same time,we compared the functions of two kinds of MMN.2 tested the threshold for cochlear implant electrodes stimulating the facial nerve,and investigate the change and the regularity of the change.3 To report and discuss the use of promontory stimulation test in cochlear implant candidates with poor response to acoustic stimulation test.Methods:1 cochlear implant recipients are those who were operated at Department of Otolaryngology and Head Neck Surgery of Peking Union Medical College Hospital.Auditory materials included four Chinese tones and a pure tone,we used 25 group of Chinese character as these,100 Chinese characters totally,made up four stimulation blocks,a control block and three oddball blocks.event related potentials were recorded and analyzed by a NeuroScan SynAmps EEG amplifier and Acquire software Scan4.3.Oddball MMNs and control MMNs of CI users and normal subjects were obtained by different subtracting,there were two kinds of MMNs obtained in cochlear implant recipients and normal subjects,oddball MMN and control MMN.2 Used the neural response telemetry(NRT) equipment of cochlear implant and facial nerve monitor to record the threshod for the response of facial nerve to different intensive electric stimulation.Through analysis,try to find the changing regularity according to different intensive electric stimulation.3 Selected twelve recipients of cochlear implant performed and mapped in PUMCH from 1995 to 2007,who adopted promontory stimulation test.We summarized the postoperative results of these cochlear implant recipients who performed poorly in acoustic stimulation and were operated under the direction of promontory stimulation test,and discussed the role of promontory stimulation test in cochlear implantation.Result:1 Obvious MMNs could be obtained from Cochlear implant recipients and normal subjects.Oddball MMN:oddball MMNs of normal person and cochlear implant recipients all had two negative waves,Latency of the first wave of oddball MMN was shorter in Cochlear implant recipients than in normal subjects,latency of the second wave was also shorter in Cochlear implant recipients than normal subjects,but the difference was not as significant as the first wave. Control MMN:in control paradigm,the first negative wave disappeared in normal subjects;In control MMNs of cochlear implant recipients,changes of the first wave are not as significant as normal subjects.In normal subjects,there were significant differences for the amplitudes of control MMN(corresponding to the second wave) about three Chinese tones block,but there were no difference in cochlear implant recipients.2 through increasing or decreasing the intension of electric stimuli,the threshold of facial nerve for electric stimuli could be obtained from all electrodes of all cochlear implant recipients,there were three kinds of variation trends of threshold:(1) Decreasing type.(2) Decreasing in anterior segment,stable in posterior segment, there is a obvious knee point.(3) Decreasing in anterior segment,stable in posterior segment, there is a obvious knee point too,but fluctuating in whole range.3 According to the results of promontory stimulation test,patients who had poorly acoustic stimulation tests were performed of cochlear implantion successfully;intraoperation and postoperation NRT test could be proceeded well;postoperative speech perception tests were satisfying.Conclusion:1 There were evident MMN in processing different Chinese tones in CI users and normal person,this indicated that CI users and normal person both can process Chinese tones in preattentive period.But from the waveforms of grand average and the results of statistical analysis, we could find the waveforms of CI users are irregular,and there were not significant differences in processing different Chinese tones in statistical analysis.Compared to normal person,the processing of CI users was more difficult than that of normal person,and the ability of processing in CI users was decreased.In normal subjects,compared to oddball MMN,control MMN eliminated the effect of acoustic physical characteristics,could reflect the real memory-based pre-attentive processing,it could reflect the differences in processing different Chinese tones.In experiments of preattentive process for Chinese tones,control paradigm is more sensitive than oddball paradigm,is more objective in evaluating the function of preattentive process,because it avoids the misestimation of the MMN as oddball paradigm,we believe control MMN is more valuable in practice.2 From the end to the tip of cochlear implant electrodes,there is decreasing trend of the facial nerve response thresholds to electric stimulation,but the decreasing styles are different.This can indicated that tip electrodes are closer to facial nerve,and the courses of straight electrodes in cochlear ducts are more irregular.3 cochlear implant candidates with poor response to acoustic stimulation test can get benefit from promontory stimulation test.
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