Can event-related potentials be evoked by extra-cochlear stimulation and used for selection purposes in cochlear implantation?

To investigate whether electrically evoked event-related responses (P300) could be elicited by extra-cochlear stimulation, measurements were performed on a group of adults fitted with the single-channel extra-cochlear implant. To optimize measurement conditions, and because of the low number of subjects still using an extra-cochlear device in our cochlear implant programme, measurements were also performed on a group of experienced users fitted with the intra-cochlear Nucleus multichannel device. For reference purposes, subjects with normal hearing (control group) were also included in the study. Reproducible late latency responses (N1 and P2 peaks) were found in the five extra-cochlear implant users, while P300s were present in four out of these five subjects. The latencies were longer than those of the control group, but were similar to those obtained in the intra-cochlear implant group. Significant correlations were found for most N1, P2 and P300 measurements evoked by the tonal stimuli and by speech stimuli. The P300 amplitudes, evoked by either tonal or speech stimuli, appeared to be related to speech perception ability. This led to the conclusion that N1, P2 and P300 measurements may have potential as a clinical tool for preoperative prediction and postoperative evaluation of sound processing on a cortical level.

The influence of the concentration of volatile anesthetics on the stapedius reflex determined intraoperatively during cochlear implantation in children

OBJECTIVE

The goal of this study was, first, to determine the effect of the concentrations of volatile anesthetics (halothane and isoflurane) on the intraoperative elicited electrical stapedius reflex threshold (ESRT) and, second, to evaluate the relation between the ESRTs and postoperative C-levels.

STUDY DESIGN

This was a prospective clinical study in a single subject design.

SETTING

The study was conducted at University Hospital Nijmegen, which is a tertiary care and cochlear implant center in The Netherlands.

PATIENTS

The study population comprised 13 deaf children (6 males and 7 females) undergoing cochlear implantation.

RESULTS

In most of the children, increasing the concentration of volatile anesthetic agent resulted in higher stapedius reflex threshold. After correction for this effect, a good relation was found between ESRT and C-level in all children, except for one.

CONCLUSIONS

The outcome of this study supports the determination of intraoperative ESRTs for programming of the speech processor postsurgery.

Intra- and interindividual correlations between auditory evoked potentials and speech perception in cochlear implant users

Several electrophysiological techniques have been used to supplement behavioural measurements in the evaluation of the benefit of cochlear implantation, namely the electrically evoked auditory brainstem response (EABR), electrically evoked middle latency response (EMLR) and electrically evoked late latency response (EALR). To study the interdependence of these responses, the present paper deals with a combination of EABR, EMLR and EALR measurements obtained from 15 postlingually deaf subjects implanted with the Nucleus multichannel device at the University Hospital Nijmegen. In particular, we investigated whether there were intercorrelations between amplitude and latencies of the evoked potential peaks and/or correlations with long-term speech perception scores. Significant correlations were found between the peak V amplitude of the EABR and the NaPa and NbPb amplitudes of the EMLR. No significant correlation was found between the EABR and EMLR amplitudes on the one hand and EALR peak amplitudes on the other. In addition, no significant correlations were found between any of the EABR or EMLR peak amplitudes and speech perception test results. A moderate but significant relation was found between the EALR peak amplitude and speech perception test results. Unlike latencies of earlier peaks, the latency of the EALR peak P2 was significantly related to the speech perception scores.

Cochlear implantation: a review of the literature and the Nijmegen results

The field of cochlear implantation is developing rapidly. In subjects with bilateral profound deafness who gain no benefit from conventional hearing aids the aim of cochlear implantation is to provide a means for them to receive auditory sensations. Throughout the world, most cochlear implant centres are still continuing their research efforts to improve the results with this technique. Although it is still difficult to predict how an individual will perform with a cochlear implant, the success of cochlear implantation can no longer be denied. In this paper, we review some recent papers and reports, and the results of the various Nijmegen cochlear implant studies. Data about subject selection, examinations, surgery and the outcome are discussed. Our results were in good agreement with those of other authors. It can be concluded once again that cochlear implantation is an effective treatment for postlingually deaf adults and children, and for prelingually (congenital or acquired) deaf children with profound bilateral sensorineural deafness.

Cochlear implantation in deaf children

A cochlear implant (CI) is a hearing device introduced in the 1980s for profoundly deaf subjects who gained little or no benefit from powerful hearing aids. This device comprises an electrode array inserted in the cochlea, connected to an internal receiver, and an externally worn speech processor. The CI transforms acoustic signals into electrical currents which directly stimulate the auditory nerve. Since the early 1990s, cochlear implantation in children has been developing rapidly. Although it is still difficult to predict how a child will perform with a cochlear implant, the success of cochlear implantation can no longer be denied. In this paper, some recent papers and reports, and the results of the various Nijmegen cochlear implant studies, are reviewed. Issues about selection, examinations, surgery and the outcome are discussed. Overall, our results were comparable with those of other authors. It can be concluded that cochlear implantation is an effective treatment for postlingually deaf as well as prelingually (congenital or acquired) deaf children with profound bilateral sensorineural deafness.

The relation between age at the time of cochlear implantation and long-term speech perception abilities in congenitally deaf subjects

The issue of whether an upper age limit should be set for cochlear implantation in congenitally deaf subjects has often been debated. To gain more insight, the speech perception abilities were analyzed of 12 congenitally deaf subjects whose age at the time of cochlear implantation ranged from 4 to 33 years. Subjects implanted during adulthood only showed progress during the first few months after the speech processor had been fitted and their long-term results were poor compared to those of children implanted early in life. This latter group showed steady improvement over the whole evaluation period. The present results support the notion that the earlier in life implantation is performed, the better the development of speech perception. Based on the progress-over-time profiles and data on actual daily use of the cochlear implant, it can be suggested that implantation of congenitally deaf subjects during or after puberty offers only limited benefit.