Journal of Otology & RhinologyISSN: 2324-8785

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Research Article, J Otol Rhinol Vol: 5 Issue: 5

Epidural Recordings of Auditory Evoked Potentials in Cochlear Implant Users: First Experiences

Haumann S1,3*, Bauernfeind G1,3, Bleichner MG2,3, Teschner MJ1,3, Debener SD2,3 and Lenarz T1,3
1ENT Department, Hannover Medical School, Germany
2Neuropsychology, Carl-von-Ossietzky-University of Oldenburg, Germany
3Cluster of Excellence, Hearing4All, Germany
Corresponding author : Haumann S
ENT Department, Hannover Medical School, Carl-Neuberg-Str. 1, 30625 Hannover, Germany
Tel:
++49-511-532-6635
E-mail:
[email protected]
Received: July 01, 2016 Accepted: July 20, 2016 Published: July 20, 2016
Citation: Haumann S, Bauernfeind G, Bleichner MG, Teschner MJ, Debener SD, et al. (2016) Epidural Recordings of Auditory Evoked Potentials in Cochlear Implant Users: First Experiences. J Otol Rhinol 5:5. doi:10.4172/2324-8785.1000292

Abstract

On the long term it is desirable for cochlear implant (CI) users to control their device via brain signals. For an everyday life application it is convenient to use implanted electrodes for recording the signals. In this pilot project we investigate in a first step the feasibility of implanting epidural electrodes temporally and the possibility to record auditory evoked potentials (AEPs) in the course of several days. First recordings in three patients show promising results. Altogether the approach is feasible, safe and well tolerated by the patients, and the AEP waves can be clearly seen.

Keywords: Epidural recordings; Cochlear implant; Auditory evoked potentials

Keywords

Epidural recordings; Cochlear implant; Auditory evoked potentials

Introduction

On the long term it is desirable for cochlear implant (CI) users to control their device using brain signals (brain-computer-interface, BCI). This technology provides the user with an artificial output channel that utilizes the information from neuronal activity of the brain and which does not rely on the normal output pathways of peripheral nerves and muscles. Typically, a BCI detects voluntary changes in electroencephalography (EEG) signals and translates different brain states into appropriate commands for communication and control [1]. BCIs could provide active and passive control over the hearing devices. Active control could entail to select the preferred listening program, without the need of a remote control. Additionally, beside this active use of BCI control, such systems can also work in a passive way [2]. Passive control could entail automatic adjustments of a CI in response to the user’s cognitive state (for example reflecting listening effort, or loudness experience).
A promising approach, when considering the application of BCI systems for the control of a CI, is the use of auditory evoked potentials (AEP), including the P300 wave. Previous studies have shown the possible suitability of auditory paradigms [3-5]. However, all these investigations are based on non-invasive signal acquisition which requires the use of additional EEG electrodes mounted on the users scalp which are clearly visible, uncomfortable and less robust to artifacts in everyday situations [6]. Using signals recorded from the surface of the brain [7] produces better results, but this invasiveness limits the acceptance for most BCI applications.
However, for a CI controlled by neural activity in everyday life implantable electrode are convenient. Especially if the electrodes are integrated into the CI (which needs to be implanted anyway) the use of invasively recorded signals is a promising approach.
For feasibility studies electrodes have to be used which are implanted temporally. First invasive recordings within CI surgeries were already done in the early years of cochlear implants [8]. Here for example electrically evoked auditory brainstem responses (eABR) were recorded in order to determine the best stimulation site using different stimulation electrodes and sites. Similar experiments were done by directly stimulating the auditory nerve within suitable surgeries [9]. These and other intraoperative studies gave deep insights into the mechanisms of stimulating the auditory cortex (AC) and therewith lead to large developments in the field of CI and auditory brainstem implants (ABI).
However, under the influence of anesthesia only auditory brainstem responses (ABR) can be recorded reliably. Thus, these intraoperative studies were limited to the recording of ABR, whereas for cognitive control of the CI cortical potentials are needed. These potentials can only be recorded reliably when the patient is awake. Therefore, we looked for electrodes that can be implanted within the surgery, lead outside of the skin, remain for a couple of days during which cortical potentials are recorded, and then be removed without re-opening the operation wound.

Materials and Methods

In this pilot project we study the possibilities of recording neuronal signals via epidural electrodes in CI users. For this purpose three epidural electrodes (AD-Tech Medical Instrument Corporation, Racine, WI, USA) are implanted temporarily during the CI surgery. With these electrodes AEP recordings are performed and compared to standard clinical electrodes settings. The recordings are done intraoperatively and postoperatively during the first days of CI use. For the course of the measurements the patient is staying on the ward and closely watched by the ward physician. Having completed the measurements after 4-5 days the epidural electrodes are removed. After that the patient is watched for one or two more days and then sent home.
During the surgery eABR are recorded. The stimulation is done via the CI by using the clinical standard steering setup from the CI manufacturer. For recording the Nicolet Viking EDX is used (Natus Medical Incorporated, Pleasanton, CA, USA). The recorded data is compared to our clinical standard setup using subdermal needle electrodes (Medtronic, Minneapolis, MI, USA). The recording is done on five channels simultaneously with the three epidural electrodes, one needle electrode at the ipsilateral and one at the contralateral earlobe. The reference for all channels was a needle electrode at the vertex, and the ground electrode was a needle electrode at the forehead.
In the days after the surgery different AEPs are recorded: ABR, middle latency responses (MLR), cortically evoked response audiometry (CERA), mismatch negativity (MMN) and P300. For the measurements the CI is stimulated acoustically with a 1 m sound tube using clicks and tone bursts. For the recording the Nicolet Synergy EDX is used (Natus Medical Incorporated, Pleasanton, CA, USA). The recorded data is compared to our clinical standard setup using adhesive electrodes (Asmuth GmbH Medizintechnik, Minden, Germany). The recording is done on five channels simultaneously with the three epidural electrodes, one adhesive electrode at the ipsilateral and one at the contralateral mastoid. The reference for all channels was an adhesive electrode at the vertex, and the ground electrode was an adhesive electrode at the forehead.
For this project adult patients are recruited who are scheduled for a CI implantation in our clinic. The patients are postlingually deafened. Also different CI brands are used. So far three patients participated in the study. Exemplarily some of the data obtained from the second patient is shown here. This patient was male, 48 years old,and was provided on the right side with a HiRes90k Advantage HiFocus V (MidScala) implant and a Naida CI Q90 processor (Advanced Bionics, Valencia, CA, USA). The epidural electrodes are shown in Figure 1.
Figure 1: Placing of the three epidural electrodes: cranial anterior, cranial medial and cranial posterior. Here the electrodes are prepared for remaining for a couple of days and the leads are directed outside.

Results

Our results showed the principal feasibility of this approach. The epidural electrodes could be placed and fixed such that they didn’t move within the course of the measurements. After 4-5 days they could be removed safely. In all three cases there was no pain for the patient during the removal.
In the intraoperative recordings the results of the eABR were comparable between the recording electrodes, but with the epidural electrodes the potentials were clearer than with the subdermal needle electrodes.
Postoperatively again we detected a better signal quality and clearer potentials with the epidural settings. Exemplarily the data of the CI stimulated CERA is shown in this work. The recorded potentials are shown in Figure 2. The N1 was much clearer than with the adhesive electrodes and also visible at lower stimulation intensities. Also the signal was less disturbed by artefacts. Also differences between the electrode positions of the epidural electrodes could be detected.
Figure 2: Simultaneous recordings of cortically evoked response audiometry (CERA). Left panel: To the right the five recording electrodes are presented: right and left mastoid are recorded with adhesive electrodes; anterior, medial and posterior are the three epidural electrodes. The reference is placed at the left forehead, and the ground at the middle forehead (both were adhesive electrodes). Downwards three loudness levels are presented. Right panel: All five channels are plotted overlying for the highest stimulation level.

Conclusion

Altogether the approach is feasible, safe and well tolerated by the patients. First epidural recordings show promising results with clear evoked potentials. Thus, more data can be obtained by doing the measurements with more patients. Also, further steps towards the use of brain signals for device control can be performed, for example an offline classification of the signals and therewith the simulation of a BCI system.

Funding

This work is supported by the Cluster of Excellence “Hearing4all” (EXC 1077/1).
Author’s Statement
Conflict of interest: Authors state no conflict of interest.
Material and methods: Informed consent: Informed consent has been obtained from all individuals included in this study.
Ethical approval: The research related to human use has been complied with all the relevant national regulations, institutional policies and in accordance the tenets of the Helsinki Declaration, and has been approved by the authors’ institutional review board or equivalent committee.

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