EEG-based diagnostics of the auditory system using cochlear implant electrodes as sensors

Abstract

The cochlear implant is one of the most successful medical prostheses, allowing deaf and severely hearing-impaired persons to hear again by electrically stimulating the auditory nerve. A trained audiologist adjusts the stimulation settings for good speech understanding, known as “fitting” the implant. This process is based on subjective feedback from the user, making it time-consuming and challenging, especially in paediatric or communication-impaired populations. Furthermore, fittings only happen during infrequent sessions at a clinic, and therefore cannot take into account variable factors that affect the user’s hearing, such as physiological changes and different listening environments. Objective audiometry, in which brain responses evoked by auditory stimulation are collected and analysed, removes the need for active patient participation. However, recording of brain responses still requires expensive equipment that is cumbersome to use. An elegant solution is to record the neural signals using the implant itself. We demonstrate for the first time the recording of continuous electroencephalographic (EEG) signals from the implanted intracochlear electrode array in human subjects, using auditory evoked potentials originating from different brain regions. This was done using a temporary recording set-up with a percutaneous connector used for research purposes. Furthermore, we show that the response morphologies and amplitudes depend crucially on the recording electrode configuration. The integration of an EEG system into cochlear implants paves the way towards chronic neuro-monitoring of hearing-impaired patients in their everyday environment, and neuro-steered hearing prostheses, which can autonomously adjust their output based on neural feedback.

Towards Decoding Selective Attention Through Cochlear Implant Electrodes as Sensors in Subjects with Contralateral Acoustic Hearing

“…They were also able to record CAEPs using only CI electrodes, even though the morphology was less clear and peaks were not detectable in all subjects. The CAEPs recorded in the present study show very similar morphologies to the CAEPs presented in the studies of McLaughlin et al (2012) and Somers et al (2021). However, the present experimental setup was not restricted by extensive measurement time and it was based on a clinical transcutaneous implant without requiring an additional external amplifier.…”

“…The disadvantage of the approach of McLaughlin et al (2012) was that they required the concatenation of the time-shifted windows causing extensive measurement time to record CAEPs. Somers et al (2021) performed continuous EEG recording via a CI from the company Cochlear Ltd. using a percutaneous connector and a high-quality external amplifier. They tested different electrode configurations and found that the best configuration was a hybrid recording in which the Cz scalp electrode was referenced to an intracochlear electrode.…”

“…A limitation of all studies is the small sample size. McLaughlin et al (2012) and Somers et al (2021) each included 3 subjects and the present study included 5 subjects. Further studies with more subjects are required in order to increase the robustness of the results to draw more general conclusions about the optimal electrode configuration.…”

“…This procedure was highly time consuming and thus is not practically applicable in clinical routine measurements. Somers et al (2021) performed continuous EEG recording via a CI from the company Cochlear Ltd. using a percutaneous connector. Moreover, a highquality external amplifier could be used and the invasive CI electrodes could be combined with non-invasive scalp channels for a hybrid EEG recording.…”

“…Moreover, a highquality external amplifier could be used and the invasive CI electrodes could be combined with non-invasive scalp channels for a hybrid EEG recording. However, Somers et al (2021) approach also lacks the practical applicability because it requires an invasive procedure which goes in hand with an increase of multiple risks for the patient, such as infection. Nevertheless, both approaches prove the general feasibility of CI-based recording of cortical signals such as CAEPs and motivate the development of fully implantable CI-based EEG (iEEG).…”