DEVELOPING ELECTROPHYSIOLOGICAL MEASURES OF BRAIN ACTIVITY TO OPTIMISE COCHLEAR IMPLANT OUTCOMES

For people with insufficient hearing to effectively use hearing aids, cochlear implants can provide great benefit, although they do not restore normal hearing. Cochlear implants stimulate the hearing nerve directly with electrical currents from a set of electrodes surgically implanted into the inner ear (cochlea). Although cochlear implants are a great success, a wide range in speech perception outcomes are observed.

The aim of this programme of research is to reduce the variability in performance as well as increasing the levels of speech recognition achieved by all. We propose to achieve this by using a special machine to measure brain activity in response to sound for cochlear implant users. This technique is used routinely in clinical practice and involves wearing a special hat to make the recordings. We will use this method to record responses at different parts of the hearing system between cochlea and brain. By understanding the relationship between these responses and speech understanding it will help us to appreciate the importance of different stages in the hearing pathway. These measures will allow us to observe the brain changes that take place once cochlear implants are switched on. We will define 'biomarkers' that can be used by clinicians to guide implant fitting and rehabilitation. A biomarker is an objective measurement of typical changes in the body.

We will develop guidance for adjusting the ways that sounds are sent through the cochlear implant or for switching off electrodes. For those with bilateral cochlear implants we will also develop guidelines for adjusting the implants to make the sounds more similar in each ear to improve the way that the ears work together. This research will be conducted with both adults and children to fully understand how people hear with a cochlear implant.

There are over 700,000 severe-to-profound hearing-impaired listeners with cochlear implants (CIs) worldwide and over 15,000 in the UK. CIs are life changing devices that restore hearing and give many individuals the opportunity to function in the hearing world. They provide a useable signal to the auditory system that enables young children to dramatically improve their developmental trajectory for speech and language acquisition. Despite being considered one of the most successful interventions in modern medicine, there is a huge amount of variation in CI hearing outcomes, in both child and adult CI users.

The aim of this research is to reduce variability in outcomes, and to improve performance to be closer to normal hearing even in highly performing individuals. To do so, we explore four man themes: variations in cortical responses to CI stimulation, how they relate to functional measures of hearing, and their shaping by ascending auditory inputs; brain adaptation and cross-modal reorganization following implant activation; evaluating if re-mapping based on cortical responses improves functional outcomes of hearing; and measuring neural indicators of binaural integration from bilateral implants.

We will employ electrophysiology techniques using electroencephalography (EEG) to objectively determine auditory capabilities of cochlear implant (CI) users and brain changes occurring following implant activation. Specific measures will look at electrode discrimination, within-channel modulation rate discrimination and between ear inter-aural time differences, inter-aural level differences. We will make use of responses to guide CI re-mapping. We will relate responses with psychophysical scores and speech perception data.

The findings will provide clinicians with tools to inform re-mapping and training interventions and, with the support of industry the implementation of important procedures, into clinical practice.

Who will benefit?
In the short term (over the first two years) the project will have a major impact on academic researchers investigating the structure and development of cochlear implant listening in children and adults. Even at this early stage, clinicians working with both children and adults using CIs will be aware of the emerging data and its significance. Clinicians will be invited to comment on the data in the context of child and adult CI provision. Over the mid-term of the project, there will be sufficient data for formal consultations with CI centres about the practicalities of the new electrophysiology techniques proposed, alongside initial thoughts on intervention programs that might benefit CI provision. At this stage, initial consultation with the manufacturers of the electrophysiological equipment used in the study will be made, with a view for slimming down the costs and complexity in order to be viable in NHS \ clinical settings. For a small group of CI users, some piloting of an Intervention program will have started: as such, these CI users will have been identified as needing attention and will have at least embarked on a program of intervention. During the final two years of the project, we expect feedback from other research organisations that have followed up and extended our initial findings. We expect further development of intervention programs based in clinics, and will invite comment from both CI clinicians and Speech and Language Therapists. Our intervention programs will have developed sufficiently to consult with the manufacturers of CIs. We expect that changes to the provision of the clinical software supplied to CI centres can be made. The end-product of this research effort are the CI users themselves, both adult and children, and the benefit is expected to be greatest in those with the poorest speech perception abilities.

How will they benefit?
Academic researchers will keenly anticipate the outcomes of the research as it provides much missing information about the cortical organisation of auditory information post CI activation. While some knowledge has been gained from behavioural measures in adult CI implantees, tools for exploring objective measures of cortical organisation are absent. These same tools can be used for exploring child auditory maturation post CI activation. While CI clinicians are often able to perform behavioural speech tests of CI performance, they will benefit enormously from the electrophysiological tools provided by the project for measuring objective speech performance. The commercial interests: cochlear implant companies (e.g. Advanced Bionics, Cochlear Corp., MedEl) and electrophysiology equipment companies (e.g. BioSemi)) will be interested in refining their products in light of the study outcomes. Finally, assuming our intervention programs are at least partially successful, child and adult CI users (together with related carer's of CI users, including parents and teachers) will benefit from better speech performance, compared to their performance before the project.