Assessing Functional Connectivity in Paediatric Bilateral Cochlear Implant Users

Smieja, Daniel 1, 2 ; Dunkley, Benjamin 4, 5, 6 ; Papsin, Blake 1, 3 ; Gordon, Karen 1, 3, 7

1. Archie’s Cochlear Implant Laboratory, The Hospital for Sick Children, Toronto, Canada; 2. Institute of Biomaterials and Biomedical Engineering, University of Toronto, Canada; 3. Department of Otolaryngology-Head and Neck Surgery, University of Toronto, Canada; 4. Department of Diagnostic Imaging, The Hospital for Sick Children, Toronto, Canada; 5. Neuroscience & Mental Health Program, The Hospital for Sick Children Research Institute, Toronto, Canada; 6. Department of Medical Imaging, University of Toronto, Toronto, Canada; 7. Institute of Medical Sciences, University of Toronto, Toronto, Canada

Objectives

The present research aims to investigate functional connectivity within cortical auditory networks involved with listening in children who are deaf and receive bilateral cochlear implants simultaneously in order to hear. It seeks to determine and characterize differences in auditory system connectivity measured by electrophysiological recordings between experienced bilateral implant users and normal-hearing individuals.

Background and Rationale

Cochlear implants have become widely used to restore hearing in deaf individuals. They are effective in restoring the ability to hear sound and understand speech in a quiet environment although many implant users still have difficulty with spatial localization and hearing in noise. These difficulties may be linked to crude frequency representation and insufficient integration of binaural cues from two independent implants.

The brain is known to be adaptive and undergo reorganization, especially in young children. Studies have demonstrated that naïve auditory cortices in deaf individuals show different activation compared to the auditory cortices of their experienced counterparts. The brain is made of distinct networks that support specific higher-level processes. A goal of the proposed connectivity analysis is to understand the relationships within these networks and differences between implant users and normal hearing individuals.

Methods

In this project, the connectivity of the auditory system and cortex will be evaluated using 64-channel electroencephalography (EEG) in order to draw conclusions about how an individual with cochlear implants hears.

EEG was used to record 1-second auditory evoked potentials from normal-hearing children and a bilaterally implanted cohort. Cortical activity will be considered with respect to the canonical frequency bands: Delta, Theta , Alpha, Beta, and Gamma, which are associated with specific cognitive activities. A spatial filtering method will be used to attribute the EEG data recorded from the scalp to 90 atlas-guided anatomical sources within the brain. Correlational connectivity analyses will be performed for the neural sources pairwise, within each frequency band, to show functional relationships between these regions.

Results

The cortical network activity seen in children using bilateral cochlear implants will be compared with normal hearing subjects. Frequency content, location(s) in cortex, strength of connectivity, and the temporal dynamics of these features will be used to characterize the responses.

Significance

This work should help determine the remaining challenges and factors preventing binaural hearing and ultimately help target therapies to help children adapt to their cochlear implants. The goal is that in the future, implant users will be able to take advantage of the neural processing that normal-hearing listeners use to filter out meaningful sounds in real-world environments.