fMRI of Cochlear Implant Candidates

Children with severe sensorineural hearing loss now have new possibilities for improvement in their ability to hear and communicate with new technology called Cochlear Implantation. However, not all children experience the same benefit from Cochlear Implantation, with the outcome often being unpredictable, especially in children born deaf, or in whom hearing loss occurred at a very young age. We are investigating the use of functional MRI in children with profound sensorineural hearing loss to determine if residual auditory cortical activity may be observable. Our hope is to use fMRI to guide decision making about cochlear implantation in children.

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As with cortical blindness, if the auditory cortex is not stimulated during the first 0-2 years of life, the window of opportunity is closed. Subsequently the ability to process auditory information is lost. Current methods of evaluating candidates for cochlear implantation involve audiology, auditory brainstem evoked potential response (ABR), and otoscopic examination of the middle and inner ear. The ability to reliably select candidates who will benefit from the surgical procedure is poor.

Accordingly, we are now using fMRI to solve the puzzle and to show that positive outcome of cochlear implantation in young children with pre-lingual profound sensorineural hearing loss relates to the amount of residual representation for hearing in primary auditory cortex of these children. FMRI may provide a tool for predicting outcome from cochlear implantation and establish a new clinical criterion for selection of implant candidates.

The activation pattern obtained from a 12 year old cochlear implant candidate listening to random tones is shown in Figure 1. The subject had total hearing loss in the left ear. There was some hearing in the right ear with severe tinnitus. However bilateral activation is present in the auditory cortex. This would suggest that the subject still retains some sensorineural hearing ability in the left ear.

One obstacle in performing fMRI on cochlear implant candidates is that it will be necessary to sedate many of the subjects due to their young age. The sedation must be performed in such a manner as to preserve functional activation in the auditory cortex. Figure 2 shows the activation pattern obtained from a 5 year old boy sedated with Nembutal while listening to random tones. There is very robust activation in the auditory cortex and thus Nembutal appears to be a promising method of sedation.

We are investigating the cortical blood flow response and BOLD effect in children under sedation with various agents. If we can develop reliable methods for performing fMRI of sensory stimulation tasks in sedated children, it will be possible to investigate brain disorders at a much early period of development.