Perceptual implications of cochlear implant electrode-neuron interfaces

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Project Summary/Abstract Cochlear implants are highly successful neural prostheses that enhance or restore audition to severely hearing-impaired adults and children. Sound from the environment is converted into electrical pulses and conveyed to the auditory nerve by an array of electrodes. The cochlear implant provides important spectral and temporal information to the listener. However, speech perception performance varies considerably among cochlear implant listeners, particularly in noisy environments and for complex stimuli. This variability exists even for children who receive their cochlear implants early in development (<2 years old). Recent evidence suggests that children have a higher density of healthy auditory neurons, which are the target of stimulation through an implant. There is also a critical period for auditory developmental plasticity. The interaction of these factors and the chronic electrical stimulation of a cochlear implant are not well understood, especially for early-implanted children. Despite these known differences between adults and the immature auditory systems of children, cochlear implant research has focused on adults. In adults, the most promising methods for optimizing programming strategies include focusing the electrical field emitted by each electrode to stimulate a more restricted population of neurons and deactivating less effective electrodes. Very few attempts have been made to optimize programming strategies specifically for children, and recent evidence suggests children would benefit more than adults from focused stimulation. Moreover, when new programming strategies are implemented, there is limited data about the timecourse needed to assess their effectiveness. Three aims are proposed: 1) Determine the underlying mechanisms for spectral resolution in children and adults with cochlear implants by comparing peripheral physiological and behavioral tuning across the lifespan; 2) Quantify short-term changes (over hours) in speech perception in children and adults when using optimized programming strategies with selective channel deactivation with and without focused stimulation; and 3) Quantify long-term changes (over weeks) in speech perception in children and adults using the same optimized strategies as in Aim 2. The results of the proposed studies are expected to advance our understanding of how the implanted auditory system develops, how cochlear implants should be programmed to best deliver spectrally challenging signals, and the timecourse of acclimatization to changes in programming strategies. These findings could guide clinical decision making about when to make programming adjustments, what types of adjustments to make, and how long patients need to reach peak performance following adjustments. The results from these studies could ultimately lead to improved functional outcomes for children and adults with cochlear implants.