Despite the success of cochlear implants (CIs) in human populations, most users perform poorly in noisy environments and music and tonal language perception. How CI devices engage the brain at the single neuron level has remained largely unknown, in particular in the primate brain. By comparing neuronal responses with acoustic and CI stimulation in marmoset monkeys unilaterally implanted with a CI electrode array, we discovered that CI stimulation was surprisingly ineffective at activating many neurons in auditory cortex, particularly in the hemisphere ipsilateral to the CI. Further analyses revealed that the CI-nonresponsive neurons were narrowly tuned to frequency and sound level when probed with acoustic stimuli; such neurons likely play a role in perceptual behaviors requiring fine frequency and level discrimination, tasks that CI users find especially challenging. These findings suggest potential deficits in central auditory processing of CI stimulation and provide important insights into factors responsible for poor CI user performance in a wide range of perceptual tasks.
Bibliographical noteFunding Information:
This work was supported by National Institutes of Health National Institute on Deafness and Other Communication Disorders Grat R01DC014503 to X.W., Grant F31DC010321 to L.A.J., and Grant P30 DC005211 to the Center for Hearing and Balance at Johns Hopkins University, and a grant from the Kleberg Foundation to X.W.Wethank J. Estes and N. Sotuyo for help with animal care; P. Loizou and D. Kim (University of Texas Dallas) for providing the cochlear implant stimulator current source; and Z. Smith (Cochlear Limited) for assistance obtaining implant electrodes.
© 2016 the authors.
- Auditory cortex
- Cochlear implant