Neuroscience of the Pediatric Auditory Brainstem Implant

When prosthetic sound information is supplied by electrodes to the auditory nerve or auditory brainstem, the pattern of nerve activity in the brain is highly unnatural compared with the normal acoustic pattern of activation. How does the brain respond to and incorporate this unnatural pattern of activity? The answer depends on the place of stimulation (cochlea, brainstem, midbrain, cortex), the residual health of the stimulated neurons (intact or damaged), the age of the individual when they receive the stimulation (young or older), and their prior experience with sound before hearing loss (congenital vs. acquired loss). This chapter discusses the history of perception when sensory function is restored in both hearing and vision. Early philosophers thought that perceptual pattern perception was “preordained,” and so once sensory input was restored, the person should have an immediate function. In the 1700s, European philosophers argued that perception was determined by experience so that once sensory function was restored, people would have to learn to hear or see from the beginning. We now know that this latter idea is correct from our recent experience with hearing and vision restoration. In this chapter, we discuss the implications of cochlear implants (CIs) and auditory brainstem implants (ABIs) for guiding our understanding of the interaction between the sensory system and the brain. CIs provide a degraded but tonotopically organized representation of sound information to the brain, while ABIs provide a degraded and tonotopically scrambled pattern of information to the brain. We discuss CI and ABI outcomes in adults and children, both congenitally and postlingually deafened adults and children. The contrasts and similarities in outcomes across these different patient populations and devices provide an opportunity to refine our understanding of the relative roles of the sensory periphery and the brain in sensory function.