CI Neural Mechanisms

PROJECT SUMMARY/ABSTRACT Cochlear implants (CIs), which directly stimulate the auditory nerve (AN), are widely considered to be the most successful neuroprosthetic device. However, patients with CIs do not understand speech as well as people with normal hearing, and there remains an unmet clinical need to improve performance in established CI users. CIs are adjusted for each listener by varying the stimulus parameters on each electrode (“programming”); however, programming techniques have largely remained unchanged since CIs were first approved by the FDA in 1984. Studies have shown that 1) the estimated density of AN fibers affects speech recognition outcomes in CI users, 2) AN density can be estimated at each electrode site in CI users, and 3) speech recognition improves for some CI users when stimulating electrode sites with higher AN density. While these studies show that speech recognition seems to be at least somewhat dependent on the ability of AN to precisely code the signal, encoding of information at the level of the auditory cortex is also important for adequate speech understanding. The present studies will define the role of AN density in the precise coding of “timing” (temporal) information and quantify the extent to which stimulating electrodes with higher AN density affects encoding of temporal information at the level of the auditory cortex. We hypothesize that users will show improved speech understanding when using a CI program that stimulates electrodes with higher AN density, but these improvements will be associated with more precise encoding of temporal cues within the auditory cortex.