Measurements and models of auditory nerve spike rate and timing to electrical stimulation

Physiological measurements of the response of auditory nerve (AN) fibers to electrical stimulation from a cochlear implant (CI) have in general exhibited much higher maximal entrainment rates and higher temporal precision than is observed for acoustical stimulation. However, it appears that this superior rate coding in the AN for electrical stimulation does not translate to better coding of rate in the midbrain or for the percept of temporal pitch. Similarly, the enhanced temporal precision for electrical stimulation does not lead to improved coding of interaural timing differences. In this talk, I will review physiological data and computational model simulations that indicate that the superior spike rate and timing representation for CI stimulation may only hold when considering the response of some single AN fibers to repeated identical stimuli. In fact, there is a large heterogeneity in spiking responses that can change dramatically as a function of stimulus current level. A multi-compartmental computational model will be used to demonstrate how the electrode- fiber geometry and the membrane biophysics could be contributing to these phenomena. I will also discuss the implications of the likely population response of the AN to CI stimulation for brainstem processing. [Work supported by NSERC Discovery Grant 261736.]