Responses of the Auditory Nerve to High Rate Pulsatile Electrical Stimulation

Abstract

The new speech-processing strategy, the so called “Continuous Interleaved Sampling” (CIS) strategy, used in cochlear implant subjects is based on a paradigm of stimulation at high rates where 1000-1500 pulses/s (pps) are used on each channel (Wilson et al., 1991; McDermott et al., 1992). Recent psychophysical studies on cochlear implant subjects have demonstrated, with the CIS as compared to previous paradigms of stimulation, an improvement in speech perception (Wilson et al., 1991; McDermott et al., 1992; Pelizzone et al., 1995). However, electrical stimulation of the auditory nerve (AN) at such high rates will affect its responses because of the neurons’ refractory period. Furthermore, prolonged electrical stimulation at high rate might influence neurons’ metabolism, possibly leading to fatigue. Therefore, study on the physiological behavior of the AN when stimulated by cochlear implant at higher rates is important to better understand the speech coding procedure, as well as to provide insight into the safety of such new speech processing strategy. A cochlear implant animal model has been established in the rat (Hall, 1990; Vischer et al., 1994; Zhang et al, 1996), in order to address such issues that might not be conducted routinely in patients.