gms | German Medical Science

One of the factors that may affect the individual outcome of cochlear implantation is the degree of survival of auditory nerve fibres. This factor may also be relevant to the processing strategy (or rate of stimulation) that optimises performance for an individual. This paper presents the results of a study with 18 guinea pigs, in which the effects of pulse phase duration (PD) and interphase gap (IPG) on the amplitude of the electrically-evoked compound action potential (ECAP) and auditory brainstem response (EABR) were measured. The guinea pigs were deafened and acutely implanted with an electrode array after 1 to 12 weeks of deafness. The spiral ganglion cell density was significantly correlated with the effects of PD and IPG on EABR, and the effect of IPG on ECAP. The effects of PD and IPG on EABR, ECAP (measured using neural response telemetry), and psychophysical loudness were also measured in a group of adult implantees. The effects of IPG and PD varied among implantees over the same range measured in the animals. Furthermore, the measurements in implantees were correlated with each other, supporting the proposition that the measures are affected by a common underlying factor (such as degree of survival). These experiments showed that it appears possible to assess neural survival in implantees, and this will allow the impact of variations in neural survival on performance to be studied.