Further prospective findings with compound action potentials from Nucleus 24 cochlear implants.

The purpose of this study was to gain greater understanding of compound action potential (CAP) specific characteristics including: slope of the growth function, P1-N1 amplitude, threshold and latencies of P1 and N1 measured in cochlear implant users. Experienced adult subjects underwent behavioral threshold (T) measurement and electrically elicited stapedial reflex (eSR) recording, followed by CAP measurements on six selected electrodes. Based on the electrically elicited stapedial reflex threshold (eSRT), maximum stimulation level for each measured electrode was set. Relationships among the three thresholds of the above measures and maximum CAP P1-N1 amplitude and slope of the growth function were statistically evaluated for each measured electrode. Threshold of the CAP response showed relationships of similar strength with eSRT and T (r=0.69 and 0.61, respectively). For both slope of the growth function and CAP P1-N1 amplitude, a statistically significant relationship with cochlear place was found. Both specific characteristics of CAP measurement for the most apical electrodes were roughly double those for the most basal electrode (alpha=0.05). This may be partially explained by cochlear anatomy and is consistent with prior mammalian and human studies showing increasing density and survival of spiral ganglion cells in the regions corresponding to intracochlear electrode placement from basal to apical electrodes (90-360 degrees ).