Polarity effects on neural responses of the electrically stimulated auditory nerve at different cochlear sites

Abstract

Three experiments studied the effect of stimulus polarity on the Electrically Evoked Compound Action Potential (ECAP) obtained with the masker-probe paradigm on different sites along the cochlea in cochlear implant users. Experiment 1 used a biphasic cathodic-1st (BIC) masker and showed that ECAP N(1) peak latencies were longer for BIC than for biphasic anodic-1st (BIA) probes on all electrodes under test. Both the latency of each probe as well as the latency difference between BIA and BIC probes increased when the phase width (PW) of the masker and probe were increased together. Experiment 2 used maskers with long inter-phase gaps (IPGs), and, by manipulating the polarity of the second phase (closest in time to the biphasic probe), showed that only an anodic phase could mask the probe response. Experiment 3 used maskers and probes with long IPGs and measured ECAPs to the first phase of the probe; ECAPs could be measured when both this phase and the second phase of the masker were anodic, but not when they were cathodic. Our results extend those of a previous study, showing that the auditory nerve in humans is preferentially activated by anodic stimulation, to different sites along the cochlea.

Spread of excitation varies for different electrical pulse shapes and stimulation modes in cochlear implants

“…Following the results by Macherey et al (2008) and Undurraga et al (2010) obtained in MP mode, the present results show that BP þ 3 PS, RPS and SYM-IPG maskers strongly excited AN fibers close to the masker electrode that delivered the effective anodic pulse. Macherey et al (2010) measured forward-masking excitation patterns in human CI users.…”

“…Their results showed that anodic stimulation was necessary for an ECAP to be observed. Further research demonstrated that this finding is generalized along the cochlea (Undurraga et al, 2010). However, it may be that different stimulation modes (see Sec.…”

“…With respect to polarity sensitivity of the human AN, recent behavioral (Macherey et al, 2006) and objective (Macherey et al, 2008;Undurraga et al, 2010) studies have shown that the anodic phase is the most effective phase in human CI users. By using PS pulses, Macherey et al (2006) have found that PSA pulses have lower Comfortable Levels (CLs) than PSC ones.…”

“…Reasons of high sensitivity to the anodic polarity have been discussed in detail by Macherey et al (2008) and Undurraga et al (2010). The most likely excitation sites in a healthy AN fiber are:…”

Tinnitus Suppression by Intracochlear Electrical Stimulation in Single-Sided Deafness: A Prospective Clinical Trial - Part I

“…However, caution is required as anodic first stimulation was applied only twice per subject. A difference in tinnitus suppression between cathodic and anodic first charge-balanced electrical stimulation was initially expected as prior studies showed that anodic stimulation could be more sensitive than cathodic stimulation [Undurraga et al, 2010[Undurraga et al, , 2013Carlyon et al, 2013]. The cathodic phase is thought to stimulate the peripheral process while the anodic phase probably excites the nerve fibers more centrally [Rattay et al, 2001].…”