Neural degeneration alone does not explain polarity sensitivity differences in cochlear implants

Evidence

If neural degeneration had an effect on polarity sensitivity, we would expect the polarity effect to increase over time and to reach positive values when fibers are degenerated. This does not seem to be the case as the level difference between polarities rather tends to decrease right after deafening for several subjects and then to remain roughly constant. — Dijk, Pim van, Physiology, Psychoacoustics and…, 2309

Most guinea-pigs tested in the present study showed higher sensitivity to cathodic stimulation. This effect of polarity was consistent across all levels tested, ranging from threshold to maximum level. This observation corroborates the results obtained in most previous animal experiments performed in cats and guinea pigs. … Duration of deafness did not influence the effect of polarity, suggesting that neural degeneration may not entirely account for the higher sensitivity to anodic stimulation observed in humans. However, the morphology of the nerve fibers and the cochlear geometry are different in the two species and may play an additional role on neural excitation (Rattay et al. 2001 ). — Dijk, Pim van, Physiology, Psychoacoustics and…, 2322

Categorization

• QUESTION: Why does the polarity effect actually decrease slightly right after deafening? The mechanism behind this transient change is unexplained and worth investigating.
• XREF: Cochlear implant electrophysiology contrasts animal cathodic preference with human anodic preference — connects to broader question of species differences in neural excitation. — connects to: Neural degeneration over time does not flip cathodic-anodic stimulation efficiency in deafened guinea pigs; Anodic current outperforms cathodic current in human cochlear implant users at suprathreshold levels — Dijk, Pim van, Physiology, Psychoacoustics and…, 2275; Neural degeneration does not drive the anodic sensitivity seen in humans — Dijk, Pim van, Physiology, Psychoacoustics and…, 2272 (+8 more)
• corroborated: 4 independent passages support this claim — Dijk, Pim van, Physiology, Psychoacoustics and…, 2309; Dijk, Pim van, Physiology, Psychoacoustics and…, 2322

Broader Connections

• Cross-modal brain plasticity from deafness variably helps or harms cochlear implant outcomes #complicates (0.75) — Dijk, Pim van, Physiology, Psychoacoustics and…, 4274
• Sound localization deficits in hearing loss come from neural coding changes, not audibility. #expands (0.75)