Impedance changes in chronically implanted and stimulated cochlear implant electrodes

Carrie Newbold*, Silvana Mergen, Rachael Richardson, Peter Seligman, Rodney Millard, Robert Cowan, Robert Shepherd

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

49 Citations (Scopus)


Objectives: Electrode impedance increases following implantation and undergoes transitory reduction with onset of electrical stimulation. The studies in this paper measured the changes in access resistance and polarization impedance in vivo before and following electrical stimulation, and recorded the time course of these changes. Design: Impedance measures recorded in (a) four cats following 6 months of cochlear implant use, and (b) three cochlear implant recipients with 1.5-5 years cochlear implant experience. Results: Both the experimental and clinical data exhibited a reduction in electrode impedance, 20 and 5% respectively, within 15-30 minutes of stimulation onset. The majority of these changes occurred through reduction in polarization impedance. Cessation of stimulation was followed by an equivalent rise in impedance measures within 6-12 hours. Conclusions: Stimulus-induced reductions in impedance exhibit a rapid onset and are evident in both chronic in vivo models tested, even several years after implantation. Given the impedance changes were dominated by the polarization component, these findings suggest that the electrical stimulation altered the electrode surface rather than the bulk tissue and fluid in the cochlea.

Original languageEnglish
Pages (from-to)191-199
Number of pages9
JournalCochlear implants international
Issue number4
Publication statusPublished - Jul 2014
Externally publishedYes


  • Access resistance
  • Cochlear implant
  • Electrical stimulation
  • Electrode impedance
  • Polarization impedance


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