Musical training seems to improve pitch perception ability in prelingually deafened children with a cochlear implant. Auditory plasticity might play an important role in such enhancement. This suggests that incorporation of a structured training program on music perception early in life and as part of the postoperative rehabilitation program for prelingually deafened children with cochlear implants would be beneficial. A longitudinal study is needed to show whether improvement of music performance in these children is measurable by use of auditory evoked potentials.

Previous animal study revealed that post-implantation electrical detection levels significantly declined within days. The impact of cochlear implant (CI) insertion on human auditory pathway in terms of impedance and electrically evoked compound action potential (ECAP) variation within hours after surgery remains unclear, since at this time frequency mapping can only commence weeks after implantation due to factors associated with wound conditions. The study presented our experiences with regards to initial switch-on within 24 hours, and thus the findings about the milieus inside cochlea within the first few hours after cochlear implantation in terms of impedance/ECAP fluctuations. The charts of fifty-four subjects with profound hearing impairment were studied. A minimal invasive approach was used for cochlear implantation, characterized by a small skin incision (≈2.5 cm) and soft techniques for cochleostomy. Impedance/ECAP was measured intro-operatively and within 24 hours post-operatively. Initial mapping within 24 hours post-operatively was performed in all patients without major complications. Impedance/ECAP became significantly lower measured within 24 hours post-operatively as compared with intra-operatively (p<0.001). There were no differences between pre-operative and post-operative threshold for air-conduction hearing. A significant drop of impedance/ECAP in one day after cochlear implantation was revealed for the first time in human beings. Mechanisms could be related to the restoration of neuronal sensitivity to the electrical stimulation, and/or the interaction between the matrix enveloping the electrodes and the electrical stimulation of the initial switch-on. Less wound pain/swelling and soft techniques both contributed to the success of immediate initial mapping, which implied a stable micro-environment inside the cochlea despite electrodes insertion. Our research invites further studies to correlate initial impedance/ECAP changes with long-term hearing/speech performance.

ObjectivesChanges in impedance between 24 hours and one month after cochlear implantation have never been explored due to the inability to switch on within one day. This study examined the effect of early activation (within 24 hours) on the evolution of electrode impedance with the aim of providing information on the tissue-to-electrode interface when electrical stimulation was commenced one day post implantation.MethodsWe performed a retrospective review at a single institution. Patients who received a Nucleus 24RECA implant system (Cochlear, Sydney, Australia) and underwent initial switch-on within 24 hours postoperatively were included. Impedance measurements were obtained intraoperatively and postoperatively at 1 day, 1 week, 4 weeks, and 8 weeks.ResultsA significant drop in impedance was noted 1 day after an initial activation within 24 hours followed by a significant rise in impedance in all channels until 1 week, after which the impedance behaved differently in different segments. Basal and mid-portion electrodes revealed a slight increase while apical electrodes showed a slight decrease in impedance from 1 week to 8 weeks postoperatively. Impedance was relatively stable 4 weeks after surgery.ConclusionsThis is the first study to report the evolution of impedance in all channels between initial mapping 1 day and 1 month after cochlear implantation. The underlying mechanism for the differences in behavior between different segments of the electrode may be associated with the combined effect of dynamics among the interplay of cell cover formation, electrical stimulation, and fibrotic reaction.