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Potential benefits from deeply inserted cochlear implant electrodes
1Audiology & Deafness Research Group, School of Psychological Sciences, University of Manchester, Manchester, United Kingdom. boyd.diag.audiol@btinternet.com
Ear and Hearing
|January 21, 2011
Summary
Longer cochlear implant electrodes may offer some benefits for hearing perception, but evidence is mixed. Deeper insertion can cause cochlear trauma, potentially impacting long-term outcomes and residual hearing.
Area of Science:
- Otorhinolaryngology
- Biomedical Engineering
- Neuroscience
Background:
- Cochlear implant electrode arrays typically extend 1-1.5 turns from the cochleostomy.
- Longer arrays aim to provide additional low-frequency auditory percepts and increase spectral information.
- One manufacturer (MED-EL) utilizes longer electrode arrays, with experimental versions developed by others.
Purpose of the Study:
- To review evidence on the potential benefits of cochlear implant electrodes extending into the apical cochlear regions.
- To examine underlying issues including cochlear anatomy, electrode design, and surgical considerations.
- To draw general conclusions about apical electrodes rather than specific device performance.
Main Methods:
- Review of imaging studies on electrode insertion depth.
- Assessment of anatomical and modeling studies.
- Examination of pitch scaling trials and performance studies.
- Consideration of surgical trauma and long-term consequences.
Main Results:
- Current electrode arrays rarely exceed two turns (mean insertion ~630°), shorter than the cochlea's full length.
- Longer electrodes may stimulate discrete neural populations near the apex.
- Pitch scaling studies show success in many cases, but pitch confusions/reversals occur in a significant number of individuals.
- Evidence suggests longer arrays may cause more intracochlear trauma, impacting residual hearing and neural substrate.
Conclusions:
- Benefits of deeply inserted electrodes for speech recognition are unclear, with conflicting results from acute and chronic studies.
- While some studies suggest performance benefits, others show improvement after deactivating apical electrodes.
- Potential long-term consequences include loss of residual hearing and neural substrate reduction.
- A clinical dilemma exists as patients who might benefit most from apical electrodes may also benefit from bimodal electroacoustic stimulation requiring shallower insertion.
