Summating Potential as Marker of Intracochlear Position in Bipolar Electrocochleography

Area of Science:

• Otoacoustic emissions and electrophysiology
• Auditory neurophysiology
• Medical device engineering

Background:

• Cochlear implantation (CI) requires precise electrode placement to preserve residual hearing.
• Minimizing trauma and avoiding unwanted stimulus interactions are key surgical goals.
• Existing methods for monitoring residual hearing during implantation have limitations.

Purpose of the Study:

• To investigate the efficacy of intracochlear, bipolar summating potential (SP) recordings for determining cochlear implant (CI) contact position.
• To validate SP-based position estimates using micro computed tomography (µCT) and anatomical reconstructions.
• To propose a simplified surgical monitoring method using SP recordings.

Main Methods:

• Investigated bipolar SP recordings in guinea pig cochleae (n=13) during CI insertion.
• Utilized SP polarity reversals as a functional marker for intracochlear electrode position.
• Correlated SP-based position estimates with µCT imaging and a modified Greenwood function for cochleotopic mapping.

Main Results:

• SP-based position estimation achieved an average precision of ±0.37 octaves.
• Position estimation accuracy was unaffected by moderate noise-induced hearing loss.
• Cochleotopic position of the CI explained approximately 70% of the SP polarity reversal variability.

Conclusions:

• Bipolar SP recordings offer reliable intraoperative feedback on electrode position within the cochlea.
• The technique's precision is maintained even with post-implantation hearing impairment.
• This method can guide CI surgery to target specific cochlear frequency regions, preserving residual hearing.