Promontory Electrocochleography Recordings to Predict Speech-Perception Performance in Cochlear Implant Recipients

Abstract

Objective1) To determine the relationship of electrocochleography (ECochG) responses measured on the promontory with responses measured at the round window (RW) and various intracochlear sites. 2) To evaluate if promontory ECochG responses correlate with postoperative speech-perception performance using the cochlear implant (CI).Study DesignProspective cohort study.SettingTertiary referral center.Patients and InterventionsNinety-six adult CI recipients with no cochlear malformations or previous otologic surgery.Main Outcome Measure(s)Acoustically evoked ECochG responses were measured intraoperatively at both extracochlear and intracochlear locations. ECochG total response (ECochG-TR), a measure of residual cochlear function, was calculated by summing the fast Fourier transformation amplitudes in response to 250-Hz to 2-kHz acoustic stimuli. Speech-perception performance was measured at 3 months.ResultsThere were strong linear correlations for promontory ECochG-TR with the ECochG-TRs measured at the RW (r = 0.95), just inside scala tympani (r = 0.91), and after full insertion (r = 0.83). For an individual subject, the morphology of the ECochG response was similar in character across all positions; however, the response amplitude increased from promontory to RW (~1.6-fold) to just inside scala tympani (~2.6-fold), with the largest response at full insertion (~13.1-fold). Promontory ECochG-TR independently explained 51.8% of the variability (r2) in consonant-nucleus-consonant at 3 months.ConclusionsPromontory ECochG recordings are strongly correlated with responses previously recorded at extracochlear and intracochlear sites and explain a substantial portion of the variability in CI performance. These findings are a critical step in supporting translation of transtympanic ECochG into the clinic preoperatively to help predict postoperative CI performance.

Place Coding in the Human Cochlea

“…These amplitudes were used to generate cochlear microphonic (CM) tuning curves for each individual frequency across the entire electrode array. As described in previous studies, a significant response was defined as one whose magnitude exceeded the noise floor by 3 standard deviations [1][2][3] . The noise floor was ~0.3 μV for this series of recordings.…”

“…The cochlea is responsible for converting sound waves into electrical impulses for hearing, by spatially separating sound waves by frequency using the basilar membrane and other soft tissues. This specificity, known as cochlear tonotopy, was first detailed by Nobel Laureate Georg von Békésy 1 . While ex vivo stroboscopic photography in cadavers 1,2 , in vivo electrophysiological and pressure recordings in animals 3,4 , and post-mortem histologically-derived retrograde tracer and imaging methods in both humans and animals 5,6 have provided insights into the cochlear transduction process, they have limitations.…”

“…While ex vivo stroboscopic photography in cadavers 1,2 , in vivo electrophysiological and pressure recordings in animals 3,4 , and post-mortem histologically-derived retrograde tracer and imaging methods in both humans and animals 5,6 have provided insights into the cochlear transduction process, they have limitations. These include inherent artifacts and spatial limitations resulting from surgical modifications and histologic processing 1,7 , difficulty studying cochlear amplification ex vivo 8 , anatomical and physiological differences between animal models and humans 9 , and inability to replicate dynamic biologic changes affecting passive cochlear mechanics in cadavers 10 . Therefore, little is known about how the human cochlea responds in vivo to various acoustic stimuli.…”

“…Does creating an artificial cochlear 'third-window' alter the frequency-position map? Von Békésy observed the traveling wave ex vivo using a rubber membrane-cemented brass ring as an artificial stapes and a fenestration near the cochlear apex 1,7,22 . While the possibility of lowfrequency stimulation artifact as a result of the fenestration has been acknowledged 1,7,22 , the impact of the third window in vivo within the human cochlea is unknown.…”

“…Von Békésy observed the traveling wave ex vivo using a rubber membrane-cemented brass ring as an artificial stapes and a fenestration near the cochlear apex 1,7,22 . While the possibility of lowfrequency stimulation artifact as a result of the fenestration has been acknowledged 1,7,22 , the impact of the third window in vivo within the human cochlea is unknown. To investigate this, the same electrode array described above was inserted into the round window of the cochlea during a translabyrinthine approach to remove a vestibular schwannoma in a human with good residual hearing.…”