Electrocochleography recorded via the Advanced Bionics cochlear implant system.

The University of North Carolina has demonstrated the ability to record ECochG via the intra-cochlear electrode array for an acoustically delivered low-frequency sinusoidal stimulus. This study examines the recording of ECochG via the complete Advanced Bionics cochlear implant system. ECochG was recorded from 20 adult subjects during and following implantation of the Advanced Bionics HiRes90K and Ultra implants. Subjects had at least one pre-operative threshold of better than 80 dBHL. During insertion of the array, recordings were made for 50 ms 500 Hz tone burst. Following insertion, recordings were made, for 125, 250 and 500 Hz tone bursts. Typically 64 averages were used for each individual measurement. Subtraction of recordings allowed extraction of the cochlear microphonic (CM) signal. Comparisons were made between the CM and behaviourally measured hearing thresholds. Analysis was also made of CM amplitude during insertion of the electrode array and correlated with the surgical reports. It was possible to record ECochG in all cases for at least one stimulus frequency. The average electrode insertion took approximately 30 seconds. A highly significant correlation (r^2 = 0.75) was found between ECochG and behavioural estimates of low-frequency hearing threshold. Changes in CM amplitude during electrode array insertion were very largely in line with surgical comments and surgical video review. Correlations between ECochG and post-implant speech perception are currently being accumulated. It appears practical to record ECochG both intra- and postoperatively using the standard Advanced Bionics cochlear implant system hardware. Recording speed is sufficient to give surgical feedback during electrode array insertion. A strong correlation exists between objective and behavioural estimates of low-frequency hearing thresholds. Future work should correlate the intra-operative ECochG time sequence and any change in hearing over time. [ABSTRACT FROM AUTHOR]