Electrically evoked auditory cortical responses elicited from individually fitted stimulation parameters in cochlear implant users

Abstract

Objective

To investigate electrically evoked auditory cortical responses (eACR) elicited from the stimulation of intracochlear electrodes based on individually fitted stimulation parameters in cochlear implant (CI) users.

Design

An eACR setup based on individual fitting parameters is proposed. A 50-ms alternating biphasic pulse train was used to stimulate apical, medial, and basal electrodes and to evoke auditory cortical potentials (N1-P2 complex).

Study sample

The eACR setup proposed was validated with 14 adult CI users.

Results

Individual and grand-average eACR waveforms were obtained. The eACR amplitudes were lower in the basal than in the apical and medial regions. Earlier N1 latencies were found in CI users with lower maximum comfortable loudness levels and shorter phase duration in response to apical stimulation, while medial and basal stimulation resulted in earlier N1 latencies and larger N1-P2 amplitudes in users with longer CI experience.

Conclusions

eACR could be elicited by direct intracochlear stimulation using individual fitting parameters with a success rate of 71%. The highest cortical peak-to-peak amplitudes were obtained in response to apical stimulation. Unlike the P2, the N1 component appeared to be a consistent cortical potential to determine eACR and gain knowledge of the auditory processing beyond the cochlea in CI users.

Highlights

• eACR can be elicited through direct stimulation of intracochlear electrodes.

• Stimulation of apical and medial regions yielded the highest N1-P2 amplitudes.

• CI users with lower maximum comfortable loudness levels had shorter N1 latencies during apical stimulation.

• The present dataset of mainly well-performing CI users suggests better cortical processing, that is, higher amplitudes and shorter latencies of N1.

• The N1 potential appears a more consistent and reliable potential than the P2 to determine eACR responses in CI users.

Keywords:

• Electrically evoked cortical responses
• fitting stimulation parameters
• N1-P2
• electrical stimulation
• objective measures
• intracochlear electrodes

Acknowledgements

We would like to thank the CI users who volunteered their time and the staff of Hospital Universitario Virgen Macarena for their help in carrying out the eACR recordings. We also thank Giacomo Mandruzzato (MED-EL) for his helpful comments and Angelina Gurkina (MED-EL) and David Plant for language and style help on a version of this manuscript.

Author contributions

Conceptualisation: M.A.C.-L., M.M.B.-R, A.K, S.S.-G.; Methodology: M.A.C.-L., M.M.B.-R, A.K, A.J.B.; Formal analysis and investigation: M.A.C.-L., M.M.B.-R; Writing: M.A.C.-L., M.M.B.-R, A.K; Original draft preparation: M.A.C.-L., M.M.B.-R; Writing, review and editing: M.A.C.-L., M.M.B.-R, A.K, A.J.B.; Funding acquisition: S.S.-G.; Resources: S.S.-G., A.K; Supervision: A.J.B.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data available on request from the authors.

Additional information

Funding

This study was funded by the Spanish ISCIII Health Research Institute under the project DTS21/00180 co-financed by the European Union, and by the Consejería de Salud y Familias, Andalusia Government, under the project PIER-0365-2019.