Hypothesis: Extracochlear electric-acoustic stimulation (EAS) between the round window membrane and the basal part of the cochlear bone exhibits distinct auditory brainstem response (ABR) characteristics.
Background: The use of EAS in individuals with residual hearing is becoming increasingly common in clinical settings. Ongoing research has explored the characteristics of EAS-induced responses in hearing cochleae.
Methods: This study explored a novel extracochlear EAS approach using round window membrane-cochlear bone stimulation to maintain cochlear integrity. The electrodes stimulate the basal part of the cochlea and spare the apex, making the model ideal for EAS candidates with profound high-frequency hearing loss and residual low-frequency hearing. ABR analyses of EAS were conducted to compare responses to acoustic, electrical, and combined stimulations.
Results: The threshold of EAS was higher than that of acoustic stimulation (AS) or electric stimulation (ES). The maximum peak height of the amplitude (MPHA) in the EAS showed sound pressure level (SPL)- and electric current-dependent changes, with superior performance at higher SPLs. The MPHA latency shift index analysis demonstrated significant differences between the EAS and the AS or ES only. In the context of EAS, neural responses occurring before 4 ms are defined as early responses, which are related to the stimulus. Late responses, occurring after 4 ms, suggest distinct physiological mechanisms that may involve synaptic actions or specific interactions within the EAS.
Conclusion: Extracochlear EAS provides insights into its physiological implications, proposes a method for clinical application, and offers a potential avenue for improving hearing preservation and performance.
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