Journal Club: Electrically evoked potential recording from vestibular nerves through vestibulo-cochlear implants.

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Today's journal article

van Boxel SCJ, Vermorken BL, Volpe B, Guinand N, Perez-Fornos A, Devocht EMJ, van de Berg R. Exploring applications of electrically evoked compound action potentials using the vestibulo-cochlear implant. 

Why I picked this article

Our vestibular system is responsible for sensing the motion and orientation of our head. Peripheral vestibular organs are located in the inner ear, alongside the hearing organ, the cochlea. To understand pathology in the peripheral vestibular system in both animal models and humans, and to develop treatment for those pathologies, functional testing of the vestibular system is important. 

Electrically evoked compound action potentials (eCAPs) are recorded from nerve fibres in response to electrical stimulation. eCAP can be evoked by using electrodes for stimulation, and recording from other electrodes. eCAP is used for the functional assessment of the cochlea in the context of a cochlear implant. 

This research was part of a clinical trial investigating a newly developed vestibulo-cochlear implant, aimed to restore function of the peripheric vestibular system and the cochlea. As part of this and making the surgery more effective for the future, this research aims to investigate the use of eCAP as the measure of vestibular system function, with the view that this may become a tool to facilitate effective use of vestibular implants. In particular, the research asks how well vestibular eCAPs predict functional outcomes like the electrically evoked vestibulo-ocular reflex (eVOR) and cross-talk with the cochlea. 

Some of the research findings

Study design:
  • This research was part of VertiGo!-trial (ClinicalTrials. gov Identifier: NCT04918745)
  • 10 bilateral vestibulopathy patients with severe sensorineural hearing loss 
  • Received an investigational vestibulo-cochlear implant (MED-EL) on one ear, except one subject who received bilaterally. 
  • The implant: 
  • Three vestibular electrode leads inserted to each of ampula. 
  • electrode array inserted in the cochlea (9 channels) 
 eCAP measurement:
  • eCAPs recorded intra-/peri-operatively across configurations.
  • Configurations tested: 
    • trans-canal (one electrode in the canal as stimulating electrode, another in the canal as recording electrode) 
    • vestibulo-cochlear 
    • cochleo-vestibular
  • Nerve targetted for eCAP
    • L = lateral ampullary nerve
    • S = superior ampullary nerve
    • P = posterior ampullary nerve
  • Outcomes compared against eCAPs: eVOR presence, eVOR misalignment (degrees), auditory percept during vestibular stimulation, vestibular activation during cochlear stimulation.
Findings
  • The presence of vestibular eCAP predicted the presence of an eVOR very well. 
  • On the other hand, the lack of vestibular eCAP did not necessarily mean a lack of eVOR. 
  • Low negative predictor value means it may not be very useful for evaluating electrode positioning intraoperatively. 
  • Presence/size of trans-canal eCAP did not correspond to eVOR misalignment. 
Figure 2 from Boxel et al. 2025. 

Haruna's takeaway

Vestibulo-cochlear implant is here! It appears that this part of the larger study is evaluating the Vestibulo-cochlear implant in the clinical trial phase. Cochlear implants are often described as one of the most successful bionic implants and have been adopted across the globe to restore the sense of hearing. We have been hearing about vestibular implants in the pipeline for the last few years, with now publications coming through. Vestibular disorder can be very debilitating, and implants that could provide relief could be life-changing for those affected. I am very keen to watch this space! On the side note, I am interested in the use of eCAP is interesting, and I would be very keen to try ones ourselves one day - on sheep!  

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This is Haruna's 54/100 of the 100-day challenge to post a science blog article every day! I love inner ear biology & cochlear physiology.