Combined ionic direct current and pulse frequency modulation improves the dynamic range of vestibular canal...

Area of Science:

• Neuroscience
• Biomedical Engineering
• Ophthalmology

Background:

• Vestibular prostheses aim to restore vestibular function using pulse frequency modulation (PFM) to stimulate semicircular canals.
• Spontaneous vestibular nerve activity can restrict the dynamic range of PFM-evoked responses.
• Ionic direct current (iDC) is proposed to inhibit spontaneous nerve activity, potentially expanding the dynamic range.

Purpose of the Study:

• To investigate if a tonic iDC baseline enhances the dynamic range of eye responses evoked by PFM in vestibular prostheses.
• To test the hypothesis that co-applying iDC with PFM improves vestibular stimulation efficacy.

Main Methods:

• Experiments were conducted on gentamicin-treated chinchillas with microcatheter electrodes implanted in the vestibular semicircular canals.
• Both pulsatile and iDC were delivered through the electrodes.
• The vestibulo-ocular reflex (VOR) was modulated by PFM, adapted to a preset iDC and pulse-frequency baseline, and evoked eye responses were recorded.

Main Results:

• PFM stimulation successfully produced VOR responses aligned with the stimulated canal.
• The introduction of a tonic iDC baseline resulted in a statistically significant increase in eye response velocity.
• The direction of eye rotation remained unaffected by the iDC baseline.

Conclusions:

• Tonic iDC baselines can effectively increase the dynamic range of head velocity encoding during pulsatile stimulation.
• This improvement is potentially achieved by inhibiting spontaneous activity in the vestibular nerve.
• The findings suggest iDC is a promising adjunct for enhancing vestibular prosthesis performance.