Vestibular peripheral function remains robust after two weeks of continuous ionic direct current stimulation.

Abstract


Conventional neural prostheses use brief charge-balanced pulses to minimize the risk of electrode polarization and irreversible electrochemistry at the electrode-electrolyte interface, constraining the waveforms that can be delivered long-term. Direct current (DC) stimulation has shown advantages, such as direct excitation and inhibition of tissue, but prior in vivo reports have been largely limited to acute durations. This study explores the physiological and histological effects of prolonged DC stimulation at amplitudes effective for neuromodulation while isolating tissue from the electrode-electrolyte interface. 
Approach:
We developed a separated interface nerve electrode (SINE) device for long-term ionic direct current (iDC) stimulation in free-roaming rodents. Using our device, we applied 14 days of continuous iDC targeting the vestibular periphery in nine chinchillas. We measured vestibulo-ocular reflex responses to iDC before and after stimulation. Postmortem, we performed a histological comparison of stimulated ears and implanted but unstimulated controls.
Main results:
All chinchillas retained robust vestibular reflex function after 14 days of continuous iDC at up to 30 µA. Histological exam found no differences associated with iDC stimulation between the stimulated ears and the implanted but unstimulated ears.
Significance:
Decoupling the metal-electrolyte interface from the target tissue enables prolonged delivery of iDC at amplitudes effective for neuromodulation without causing a loss of physiologic responses or histologic signs of structural damage.&#xD.