Abstract

Background and Objectives: Current multichannel vestibular prosthesis under development has problems to overcome, for example, electrical currents easily spread over the adjacent ampullae such as horizontal and superior canal ampullae and there is asymmetry between excitation and inhibition response due to the characteristics of vestibular nerve. Pulsed infrared radiation (IR) is known for more spatially selective stimulation of cranial nerve than electric current. We stimulated crista ampullaris of chinchilla with IR to collect various responding vestibular afferents from single unit recordings.
Materials and Methods: Adult female chinchillas (450-650 g) were used in this study. After exposure of superior vestibular nerve for single unit recording, we opened a hole at the lower part of superior semicircular canal (SCC) to introduce the optical fiber (400 μm in diameter) over the crista ampullaris. IR photo-stimulation was delivered using Capella pulsed infrared laser (Lockheed-Martin Aculight, Bothell, WA, USA) with optical fiber (400 μm in diameter).
Results: We’ve recorded total 49 units from SCC consisted of superior (n=19) and horizontal (n=30). Among them, there were three kinds of responses from regular afferents (excitation [n=17], inhibition [N=12], and mixed [N=6]) and two kinds of responses from irregular afferents (excitation [N=5] and inhibition [N=9]) in this study. Regular afferents showed pretty small time constants that were less than 1 sec and irregular afferents had abrupt rise (excitation) and shut-down (inhibition) responses. During recording phase-locking responses from excitatory irregular afferents, there were 2.1±3.5 msec between neuronal responses and laser pulses. Pulse width and pulse rate of IR modulated afferent responses according to the sum of energy, while the wavelength over 1,863-1,877 nm had little or no effect.
Conclusion: From these results, we showed that IR photo-stimulation could modulate various responses from stimulation of crista ampullaris of mammals, which consisted of 5 different responses from regular and irregular afferents including phase-locking responses.