Optical stimulation of the hearing and deaf cochlea under thermal and stress confinement condition

Abstract

There is a controversy, to which extend cochlear stimulation with near infrared laser pulses at a wavelength of 1860 nm is based on optoacoustic stimulation of intact hair cells or -in contrast-is based on direct stimulation of the nerve cells in absence of functional hair cells. Thermal and stress confinement conditions apply, because of the pulse duration range (5 ns, 10 µs-20 ms) of the two lasers used. The dependency of the signal characteristics on pulse peak power and pulse duration was investigated in this study. The compound action potential (CAP) was measured during stimulation of the cochlea of four anaesthetized guinea pigs, which were hearing at first and afterwards acutely deafened using intracochlear neomycin-rinsing. For comparison hydrophone measurements in a water tank were performed to investigate the optoacoustic signals at different laser interaction regimes. With rising pulse peak power CAPs of the hearing animals showed first a threshold, then a positively correlated and finally a saturating dependency. CAPs also showed distinct responses at laser onset and offset separated with the pulse duration. At pulse durations shorter than physiological response times the signals merged. Basically the same signal characteristics were observed in the optoacoustic hydrophone measurements, scaled with the sensitivity and response time of the hydrophone. Taking together the qualitative correspondence in the signal response and the absence of any CAPs in deafened animals our results speak in favor of an optoacoustic stimulation of intact hair cells rather than a direct stimulation of nerve cells.

Optical wireless cochlear implants

“…A list of the advantages and disadvantages of the OWCI and RF cochlear implant (RFCI) is depicted in Table 1. It is noted that OWCI is in line with the advances in CIs, since the use of optics for the stimulation of the acoustic nerve has been recently proposed [7,[24][25][26][27][28]. In addition, we evaluate the feasibility and the capabilities of the proposed system whilst we provide design guidelines for the OWCI.…”

Infrared neural stimulation fails to evoke neural activity in the deaf guinea pig cochlea

“…This has led to some doubt about the stimulation mechanism in cochlear studies, which questions as to whether INS directly activated the SGNs, or whether SGN activation occurred as a result of hair cell mediated responses (Schultz et al, 2014). This is an important distinction for the application of INS with a cochlear implant where recipients typically have severe to profound deafness with few (if any) functional hair cells remaining.…”

Photoacoustic effect invokes auditory response in infrared neuron stimulation

“…Optoacoustic stimulation depended on the water and hemoglobin absorption, and it was related to the functionality of the HCs. 18 Later on, Schultz et al continued applying hydrophone measurements in a water tank and measured compound action potentials (CAPs) in acutely deafened guinea pigs to further study the optoacoustic e®ect. 19 Widening the pulse duration from nanosecond to millisecond, Kallweit et al measured the pressure evoked by pulsed laser stimulating a water cylinder and the corresponding signal shapes of laser absorption in intracochlear optical stimulation of guinea pigs.…”