Pulsed 808-nm infrared laser stimulation of the auditory nerve in guinea pig cochlea

Abstract

Pulsed near-infrared radiation has been proposed as an alternative stimulus for auditory nerve stimulation and could be potentially used in the design of cochlear implant. Although the infrared with high absorption coefficient of water (i.e., wavelength ranged from 1.8 to 2.2 μm) has been widely investigated, the lymph in the cochlea absorbs most of the infrared energies, and only a small part can arrive at the target auditory nerves. The present study is aimed to test whether the short-wavelength near-infrared irradiation with lower absorption coefficients can penetrate the lymph fluid to stimulate the auditory nerves. An 808-nm near-infrared laser was chosen to stimulate the auditory nerve in the guinea pig cochlea. The infrared pulse was delivered by an optical fiber that was surgically inserted near the round window membrane and oriented toward the spiral ganglion cells in the basal turn of the cochlea. The 2-Hz infrared pulses were used to stimulate the cochlea before and after the deafness with different pulse durations (100-1,000 μs). Optically evoked compound action potentials (oCAPs) were recorded during the infrared radiation. We successfully recorded oCAPs from both normal hearing animals and deafened animals. The oCAP amplitude increased with the infrared radiation energy. The preliminary experiment suggests that the near-infrared with lower absorption coefficients can effectively pass through the lymph filled in the cochlea and stimulate the auditory nerve. Further studies will optimize the deafness animal model and determine the optimal stimulation parameters.

Auditory nerve impulses induced by 980 nm laser

“…The CAP amplitudes recorded in this study were larger than 808 μm at the same radiation exposure. 27 This result can be attributed to differences in pulse duration at fixed radiant exposure.…”

“…5 for 1.94 μm wavelength. 19 As for the 808 nm wavelength 27 in Fig. 4 and for the 1.94 μm wavelength 19 in Fig.…”

“…26 However, to the best of our knowledge, studies using these wavelengths are few in number, comprising only a handful of experiments at the 808 nm wavelength. 27 There is also insufficient information on laser parameters. Therefore, we chose the wavelength of 980 nm which has not been previously explored for use in optical stimulation of the auditory nerve for our study.…”

Attenuated infrared neuron stimulation response in cochlea of deaf animals may associate with the degeneration of spiral ganglion neurons

“…Compared to electrical stimulation, optical stimulation of the cochlea has attracted attention due to its high spatial precision, superior resolution, non-overlapping stimulation, with few stimulation artifacts or electrochemical interactions between the stimulation source and the tissue [2,3,20]. Previous studies on infrared laser auditory stimulation focused on cochlear functions by recording CAPs [3,8,11,14,21,22], and only a few studies measured oABRs evoked by optical stimulation in normal hearing animals [15,23]. The present study demonstrates that infrared laser pulses with wavelengths of 1850 nm could stimulate SGNs to evoke stable oABRs in both normal hearing and deafened guinea pigs.…”

In vivo auditory nerve stimulation with visible light

“…[22][23][24] The OCAP latency induced by 465-nm light was $2.0 ms, compared to > 1:7 ms for OCAPs induced by 980-nm light. 21 Latency is dened as the time necessary for information to disseminate in a cytodendritic structure consisting of a hair cell and a®erent nerve endings.…”