In vivo auditory nerve stimulation with visible light

Abstract

Background: Infrared laser stimulation has been proposed as an innovative method to elicit an auditory nerve response. Most studies have focused on using long-wavelength infrared ([Formula: see text][Formula: see text]nm) pulsed lasers with high water absorption coefficients. This paper sought to assess whether a short-wavelength laser (465[Formula: see text]nm) with an absorption coefficient as low as 10[Formula: see text][Formula: see text]cm[Formula: see text] would activate the auditory nerve and studied its potential mechanism. Method: Optical compound action potentials (OCAPs) were recorded when synchronous trigger laser pulses stimulate the cochlea before and after deafening, varying the pulse durations (from 800[Formula: see text][Formula: see text]s to 3600[Formula: see text][Formula: see text]s) and the amount of radiant energy (from 18.05[Formula: see text]mJ/cm2 to 107.91[Formula: see text]mJ/cm2). A thermal infrared imager was applied to monitor the temperature change of the guinea pig cochlea. Results: The results showed that pulsed laser stimulation at 465[Formula: see text]nm could invoke OCAPs and had a similar waveform compared to the acoustical compound action potentials. The amplitude of OCAPs had a positive correlation with the increasing laser peak power, while the latency of OCAPs showed a negative correlation. The imager data showed that the temperature in the cochlea rose quickly by about 0.3[Formula: see text]C right after stimulating the cochlea and decreased quickly back to the initial temperature as the stimulation ended. Conclusions: This paper demonstrates that 465-nm laser stimulation can successfully induce OCAPs outside the cochlea, and that the amplitude and latency of the invoked OCAPs are highly affected by laser peak power. This paper proposes that a photothermal effect might be the main mechanism for the auditory nerve response induced by short-wavelength laser stimulation.