Optoacoustic effect is responsible for laser-induced cochlear responses

Abstract

Optical stimulation of the cochlea with laser light has been suggested as an alternative to conventional treatment of sensorineural hearing loss with cochlear implants. The underlying mechanisms are controversially discussed: The stimulation can either be based on a direct excitation of neurons, or it is a result of an optoacoustic pressure wave acting on the basilar membrane. Animal studies comparing the intra-cochlear optical stimulation of hearing and deafened guinea pigs have indicated that the stimulation requires intact hair cells. Therefore, optoacoustic stimulation seems to be the underlying mechanism. The present study investigates optoacoustic characteristics using pulsed laser stimulation for in vivo experiments on hearing guinea pigs and pressure measurements in water. As a result, in vivo as well as pressure measurements showed corresponding signal shapes. The amplitude of the signal for both measurements depended on the absorption coefficient and on the maximum of the first time-derivative of laser pulse power (velocity of heat deposition). In conclusion, the pressure measurements directly demonstrated that laser light generates acoustic waves, with amplitudes suitable for stimulating the (partially) intact cochlea. These findings corroborate optoacoustic as the basic mechanism of optical intra-cochlear stimulation.

Infrared neural stimulation induces intracellular Ca2+ release mediated by phospholipase C

“…Thus, we investigated whether we observed similar Ca 2+ responses with shorter pulses in the thermal confinement regime. This condition is when the duration of the IR exposures t p respects the relationship, t p ≤ δ 2 /4 κ , where δ is the smallest dimension of heated volume and κ is the thermal diffusivity of water, κ ≈ 1.3 × 10 −3 cm 2 /s. With our setup, the smallest dimension of the heated volume was the fiber core radius.…”

Ryanodine and IP3 receptor-mediated calcium signaling play a pivotal role in neurological infrared laser modulation

“…[1][2][3][4][5][6][7][8] Likewise, ∼1.8 μm IR pulse exposure has also been demonstrated to block action potential (AP) generation and propagation. [9][10][11][12][13] While a rapid increase in temperature, due to absorption of the laser radiation, is required to evoke the neural depolarization, and IR stimulation pulses have been shown to produce an acoustic pressure wave, 14-17 the mechanism(s) to stimulate or inhibit an AP is not fully understood. 18 Certain thermal and mechanical mechanisms 17,19 involving ion channels, such as transient receptor potential (TRP) channel activation, 20 plasma membrane poration, 21 and/or membrane potential changes, are suggested as explanations for IR neural stimulation and inhibition, together termed IR neural modulation (INM).…”

Photoacoustic effect invokes auditory response in infrared neuron stimulation

“…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. They proposed an optoacoustic e®ect as the basic mechanism of INS.…”