Effects of heat conduction on the spatial selectivity of infrared stimulation in the cochlea

BACKGROUND: It has been reported that one of the main mechanisms that induces the activation of the cochlea through infrared laser light is the photothermal effect. The temperature in the spiral ganglion cells increases as a result of photon absorption. However, heat conduction can induce an increase in the temperature within the cochlea and change the spatial selectivity of activation. METHODS: We analyzed the effects of heat conduction on the increase in temperature within the cochlea using a 3D model that simplifies the spiraled cochlea as a rotational symmetric structure . The model is solved using the finite element method. RESULTS: Taken as an example, the cochlea is stimulated by laser pulses at eight sites in its first turn. The temperature rise in time domain and spatial domain is simulated for different laser pulse energies and repetition rates. The results demonstrate that the temperature in the cochlea increases as the laser pulse energy and repetition rate increase. Additionally, the zone affected by the laser is enlarged because of the heat conduction in the surrounding structures. As a result, more auditory neurons can be stimulated than the expected. CONCLUSIONS: The heat conduction affects the laser spatial selectivity however, by adjusting the stimulation schemes of the laser pulse-trains, such as laser repetition rate and laser power, the laser selectivity can be optimized.