RESUMO
A model of infrared neural stimulation (INS) has been developed to allow the temporal characteristics of different stimulation parameters and geometries to be better understood. The model uses a finite element approach to solve the heat equation and allow detailed analysis of heat during INS with both microsecond and millisecond laser pulses. When compared with experimental data, the model provides insight into the mechanisms behind INS. In particular, the analysis suggests that there may be two broad regimes of INS: the process tends to be limited by the total pulse energy for pulse lengths below 100 µs, while the temperature gradient with respect to time becomes more important above 100 µs.
Assuntos
Raios Infravermelhos , Modelos Neurológicos , Neurônios/fisiologia , Estimulação Física/métodos , Animais , Cóclea/efeitos da radiação , Simulação por Computador , Análise de Elementos Finitos , Gerbillinae , Temperatura Alta , Método de Monte Carlo , Temperatura , Condutividade TérmicaRESUMO
A Monte Carlo model has been developed to simulate light transport and absorption in neural tissue during infrared neural stimulation (INS). A range of fiber core sizes and numerical apertures are compared illustrating the advantages of using simulations when designing a light delivery system. A range of wavelengths, commonly used for INS, are also compared for stimulation of nerves in the cochlea, in terms of both the energy absorbed and the change in temperature due to a laser pulse. Modeling suggests that a fiber with core diameter of 200 µm and NA=0.22 is optimal for optical stimulation in the geometry used and that temperature rises in the spiral ganglion neurons are as low as 0.1°C. The results show a need for more careful experimentation to allow different proposed mechanisms of INS to be distinguished.