| dc.description.abstract | Infrared neural stimulation (INS) is a label-free method that uses infrared light to excite neural tissue. INS has high spatial specificity and artifact-free stimulation, offering distinct benefits compared to traditional electrical stimulation methods. Although previous studies show that INS is strongly dependent on the spatial and temporal thermal gradients from the laser irradiation, the underlying mechanisms are not fully understood. One of the mechanistic effects that is particularly unknown is the photomechanical contribution. Using the Scalable Effects Simulation Environment (SESE) developed for the Air Force Research Laboratory, the photoacoustic effects from a laser irradiating a single nerve were modeled using optical, thermal, and mechanical properties. SESE uses a Monte Carlo approach to calculate the radiative energy distribution of the laser irradiation that is then fed into the heat equation before linear elastic equations with a thermal expansion term are solved to obtain the photomechanical effects over space and time. The SESE mechanical model is validated against previous surface displacement measurements of rat sciatic nerve and initial pressure measurements in polyacrylamide gel. The resulting temperature, displacement, and pressure are compared across different pulse structures, allowing for insight of the sensitivity of the photomechanical effects from laser irradiation. There are higher magnitude mechanical effects, namely pressure and displacement changes, during shorter pulses or pulses with an initial energy spike. Higher magnitude pressure transients and larger displacement fluctuations also appear to correlate to lower stimulation thresholds. The data from this modeling study supports that shorter pulses result in more significant mechanical effects, specifically pressure and displacement changes, and thus supports the hypothesis that there is indeed a mechanical component to the INS mechanism. This insight will allow for finer tuning of the laser parameters needed for INS to move towards clinical applications. | |
