Infrared neural stimulation (INS) is a promising neuromodulation technique capable of exciting neural tissue without the need for exogeneous agents or genetic modification. Due to its high spatial specificity, INS could improve upon traditional methods of selective neural stimulation in both the laboratory and the clinic. As of yet, no study has compared the efficacy and safety of using different INS parameters such as spot size and wavelength. Moreover, differences in the methods of determining energy deposition and laser spot size make it difficult to compare stimulation parameters used in the current literature. Here, we present results comparing INS efficacy using 1450nm and 1875nm light over a range of spot sizes and radiant exposures. Stimulation thresholds were determined using recorded compound muscle action potentials (CMAPs) and visible muscle contractions in an in vivo rat sciatic nerve model. Overall, 1450nm light required lower radiant exposures to achieve threshold activation as compared to 1875nm. While radiant exposures remained relatively constant across different spot sizes when using 1450nm, the threshold radiant exposures for 1875nm exposures increased with spot size suggesting deeper nerves fibers tend to be activated. Moreover, exposures using a flat-top beam profile yielded less variability in the stimulation threshold than those using a Gaussian profile. As in previous studies, histology confirmed that damaging radiant exposures are several times greater than the stimulation threshold for both 1450nm and 1875nm. Our results provide valuable insight for future studies involving INS and for further developing INS as both a research and clinical tool.
Graham Throckmorton, Wilson R. Adams, Zane Ricks, Jonathan Cayce, E. Duco Jansen, and Anita Mahadevan-Jansen, "Comparing the efficacy and safety of infrared neural stimulation at 1450 nm and 1875 nm (Conference Presentation)," Proc. SPIE 10866, Optogenetics and Optical Manipulation 2019, 108660G (Presented at SPIE BiOS: February 03, 2019; Published: 7 March 2019); https://doi.org/10.1117/12.2508055.6011368243001.
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