Towards Safe Infrared Nerve Stimulation: A Systematic Experimental Approach

Neural activation by infrared nerve stimulation (INS) gains growing interest as a potential alternative to conventional electric nerve stimulation, since unambiguous advantages like contact-free operation, enhanced spatial selectivity and lack of (electrical) stimulation artifacts are promising for both future electrophysiological research and clinical application. For the systematic investigation of laser nerve activation, we recently introduced a novel experimental approach. Comprising a defined focused beam profile, it enables remote controlled, contact-free pulsed laser stimulation of the rat sciatic nerve, simultaneous to high-speed temperature measurement in vivo. Up to now, successful neural activation with single laser pulses (2 - 6 mJ) was observed in all performed experiments, however, it strongly depended on the particular nerve location. Hence, we depict the investigation of spatial dependency of the nerve response and identify 'regions of excitability' on the nerve surface, that are highly susceptible to INS. By means of thermal imaging, we simultaneously monitored the nerve surface temperature, where we observed progressing temperature build-up during single pulse stimulation with repetition rates above 4 Hz. In this work, we present current results of our ongoing research.