Abstract
.Significance: Infrared neural stimulation (INS) utilizes pulsed infrared light to selectively elicit neural activity without exogenous compounds. Despite its versatility in a broad range of biomedical applications, no comprehensive comparison of factors pertaining to the efficacy and safety of INS such as wavelength, radiant exposure, and optical spot size exists in the literature.Aim: Here, we evaluate these parameters using three of the wavelengths commonly used for INS, 1450 nm, 1875 nm, and 2120 nm.Approach: In an in vivo rat sciatic nerve preparation, the stimulation threshold and transition rate to 100% activation probability were used to compare the effects of each parameter.Results: The pulsed diode lasers at 1450 nm and 1875 nm had a consistently higher () stimulation threshold than that of the Ho:YAG laser at 2120 nm (). In addition, the Ho:YAG produced a faster transition rate to 100% activation probability compared to the diode lasers. Our data suggest that the superior performance of the Ho:YAG is a result of the high-intensity microsecond spike at the onset of the pulse. Acute histological evaluation of diode irradiated nerves revealed a safe range of radiant exposures for stimulation.Conclusion: Together, our results identify measures to improve the safety, efficacy, and accessibility of INS technology for research and clinical applications.
Highlights
For the last century, scientists and clinicians have used the direct application of electrical current to modulate neural activity and probe the structure and function of the nervous system.[1,2,3,4] To this day, electrical stimulation remains the gold standard for assessing and quantifying neural activity
Electrical stimulation is hindered by fundamental limitations, namely, current spread and stimulation artifacts
The goal of this study is to identify optimal stimulation parameters across three short-wave infrared (SWIR) wavelength lasers, two diode lasers centered at 1450 nm and 1875 nm, and the “gold standard” Ho: YAG laser at 2120 nm, to empirically evaluate the efficacy and histological safety of these wavelengths in an in vivo rat sciatic nerve model
Summary
Scientists and clinicians have used the direct application of electrical current to modulate neural activity and probe the structure and function of the nervous system.[1,2,3,4] To this day, electrical stimulation remains the gold standard for assessing and quantifying neural activity. In which the injected current disperses into the surrounding tissue, restricts the spatial specificity of neural activation.[5,6] Spatial specificity is both clinically and experimentally advantageous when targeting specific regions of a nerve or other neural structures such as the brain and cochlea which have a high degree of spatial dependence.[7,8,9] Clinically, current spread in deep brain stimulation cases can cause deleterious side effects that may hinder the effective treatment of Parkinson’s disease.[10,11,12]
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