2D surface maps of light distribution and temperature increase were recorded in wild type anesthetized rats brains during 90s light stimulation at 478nm (blue) and 638nm (red) with continuous or pulsed optical stimulations with corresponding power ranging from 100 up to 1200 mW/mm² at the output of an optical fiber. Post mortem maps were recorded in the same animals to assess the cooling effect of blood flow. Post mortem histological analysis were carried out to assess whether high power light stimulations had phototoxic effects or could trigger non physiological functional activation. Temperature increase remains below physiological changes (0,5 -1°) for stimulations up to 400mW/mm² at 40Hz. . Histology did not show significant irreversible modifications or damage to the tissues. The spatial profile of light distribution and heat were correlated and demonstrate as expected a rapid attenuation with diatnce to the fiber.
Suhan Senova, Ilona Scisniak, Chih Chieh Chiang, Isabelle Doignon, Claire Martin, Stephane Palfi, Antoine Chaillet, and Frederic Pain, "Experimental assessment of thermal effects of high power density light stimulation for optogenetics control of deep brain structures
(Conference Presentation)," Proc. SPIE 9690, Clinical and Translational Neurophotonics; Neural Imaging and Sensing; and Optogenetics and Optical Manipulation, 96902H (Presented at SPIE BiOS: February 14, 2016; Published: 26 April 2016); https://doi.org/10.1117/12.2210944.4848636590001.
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