An optic fiber (0.2 mm core diameter) driven by a blue LED (470 nm, Doric Lenses) was placed ~0.5 mm above the exposed SC to photostimulate ChR2-expressing cells. The intensity of LED light was ~160 mW/mm2 at the tip of the optic fiber in all recordings, which was confirmed to be reliably effective in activating ChR2-expressing neurons (Shi et al., 2017 (link)).
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