Lighting Up Neurons Optogenetics allows precise temporal control of cell firing and is rapidly reversible. Specific wavelengths activate light-sensitive proteins expressed in neurons. At bottom left, when blue light illuminates a cell in which ChR2 has been incorporated, its firing rate increases dramatically. At right, when green-yellow light illuminates a cell in which NpHR is incorporated, its firing rate decreases dramatically. See more at https://www.youtube.com/watch?v=I64X7vHSHOE.