Nature Reviews Neuroscience 8, 577–581 (2007)

On page 577, for clarity the references 53 and 54 have now been included. The wording of the first sentence of the second paragraph in the section 'Optogenetics: two microbial opsins' has also slightly changed for clarity, and should therefore read:

ChR2 (initially cloned in REFS 53,54) is a cation channel that allows sodium ions to enter the cell following exposure to 470 nm blue light23, whereas NpHR is a chloride pump24 that activates upon illumination with 580 nm yellow light (FIG. 1a).