CsChrimson is a light-gated cation channel that can be used as an optogenetic tool to activate neurons; it is optimally excited by light of 590nm wavelength. It is an artificial channelrhodopsin in which the extracellular N-terminus of the Chlamydomonas noctigama CnChR1 'Chrimson' gene has been replaced with the corresponding sequence from the Chloromonas subdivisa CsChR gene (FBrf0227011, FBrf0224260). The formation of a functional channel requires the presence of a covalently linked all-trans-retinal chromophore which can be provided exogenously if necessary via the culture medium or diet (this cofactor is present endogenously in some intact vertebrate systems). For detailed kinetic and spectral properties, see FBrf0227011, FBrf0224260.