ChR2(H134R) is a light-gated cation channel that can be used as an optogenetic tool to activate neurons; the peak activation wavelength is approximately 470nm (PMID:21504945). It is an engineered derivative of ChR2, containing the H134R amino acid substitution, a gain of function mutation (PMID:16360690). 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 PMID:16360690, PMID:21504945 and PMID:22179551. For a comparison of ChR2(H134R) and other neuron activation tools, see PMID:20621963, PMID:21745635 and PMID:22179551.