A, The halorhodopsin photocycle at high-power continuous illumination on the timescale of a typical photocycle (i.e. conditions used for neural silencing, > few ms). The HR410 intermediate is the origin of long-lived inactivation in neural silencing (e.g., (36, 75)). B, The photocycle of the H. salinarum bacteriorhodopsin. The photocycle has been simplified to reflect the dominant photocycle at large continuous illumination on the timescale of a typical photocycle (i.e. conditions used for neural silencing, > few ms). The M412 alternate intermediate is the origin of long-lived inactivation with bacteriorhodopsin. In contrast, Arch spontaneously quickly recovers from this state in the dark.