Figure 1.

Genetically encoded, targetable actuator and reporter proteins that allow the use of light to either control or report molecular processes in specific cell populations within networks of heterologous cell types. a, Optical reporting and control are exemplified respectively by a voltage-sensitive fluorescent protein (VSFP2, left) and a light-sensitive ion channel (ChR2, top right) or ion pump [Np-halorhodopsin (NpHR), bottom right] that are directly gated by photoabsorption. Membrane potential traces are schematically indicated in red. VSFP2 reports action potential firing via an optical signal (green trace), while light is used to induce (ChR2) or inhibit (NpHR) action potential generation via the activity of actuator proteins. b, Optogenetic reporters and actuators can be selectively expressed in specific sets of neurons using genetic techniques. c, Light may be delivered (and collected) either by simple epi-illumination optics or more precisely targeted configurations, such as via fiber optics. Combinations of both methods can be used to investigate causality between the activity of specific neuronal populations and behavior.