The expression of light-gated ion channels in a specific cell type through promoter control allows for the regulation of cell potential by either depolarizing the membrane to 0 mV for cation-permeant channelrhodopsin or by holding the voltage at –67 mV for anion-conducting channelrhodopsin. Depolarization can conduct a current in the range of 5 fA per channel and occurs on the timescale of action potentials and neurotransmitter exocytosis. They have an advantage over other types of ion channel regulation in that they provide non-invasive, reversible membrane potential changes with fine temporal and spatial control granted by induction through laser stimuli. They reliably stimulate single action potentials with rapid depolarization and can be utilized "in vivo" because they do not require high intensity illumination to maintain function, unlike other techniques like light-activated proton pumps and photoactivatable probes.