How do scientists control brain cells with lasers?
Neurons fire when electrically charged atoms – ions – flood in and out of them, creating a tiny electric potential across their membranes. In 2005, a team at Stanford University in California reported that light-sensitive microbial proteins that also move ions can cause the same changes when they are genetically engineered into neurons. One algal protein, channelrhodopsin-2, turns neurons on when bathed in blue light, while its foil, halorhodopsin, silences neurons under yellow light. If these proteins are already around, what’s new? Channelrhodopsin-2 works swimmingly: it recently helped identify a brain circuit that, when activated, may ease symptoms of Parkinson’s. However, halorhodopsin has fallen short of hopes. The protein fails to fully silence neurons and grows sluggish after repeated cycles of light, says Ed Boyden, a neuroscientist who worked on both proteins at Stanford with his colleague Karl Deisseroth: “It didn’t work very well and it hasn’t found much of an application.”
