If anyone is wondering, the lasers aren't an essential element of what's going on here; the point is that targeted electrical stimulation to a certain area of the brain causes this behaviour. With areas on the brain surface, you could just use a wire for this.
For areas deeper in the brain, however, you can't exactly feed a wire in there without destroying things, so instead, you use optogenetics: you get a virus to be the "end" of the wire (finding the right area of the brain to live in, and then converting light pulses into electrical pulses) and then you point a laser at the brain and the viruses "go off" in response. The virus is essentially just serving as one half of an electrical optoisolator.
As an added benefit for the optogenetic approach, the electrical pulses released by the viruses are each local to their host cells, so they won't have nearly as much "bleed-over" into surrounding tissue as you'd see with one strong pulse from a wire.
For areas deeper in the brain, however, you can't exactly feed a wire in there without destroying things, so instead, you use optogenetics: you get a virus to be the "end" of the wire (finding the right area of the brain to live in, and then converting light pulses into electrical pulses) and then you point a laser at the brain and the viruses "go off" in response. The virus is essentially just serving as one half of an electrical optoisolator.
As an added benefit for the optogenetic approach, the electrical pulses released by the viruses are each local to their host cells, so they won't have nearly as much "bleed-over" into surrounding tissue as you'd see with one strong pulse from a wire.