"In the last few years, scientists have developed a way to stimulate neurons using light rather than electricity. Researchers first introduce a gene for a light-sensitive molecule, called channelrhodopsin 2 (ChR2), into a specific subset of neurons. Shining blue light on these neurons then causes them to fire. One advantage of this approach is its specificity--only the neurons with the gene are activated. It also provides a way to shut neurons off--introducing a different molecule, halorhodopsin (NpHR), silences the cells in response to yellow light. "That's the other unique thing about this approach," says Tim Denison, senior IC engineering manager in Medtronic's neuromodulation division. "It allows us to silence neurons' activity, which is extraordinarily difficult with electrostimulation."" - τorƍue