Let me know what you think.
The jist of it is that they can use a virus to implant genes in a small area of the brain, with markers to specify certain types of neurons, that essentially make the neurons into photodiodes--or rather, make them fire when exposed to light. And with fiber optics, you can target light very precisely, and use it to fix certain mental disorders (they focus on Parkinson's in particular).
It's really fascinating stuff. The future applications are also insane: another gene can be added on to make the neurons glow when they do something, and that light can be picked up by the fiber optics, which can be used for making feedback loops. Two way mental traffic.
I wouldn't be surprised to see this technology being used for straight up controlling machines in the future.