"First, they infected the mice with a virus that made the neurons in their brains sensitive to blue light."
They can do this? This is amazing to me!
It also makes me a little afraid that I'll get infected by a virus and mind controlled.
They can do this? This is amazing to me!
It also makes me a little afraid that I'll get infected by a virus and mind controlled.
First, the virus isn't found in the wild--it's been modified to carry the gene coding for a light-sensitive protein (opsin). When the cells are infected, they start producing these proteins themselves. To do this, the virus is typically applied directly to the brain tissue.
Light causes these opsins to change shape, which then allows specific types of ions to flow through the cell (typically sodium to excite cells, chloride to suppress them). However, for this to work, the channels need to be illuminated directly, with the correct wavelength of light, so an optical fiber is implanted in or just above the brain.
If someone were to do this to you, you would have already had a pair of fairly invasive neurosurgeries, so being mind-controlled is probably the least of your worries! However, this technique only lets you activate all neurons or all neurons of a specific type within the light's path. It would be fairly hard to induce a complex behavior, unless there's a pre-existing circuit for one (as shown here, which is why this paper is so interesting) or they can find an illumination pattern to mimic one.
Is the blood/brain barrier the ultimate savior?
Rabies has the interesting ability to move trans-synaptically. Specifically, it moves "backwards" from a post-synaptic cell into its presynaptic partners. This makes it very useful for studies where you want to label or manipulate connections between areas. On the other hand, this would make it more difficult to study all cells or all cells of a specific type in one area.
Incidentally, I'm not sure if rabies crosses the blood-brain barrier per se. It moves up to the brain via peripheral nerves instead of circulating through the blood. In fact, the blood brain barrier may be a problem for rabies because it prevents immune cells from cleaning out the virus inside the central nervous system.
Be glad you're not an ant :)