Interesting idea in this post at Labrigger:
Compared to visible (vis) light, near infrared (NIR) wavelength scatters less and is less absorbed in brain tissue. If your fluorescent target absorbs vis light, then one way to use NIR is to flood the area with molecules that will absorb NIR and emit vis light. The process is called “upconversion“, since it is in contrast to the more common process of higher energy (shorter wavelength) light being converted into lower energy (longer wavelength) light. The effect looks superficially similar to two-photon absorption, but it’s a very different physical process.
Apparently you can now do this with optogenetics, and is much higher wavelength than Chrimson or ReaChR. Reminds me a bit of Miesenbock’s Trp/P2X2 optogenetics system from 2003.
Also on Labrigger: open source intrinsic imaging
[Invertebrate note: since ReaChR allows Drosophila researchers to activate neurons in intact, freely behaving flies, perhaps this might give us a method to inactivate with Halorhodopsin?]