Multiplexing optogenetic manipulation and readout requires using the whole optical spectrum. So far, red-shifted genetically encoded voltage indicators have suffered from low sensitivity that limited in vivo use. In a recent paper in Nature Methods, Pieribone and colleagues present VARNAM, a FRET-opsin indicator that is imageable under moderate intensities. The authors show that VARNAM can image action potentials in cell cultures, brain slices and live Drosophila and cortical and hippocampal rhythms in freely behaving mice.

https://www.nature.com/articles/s41592-018-0188-7