Optogenetics was motivated by the recognition that light may be an ideal stimulus for the orthogonal control of cell and animal behavior: light can be applied and withdrawn remotely and with ease given a sufficiently transparent matrix, and light permits transient and local activation on very short time and length scales (down to or below milliseconds and micrometers, respectively). Optogenetics flourished in the hands of neurobiologists, and ion conducting microbial opsins have been repurposed to decode neural circuits in behaving animals during the last decade