One of the biggest challenges of brain research is how to single out the contribution of a specific neuron types to brain functions and brain disorder states in this ultra-complex network [3], [4]. Ten years ago, a technique called optogenetics was developed, which combines lasers, fiber optics, and genes for light-responsive protein channels called microbial opsins from algae and bacteria to control neural activity precisely in specific nerve cells within whole living brains as animals carry out their daily activities [3].

Briefly, a natural light-sensitive ion-transporting membrane protein (e.g., channelrhodopsin (ChRs), chloride-conducting ChRs (ChloCs)) is expressed in neurons of choice. Shining light to the cells will open the ion channels to generate electrical signals to either stimulate or inhibit neuronal activities. Since the first demonstration of this approach in cell cultures, optogenetics has become the method of choice in neuroscience, which has been successfully applied in many animal models including Caenorhabditis elegans, Drosophila melanogaster, zebrafish, mice, and nonhuman primates [3], [4].