Real-time multimodal optical control of neurons and muscles in freely-behaving Caenorhabditis elegans

The ability to optically excite or silence specific cells using optogenetics has provided a powerful tool to interrogate the nervous system. Optogenetic experiments in small organisms have mostly been performed using whole-field illumination and genetic targeting, but these strategies do not always provide adequate cellular specificity. Targeted illumination can be a valuable alternative but to date it has only been shown in non-moving animals without the ability to observe behavior output. We present a real-time multimodal illumination technology that allows both tracking and recording the behavior of freely moving Caenorhabditis elegans while stimulating specific cells that express Channelrhodopsin-2 or MAC. We use this system to optically manipulate nodes within the C. elegans touch circuit and study the roles of sensory and command neurons and the ultimate behavioral output. This technology significantly enhances our ability to control, alter, observe, and investigate how neurons, muscles, and circuits ultimately produce behavior in animals using optogenetics.