Project Summary A goal of many neurobiologists is to understand how the activity of cells and circuits in the brain relate to behavior, learning, and disease symptoms. Prior to optogenetics, it was nearly impossible to establish the sufficiency and necessity of activity in specific cells to the generation or modification of a behavior. Optogenetics refers to a rapidly progressing set of tools that allow researchers to use light to read out and manipulate the activity of genetically defined brain cells. With optogenetics, it is now possible to use light to monitor the activity of cells during behavior and then add or subtract activity from these cells to establish the causal relationship between it and behavior. Although optogenetics is nearly universally used, the proper design and interpretation of optogenetics-based experiments is still challenging. The goal of the 2022 Gordon Research Conference and Gordon Research Seminar on “Optogenetic Approaches to Understanding Neural Circuits and Behavior” meeting is to gather scientists from different disciplines and backgrounds who can collectively present best methods for use of optogenetic tools and recent discoveries made with optogenetics to a diverse group of scientists interested in uncovering the relationship between circuit activity and behavior. We will bring together experts who are providing new innovations in optogenetic approaches, such as new sensors, effectors, and microscopes, with scientists using these approaches to discover the neural underpinnings of behavior. Our hope is through the multiple opportunities provided (i.e., oral presentations, interactive poster sessions, community meals and free-time) both senior and junior scientists (i.e., trainees and junior faculty) will be able to build connections and learn from each other.We request funds to help offset the cost of travel, accommodation and registration for speakers and participants to attend this meeting.