Research in this laboratory is aimed at understanding the neurobiology of emotion. We seek to elucidate how fundamental properties common to emotional states, such as persistence, scalability and valence, are encoded in the circuitry and chemistry of the brain and how these internal states combine with sensory stimuli to elicit specific emotional behaviors, such as fear or aggression. Our work employs optogenetics, chemogenetics, single-cell RNAseq and viral tracing to mark, map, and manipulate specific neural circuits to determine how genetically identifiable populations of neurons causally control internal emotion states and behavior. These studies are complemented by the use of electrophysiology and functional imaging to measure activity in neural circuits. We have used mice and the fruit fly Drosophila melanogaster as model organisms. More recently we have established a genetically tractable jellyfish model (Clytia hemisphaerica) with the goal of determining whether these ancient organisms without a brain behave in a purely reflexive manner, or also have primitive internal states.