The study of innate behaviors is a central tenant of behavioral science and has a rich experimental provenance traced back to classic naturalist observational studies in the early and mid-twentieth century. The authors leverage published knowledge of a subset of neurons previously identified through genetic markers and thought to describe the potential for a complete innate behavior, and utilize an array of modern optical microscopy techniques to provide a functional and anatomical description of the neural circuits responsible for the expression of male courtship in Drosophila.
In a series of elegant experiments utilizing a behavioral assay in conjunction with in vivo 2 photon imaging they demonstrate functional activation of sexualy dimorphic P1 interneurons that correlates with behavioral expression that is ethologically appropriate with respect to presented stimuli (male and female Drosophila of different strains).
Using in vivo photoactivation techniques utilizing channelrhodopsin expression in P1 neurons, they demonstrate that optical activation of P1 neurons results in long lasting release of the expression of behavior related to male courtship in Drosophila.
In a series of in vitro experiments the authors utilize functional 2 photon imaging, 3-D anatomical mapping using 2 photon imaging, photoactivatable fluorescent proteins and 2 photon ablation to functionally and anatomically map the gustatory and olfactory sensory afferents that connect to P1 neurons.
In their conclusion, the authors present an anatomical and functional model showing how feedforward excitatory and inhibitory signaling can interact with P1 neurons to release a behavioral response that is appropriate to external species specific stimuli. In addition to describing the neural basis of a particular innate behavior, their model suggests a general cirguit mechanism for release of innate behaviors in response to appropriate stimuli. Personally I found this paper to be a fun read, as an undergraduate course in Animal Behavior many years ago initiated my own interest in studying the nervous system