INVESTIGATION OF A MULTI-SENSORY CIRCUIT FOR REJECTION BEHAVIOR IN DROSOPHILA FEMALES

Abstract

Understanding how the brain combines information from different sensory modalities to select appropriate behavioral actions remains a central challenge in neuroscience. While work in many systems has made substantial progress in understanding sensory processing in individual modalities, often working inward from the periphery, these studies have not investigated how information from different modalities are combined at the level of cells and circuits of the brain, to influence social behavior. The highly stereotyped architecture and compact form of the fruit fly brain, combined with its powerful genetic tools, make this model system uniquely suited to addressing this central challenge. This dissertation uses a mix of connectomics, machine learning technology for position tracking of natural behavior, genetic circuit manipulations, and two-photon calcium imaging, to investigate mechanisms underlying multisensory integration in Drosophila melanogaster. We identify nodes where auditory and visual pathways converge at synaptic resolution, at neurons known to drive a female rejection behavior, ovipositor extrusion (OE). We find that these multimodal neurons form a multilevel circuit, with each node poised to play a distinct role in modulating behavior. We describe how audiovisual cues from the male influence female OE, and show that some features of male-female communication are governed by either audition or vision, while other features are governed by a combination of the two modalities. We further manipulate key neurons in the circuit, to determine their contributions to OE behavior. This study elucidates how multisensory signals may converge at the cellular and circuit levels to influence a social behavior. Additionally, I explore state-dependent modulations of OE behavior, and investigate synaptic locations and properties of one case study cell of the underlying circuit. Taken together, this dissertation expands our understanding of how cells and circuits process multisensory signals and transform them into dynamic motor responses, in ethologically relevant settings.