Circuit principles of behavioral choice in Drosophila


November 24, 2015 - 12:00pm
NW 243
About the Speaker
Marta Zlatic (Janelia)

A single nervous system can generate many distinct behaviors. Choosing which behavior to generate, based on sensory inputs, previous experience and internal state is crucial for the survival of any organism. I will talk about our efforts to map the structure of circuits involved in behavioral choice and to relate this structure to function. We use the genetically tractable insect model system, the Drosophila larva, with a 10,000-neuron nervous system and uniquely identifiable neurons - in which we can combine three levels of analysis: i) neural manipulation in freely behaving animals to determine causal relationship between neural activation and actions, ii) physiological measurements of neural activity during sensory integration and action selection and iii) circuit mapping using electron microscopy (EM).

I will talk about two specific questions that we are tackling by combining the three levels of analysis mentioned above: 1) how is information from multiple modalities integrated to guide behavioral choices; 2) how are memories used to guide behavioral choices.

1) Natural events present multiple types of sensory cues, each detected by a specialized sensory modality. Combining information from multiple modalities is therefore essential for the selection of appropriate actions. We have shown that combining mechanosensory and nociceptive cues synergistically enhances the selection of the fastest mode of escape locomotion in Drosophila larvae. In an electron microscopy volume that spans the entire insect nervous system we have mapped the multisensory circuit involved in the selection of distinct escape modes (rolling or crawling) comprising hundreds of neurons and spanning multiple levels of the sensory processing hierarchy, from sensory neurons to command-like neurons. Using behavioral and physiological studies we identified functionally connected circuit nodes that trigger the fastest locomotor mode, and others that facilitate it. The wiring diagram revealed a complex multilevel multimodal feedforward convergence architecture as well as a rich repertoire of inhibitory and disinhibitory feedback motifs. I will discuss our recent findings on the role of disinhibition neurons in multisensory integration.

2) We have shown that after several pairings of an odor with escape-evoking stimuli Drosophila larvae start avoiding the conditioned odor. To study the selection of conditioned odor escape responses we are mapping a circuit for aversive olfactory conditioning from the conditioned and unconditioned sensory inputs to the known center for olfactory conditioning in insects, the mushroom body, and from the mushroom body to motor outputs. This provides a framework to tackle several fundamental questions. How are memories formed, stored and recalled? How do learned associations modulate sensorimotor pathways to mediate the selection of conditioned responses? Understanding how memories and learned behaviors are encoded throughout the larval nervous system may provide direct insight into these processes in the larger insect and vertebrate nervous systems.