Convergence, inhibition, and disinhibition in somatosensory circuits of the Drosophila larva

Summary

Date: 
October 28, 2015 - 1:00pm
Location: 
NW 243
About the Speaker
Name: 
Casey Schneider-Mizell (Janelia)

Somatosensation is vital to understand ones immediate environment, seek comfort and avoid bodily harm. While diverse types of somatosensory neurons are well-mapped at the periphery across many species, the central circuits linking somatosensory information to behavior remain poorly understood. I will talk about the circuitry underlying two behaviors in the Drosophila larva: a vigorous escape and a less vigorous response to air currents. We identified a common core circuit involved in both behavioral responses using a combination of large-scale electron microscopy (EM) reconstructions, genetic techniques, electrophysiology and quantitative behavior. In the context of vigorous escape, we found a population of novel interneurons — which we named Basin cells — to be the first point of sensory convergence between nociception and mechanoception, both of which modulate rolling. Through EM reconstructions, we identified further loci of multimodal convergence on pathways between Basin cells and a command neuron for rolling, suggesting that multisensory integration is a distributed phenomenon, not occurring at any single point in the nervous system. In the context of air currents, we found that subtypes of Basin cells differentially modulate components of the behavioral response. Through EM reconstruction, we identified a complex network of inhibitory and disinhibitory circuitry well-posed for controlling Basin activity. We propose that a motif for feedback disinhibition is the key for this circuit to transition from a generic startle to a response specific to the details of the stimulus. Taken together, these results show how behavioral responses arise from the orchestration of parallel excitatory pathways by inhibitory and disinhibitory circuitry.