Outlook and approach:
We use olfactory navigation in Drosophila to understand the relationship between dynamics at the synaptic, circuit, and behavioral levels. Drosophila have relatively simple brains but exhibit complex behavior, making them ideal subjects for experiments linking synaptic biophysics to behavior. We are currently pursuing two projects, both characterized by a tight interaction between experiments and modeling:
Deciding on the wing:
Odors in air form turbulent plumes in which the local odor concentration can fluctuate rapidly as a function of time. Numerous behavioral studies have suggested that— due to the unpredictable dynamics of natural odors, insects navigate towards the source of an odor plume by combining odor information with mechanosensory or visual cues about wind direction. Our lab is interested in several questions related to this behavior. For example: How do wind-guided turns depend on the history of odor encounters? How do local behavioral algorithms depend on global statistical properties of odor and wind fluctuations? Which neurons integrate odor information with wind and visual cues? How does integration of sensory cues in individual neurons compare to behavioral integration of sensory cues by whole flies? We are addressing these questions using behavioral experiments and recordings from candidate neurons.
Synaptic biophysics and sensory coding:
Chemical synapses exhibit dynamics on the time scale of tens of milliseconds to seconds that are collectively known as “short-term plasticity”. Multiple mechanisms are thought to underlie these processes, such as accumulation of pre-synaptic calcium, pooling of neurotransmitter, depletion of synaptic veiscles, and inactivation of post-synaptic receptors. Different forms of short-term plasticity are characteristic of particular synapses, and theorists have long appreciated that these processes have important consequences for how time-varying signals are transmitted across a synapse. However, few experimental models allow for a direct comparison between the biophysical processes occurring at synapses and the in vivo responses of neurons to naturalistic stimuli. We are using the Drosophila olfactory system as a model for understanding the relationship between synaptic processes and encoding of time-varying stimuli by neural circuits. We are interested in questions such as: which steps in synaptic transmission most strongly determine the temporal coding properties of downstream neurons? How do changes in synaptic properties affect temporal coding in post-synaptic cells? How are synaptic properties modified dynamically by circuit feedback and behavioral state? What role do cell-type specific forms of synaptic short-term plasticity play in an integrated neural circuit? We are addressing these questions using a combination of high-temporal resolution imaging, electrophysiology, and pharmacological and genetic manipulations.