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When not running around outdoors, Dan develops and applies approaches to characterize the computational units of the brain. A physicist by training, Dan prefers to work on the tractable (yet still surprisingly complicated) fruit fly. The central brain of the fruit fly has 100,000 neurons. Thanks to recent efforts to image each of these neurons at high resolution with electron microscopy, the connectivity between each of them can now be found. Dan uses these neural connectivity maps to define computational units and then generates hypotheses about how the structure of these units leads to their individual functions. He then tests these hypotheses with the powerful set of genetic tools that are unique to the fruit fly. Almost every neuron in the fruit fly brain can consistently be identified across animals, and that neuron’s neural activity can be monitored, excited, or inhibited.
Dan has applied this approach to the fly’s head direction system, which is similar to the head direction systems found in mammals, birds, and fish. While head direction systems had previously been studied at a high level, Dan was able to use connectivity data to identify all of the neurons involved in the fly head direction system and to posit functional roles for each of them. He found that while the fly head direction system is largely consistent with longstanding theoretical models (which were developed for the mammalian system), it also features many additional, unpredicted elements. He is currently working to describe the functional role of these elements and hopes that the principles that he discovers will inform our understanding across species, not just of head direction systems but also of how the brain stores and updates internal representations of the world.