Also, check out this lovely companion paper from @SungSoo_111: https://www.nature.com/articles/s41586-019-1767-1 …. And beautiful summary by @malcgcamp & @lisa_giocomo: https://www.nature.com/articles/d41586-019-03443-1 … 2/
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A network in the fly's brain contains E-PG neurons that are arranged physically in a ring and contain a bump of activity that tracks the fly’s heading like a compass. In the dark, the compass estimates heading using self-motion but visual cues make the estimate more accurate. 3/pic.twitter.com/oa9dq6hTup
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But how does this work when the visual surroundings change? A hint came from anatomy - a group of inhibitory visual neurons called R neurons each sends an axon that contacts every E-PG neuron in the compass network. 4/pic.twitter.com/iKQCVxZR2W
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This all-to-all connectivity is intriguing because if synapse strengths can change with experience then this network could flexibly learn the association between the *current* view of visual cues and heading direction. 5/
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When we performed whole-cell recordings from E-PG neurons, each cell was inhibited by some visual some regions and not others. Across flies, E-PG neurons had different visual tuning, suggesting that different visual-heading associations exist in different flies. 6/pic.twitter.com/UIrW2tBABV
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Silencing R neurons using Kir2.1 reduced this visual inhibition, supporting the idea that R neurons provide this inhibitory visual drive. We think this visual drive normally keeps the compass accurate and “in sync” with visual cues in the surrounding. 7/pic.twitter.com/GbhfsssfUQ
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This leads to an important question: Does visual drive to the compass change when the fly’s visual experience changes? To test this, first, we used calcium imaging with virtual reality (VR) and switched the fly between VR w/ 1-cue or 2-cues spaced symmetrically. 8/
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As expected, in the symmetric VR, the compass toggled between two representations (offsets). Interestingly, upon returning the fly to the 1-cue VR, we often saw the compass continue to toggle, arguing that the 2-cue VR experience left a persistent imprint on the network! 9/pic.twitter.com/vTlVKcuCvI
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Using electrophysiology, we found that visual drive also reorganizes when the fly explored a new environment. Interestingly, we only saw visual changes in cells with large changes in activity during 2-cue training, so remapping likely requires E-PG activity. 10/pic.twitter.com/OG4CyVMMRU
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We think that synapses between R neurons & E-PGs reorganize by associative plasticity to store the current surroundings. Theory has proposed how plasticity can allow a network to learn during exploration. We found evidence for such plasticity in the brains of exploring flies! 11/pic.twitter.com/Uv80PWXk4v
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