LC4
systemVisionspeciesD. melanogaster3D view25 of 626 cellssources5
LC4 is a lobula columnar visual projection neuron type of the fruit fly that responds to looming, the rapid expansion of an approaching object’s image. LC4 neurons synapse directly onto the giant fiber escape neuron and convey how fast the object expands.
| Also known as | Lobula columnar type 4 · ColA (in larger flies) |
|---|---|
| Region | Lobula; axons end in the LC4 optic glomerulus, where they meet the giant fiber |
| System | Vision: eye and optic lobe |
| In the display bundle | 25 of the 626 reconstructed neurons in the site’s MaleCNS display bundle, which shows 626 of the model’s 166,700 neurons: LC4 25 |
Where they sit
LC4 dendrites lie in the lobula and their axons converge in the LC4 optic glomerulus, which is innervated by the giant fiber, designated DNp01 (Namiki et al., 2018).
What they do
Removing this input to the giant fiber during looming stimuli showed that it encodes the angular expansion velocity of the approaching object, while other inputs encode its angular size; the giant fiber integrates the two features linearly (von Reyn et al., 2017). The size component comes from LPLC2, and electron microscopy shows that both LC4 and LPLC2 synapse directly onto the giant fiber (Ache et al., 2019).
LC4 neurons viewing different parts of the visual field make opposite, graded numbers of synapses onto two descending neurons, DNp02 and DNp11, along the front-to-back axis of visual space. Activating DNp11 makes flies lean forward and DNp02 promotes backward takeoffs, so the location of a threat is converted into the direction of escape (Dombrovski et al., 2023).
Behavior
Optogenetic activation of LC4 drives jumping (Wu et al., 2016). Fast looms bias the fly toward rapid, giant-fiber-mediated escapes (von Reyn et al., 2017).