Lamina monopolar cells L1–L5
systemVisionspeciesD. melanogaster3D view82 of 626 cellssources5
Lamina monopolar cells L1 to L5 are the output neurons of the lamina, the first neuropil of the fruit fly’s optic lobe. They relay photoreceptor signals to the medulla, where L1 and L2 begin the ON and OFF pathways for motion vision.
| Also known as | L1 · L2 · L3 · L4 · L5 · Lamina neurons |
|---|---|
| Region | Lamina (optic lobe); axons end in the medulla |
| System | Vision: eye and optic lobe |
| In the display bundle | 82 of the 626 reconstructed neurons in the site’s MaleCNS display bundle, which shows 626 of the model’s 166,700 neurons: L1 24, L2 25, L3 22, L4 5, L5 6 |
What they are
The lamina is built from repeating modules called cartridges, one for each point in the visual field. A complete electron-microscopy reconstruction of a cartridge identified 12 neuron types: the R1–R6 photoreceptor terminals, the R7 and R8 fibres, the five monopolar cells L1–L5, the medulla neurons C2, C3 and T1, and a wide-field amacrine cell (Meinertzhagen and O'Neil, 1991).
Where they sit
L1–L5 have their branches in the lamina and send their axons to the medulla. At the lamina, the R1–R6 signal splits into four parallel pathways: L1, L2, L3 and the amacrine cell–T1 pathway (Rister et al., 2007).
What they do
Blocking L1 eliminates the responses of motion-sensitive neurons to moving bright edges, and blocking L2 eliminates responses to moving dark edges. Photoreceptor signals therefore segregate into an ON channel beginning with L1 and an OFF channel beginning with L2, much like ON and OFF bipolar cells in the vertebrate retina (Joesch et al., 2010).
L3 was first linked to orientation behavior rather than motion (Rister et al., 2007) and was later shown to act together with L1 and L2 as an input to motion-detecting circuits (Silies et al., 2013). A screen of all 12 lamina neuron classes found that L2 and L4, together with the feedback neurons C2 and C3, are required for normal detection of directional motion, and that nearly all lamina classes contribute (Tuthill et al., 2013).
Behavior
At high pattern contrast, the L1 and L2 pathways are redundant for motion-guided behavior; at intermediate contrast, L2 mediates front-to-back and L1 back-to-front motion (Rister et al., 2007).