T4 and T5 motion detectors
systemVisionspeciesD. melanogaster3D view60 of 626 cellssources5
T4 and T5 are the first direction-selective neurons in the fruit fly’s visual system. T4 cells respond to moving bright (ON) edges and T5 cells to moving dark (OFF) edges, and each of their four subtypes prefers one of the four cardinal directions.
| Also known as | T4a · T4b · T4c · T4d · T5a · T5b · T5c · T5d · Elementary motion detectors |
|---|---|
| Region | Medulla (T4) and lobula (T5); axons end in the lobula plate |
| System | Vision: eye and optic lobe |
| In the display bundle | 60 of the 626 reconstructed neurons in the site’s MaleCNS display bundle, which shows 626 of the model’s 166,700 neurons: T4a 20, T4b 1, T4c 2, T4d 3, T5a 24, T5b 1, T5c 3, T5d 6 |
What they are
Calcium imaging showed that subpopulations of T4 and T5 cells are each tuned to one of four directions: front-to-back, back-to-front, upward or downward. Depending on its preferred direction, each subtype terminates in its own layer of the lobula plate (Maisak et al., 2013). The subtypes are named a to d.
Where they sit
T4 dendrites lie in the medulla and T5 dendrites in the lobula; both send their axons to the four layers of the lobula plate (Maisak et al., 2013; Shinomiya et al., 2019).
What they do
Blocking T4 output selectively impairs the responses of downstream lobula plate neurons to moving ON edges, and blocking T5 impairs responses to OFF edges (Maisak et al., 2013). Direction selectivity is computed within the T4 dendrites from inputs that are not themselves direction-selective (Strother et al., 2017), and the connections onto these cells are consistent with their preferred directions (Takemura et al., 2013).
Their outputs feed large, wide-field motion-sensitive neurons of the lobula plate (Maisak et al., 2013) and lobula plate projection neurons such as LPLC2, whose cross-shaped dendrites collect outward motion from all four T4/T5 layers to detect looming (Klapoetke et al., 2017).
Behavior
Blocking T4 or T5 selectively compromises the turning responses of tethered walking flies to moving ON or OFF edges (Maisak et al., 2013).