Fly motion vision: From optic flow to visual course control. [Das Bewegungssehen der Fliege: Vom optischen Fluss zur visuellen Kurskontrolle]

Optic flow-based navigation has been studied extensively in flies, both in tethered as well as in freely flying animals. As neural control elements, the tangential cells of the lobula plate seem to play a key role: they are sensitive to visual motion, have large receptive fields, and, with their spatial distribution of preferred directions, match the optic flow as elicited during certain types of flight maneuvers. However, the neural circuit presynaptic to the tangential cells responsible for extracting the direction of motion locally has long escaped investigation, due to the small size of the participating neurons. Recent progress was made here by combining genetic silencing of candidate neurons with whole-cell patch recording from tangential cells in Drosophila. This approach led to the identification of lamina neurons L1 and L2 providing the input signals to two parallel motion detection circuits, specialized for brightness increments (L1, ON-pathway) and decrements (L2, OFF-pathway), respectively