Figure 1: Neural input adaptation and motion detection in the Drosophila OFF Pathway.

A. The temporal processing properties of sensory neurons, here represented by idealized temporal filters, have been shown to be stimulus and/or state dependent, varying in frequency, gain, and biphasic tuning (which can also affect frequency tuning). B. Filter shape can have a strong effect on the output of a motion detector. The linear combination of two excitatory inputs spatially offset by Δx°, one of which is biphasic (bottom, input 1 is monophasic, while input 2 is biphasic), can effectively suppress ND responses, generating an output that is more direction selective than the sum of two monophasic inputs (top). C. Schematic of the feed-forward Drosophila OFF motion pathway circuit Inset: T5 cells receive the majority of their input from columnar Tm1, Tm2, Tm4 and Tm9. Using the spatial distribution of synaptic inputs to T5 dendrites in the lobula, Shinomiya et al.⁹ infer the spatial structure of inputs in the medulla: Tm1/Tm2/Tm4 are postsynaptic to lamina monopolar cell L2 and look at the same point in space. They are spatially offset (Δx°) from Tm9, which is postsynaptic to L3. Voltage responses in T5 are direction selective, depolarizing more strongly to motion in the preferred direction (PD) than to motion in the opposite, null direction (ND). The mechanisms underlying the emergence of these signals in T5 are debated.