, 1998, Single and Borst, 1998 and Single et al., 1997). However, it is unclear if the computational nodes of the HR-EMD, the delay filter and the multiplier, correspond

to individual cell types, or if motion detection is computed in a more distributed manner, with distinct contributions from many different neurons. It is also possible that there are multiple circuits dedicated to motion computation; different neuron types could extract specific visual features, as in vertebrate retinal ganglion Selleckchem Ibrutinib cells (Gollisch and Meister, 2010), and compute motion independently within parallel channels. Indeed, several recent studies suggest that fly motion vision may be segregated into parallel, functionally distinct channels (Clark et al., 2011, Eichner et al., 2011, Joesch et al., 2010, Katsov and Clandinin, 2008 and Rister et al., 2007). The fly visual system consists of four ganglia NVP-BGJ398 supplier called the lamina, medulla, lobula, and lobula plate (Figure 1A), which together are referred to as the optic lobes. As the first

synaptic relay between the photoreceptors and motion-sensitive tangential neurons in the lobula plate, it has been hypothesized that the early stages of motion computation may occur in the lamina (Coombe et al., 1989 and Douglass and Strausfeld, 1995). The lamina is organized into an array of ∼750 retinotopic “cartridges,” each of which corresponds to a discrete sample of the visual world, ∼5° in Drosophila ( Braitenberg, Thalidomide 1967, Buchner, 1971 and Kirschfeld, 1967). The anatomy and connectivity of lamina neurons is known in exquisite detail, owing to detailed Golgi studies ( Fischbach and Dittrich, 1989) and electron microscopy (EM) reconstructions ( Meinertzhagen and O’Neil, 1991 and Rivera-Alba et al., 2011). Six light-sensitive photoreceptors, R1–R6, project their axons into each lamina cartridge. Two other photoreceptor neurons, R7 and R8, pass through the lamina and synapse in specific layers of the medulla. Besides

the photoreceptor axons, the lamina also contains processes of 12 other neuronal cell types (Figures 1C and 1D). These lamina-associated neurons include five lamina output neurons, six putative feedback neurons, and one lamina intrinsic cell (Fischbach and Dittrich, 1989). Eight of these neuron classes are columnar—there is one cell per retinotopic column (Figure 1C). The columnar neurons include the feedforward lamina monopolar cells, L1–L5 (Figure 1C, red), which send axonal processes into the medulla. The largest of the monopolar cells, L1, L2, and L3, receive direct synaptic input from the R1–R6 photoreceptors, but L4 and L5 do not (Meinertzhagen and O’Neil, 1991 and Rivera-Alba et al., 2011). In addition to these five lamina output neurons, three putative feedback neurons, T1, C2, and C3, are also columnar (Figure 1C, blue).