title: Two identified looming detectors in the locust: ubiquitous lateral connections among their inputs contribute to selective responses to looming objects.
abstract: In locusts, two lobula giant movement detector neurons (LGMDs) act as looming object detectors. Their reproducible responses to looming and their ethological significance makes them models for single neuron computation. But there is no comprehensive picture of the neurons that connect directly to each LGMD. We used high-through-put serial block-face scanning-electron-microscopy to reconstruct the network of input-synapses onto the LGMDs over spatial scales ranging from single synapses and small circuits, up to dendritic branches and total excitatory input. Reconstructions reveal that many trans-medullary-afferents (TmAs) connect the eye with each LGMD, one TmA per facet per LGMD. But when a TmA synapses with an LGMD it also connects laterally with another TmA. These inter-TmA synapses are always reciprocal. Total excitatory input to the LGMD 1 and 2 comes from 131,000 and 186,000 synapses reaching densities of 3.1 and 2.6 synapses per μm2respectively. We explored the computational consequences of reciprocal synapses between each TmA and 6 others from neighbouring columns. Since any lateral interactions between LGMD inputs have always been inhibitory we may assume these reciprocal lateral connections are most likely inhibitory. Such reciprocal inhibitory synapses increased the LGMD's selectivity for looming over passing objects, particularly at the beginning of object approach.
authors: Institute of Neuroscience/Centre for Behaviour and Evolution, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK.|Institute of Cell Biology, Histology and Embryology/Research Unit Electron Microscopic Techniques, 8010 Graz, Austria.
authors: F Claire
authors: FC
authors: Rind
authors: Institute of Neuroscience/Centre for Behaviour and Evolution, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK.|Institute of Cell Biology, Histology and Embryology/Research Unit Electron Microscopic Techniques, 8010 Graz, Austria.
authors: Stefan
authors: S
authors: Wernitznig
authors: Institute for Electron Microscopy and Nanoanalysis/NAWI Graz, Graz University of Technology, 8010 Graz, Austria.|Centre for Electron Microscopy, 8010 Graz, Austria.
authors: Peter
authors: P
authors: Pölt
authors: Institute for Electron Microscopy and Nanoanalysis/NAWI Graz, Graz University of Technology, 8010 Graz, Austria.|Centre for Electron Microscopy, 8010 Graz, Austria.
authors: Armin
authors: A
authors: Zankel
authors: Institute of Cell Biology, Histology and Embryology/Research Unit Electron Microscopic Techniques, 8010 Graz, Austria.
authors: Daniel
authors: D
authors: Gütl
authors: Departamento de Fisiologıa, Biologıa Molecular y Celular/FCEN, Universidad de Buenos Aires/IFIBYNE-CONICET, Buenos Aires 1428, Argentina.
authors: Julieta
authors: J
authors: Sztarker
authors: Institute of Neuroscience/Centre for Behaviour and Evolution, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK.|BioTechMed-Graz, 8010 Graz, Austria.
authors: Gerd
authors: G
authors: Leitinger