Gabbiani, Fabrizio and Krapp, Holger G. and Laurent, Gilles (1999) Computation of Object Approach by a Wide-Field, Motion-Sensitive Neuron. Journal of Neuroscience, 19 (3). pp. 1122-1141. ISSN 0270-6474. http://resolver.caltech.edu/CaltechAUTHORS:20130816-103142544
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The lobula giant motion detector (LGMD) in the locust visual system is a wide-field, motion-sensitive neuron that responds vigorously to objects approaching the animal on a collision course. We investigated the computation performed by LGMD when it responds to approaching objects by recording the activity of its postsynaptic target, the descending contralateral motion detector (DCMD). In each animal, peak DCMD activity occurred a fixed delay δ (15 ≤ δ ≤ 35 msec) after the approaching object had reached a specific angular threshold θthres on the retina (15° ≤ θthres ≤ 40°). θthres was independent of the size or velocity of the approaching object. This angular threshold computation was quite accurate: the error of LGMD and DCMD in estimating θthres(3.1–11.9°) corresponds to the angular separation between two and six ommatidia at each edge of the expanding object on the locust retina. It was also resistant to large amplitude changes in background luminosity, contrast, and body temperature. Using several experimentally derived assumptions, the firing rate of LGMD and DCMD could be shown to depend on the product ψ(t − δ) · e^(−αθ(t−δ0)), where θ(t) is the angular size subtended by the object during approach, ψ(t) is the angular edge velocity of the object and the constant, and α is related to the angular threshold size [α = 1/tan(θthres^(/2))]. Because LGMD appears to receive distinct input projections, respectively motion- and size-sensitive, this result suggests that a multiplication operation is implemented by LGMD. Thus, LGMD might be an ideal model to investigate the biophysical implementation of a multiplication operation by single neurons.
|Additional Information:||© 1999 Society for Neuroscience. Received July 8, 1998; revised Nov. 4, 1998; accepted Nov. 19, 1998. This work was supported by grants from the National Science Foundation (NSF), the NSF Presidential Faculty Fellow Program, the Sloan Center for Theoretical Neuroscience, the Center for Neuromorphic Systems Engineering as part of the NSF Engineering Research Center program, and a travel grant from the Deutsche Forschungsgemeinschaft. We thank J. Burns, J. Douglass, S. Panish, and M. Wicklein for help in setting up the stimulation system and Martin Egelhaaf for careful reading and valuable comments on this manuscript.|
|Group:||Koch Laboratory, KLAB|
|Subject Keywords:||looming; multiplication; locust; LGMD; DCMD; lobula; collision-avoidance|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||KLAB Import|
|Deposited On:||26 Jan 2008 03:52|
|Last Modified:||20 Nov 2015 18:39|
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