HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 94/3/2150    most recent 00411.2005v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (11) Citing Articles via Google Scholar Google Scholar Articles by Gabbiani, F. Articles by Laurent, G. Search for Related Content PubMed PubMed Citation Articles by Gabbiani, F. Articles by Laurent, G.

Time-Dependent Activation of Feed-Forward Inhibition in a Looming-Sensitive Neuron

¹Department of Neuroscience, Baylor College of Medicine, Houston, Texas; ²Computational and Applied Mathematics, Rice University, Houston, Texas; and ³Division of Biology, California Institute of Technology, Pasadena, California

Submitted 21 April 2005; accepted in final form 28 May 2005

The lobula giant movement detector (LGMD) is an identified neuron in the locust visual system that responds preferentially to objects approaching on a collision course with the animal. For such looming stimuli, the LGMD firing rate gradually increases, peaks, and decays toward the end of approach. The LGMD receives both excitatory and feed-forward inhibitory inputs on distinct branches of its dendritic tree, but little is known about the contribution of feed-forward inhibition to its response properties. We used picrotoxin, a chloride channel blocker, to selectively block feed-forward inhibition to the LGMD. We then computed differences in firing rate and membrane potential between control and picrotoxin conditions to study the activation of feed-forward inhibition. For looming stimuli, a significant activation of inhibition was observed early, as objects exceeded on average 23° in angular extent at the retina. Inhibition then increased in parallel with excitation over the remainder of approach trials. Experiments in which the final angular size of the approaching objects was systematically varied revealed that the relative activation of excitation and inhibition remains well balanced over most of the course of looming trials. Feed-forward inhibition actively contributed to the termination of the response to approaching objects and was particularly effective for large or slowly moving objects. Suddenly appearing and receding objects activated excitation and feed-forward inhibition nearly simultaneously, in contrast to looming stimuli. Under these conditions, the activation of excitation and feed-forward inhibition was weaker than for approaching objects, suggesting that both are preferentially tuned to approaching objects. These results support a phenomenological model of multiplication within the LGMD and provide new constraints for biophysical models of its responses to looming and receding stimuli.

This article has been cited by other articles:

				F. C. Rind, R. D. Santer, and G. A. Wright Arousal Facilitates Collision Avoidance Mediated by a Looming Sensitive Visual Neuron in a Flying Locust J Neurophysiol, August 1, 2008; 100(2): 670 - 680. [Abstract] [Full Text] [PDF]

				R. Khanbabaie, A. S. Mahani, and R. Wessel Contextual Interaction of GABAergic Circuitry With Dynamic Synapses J Neurophysiol, April 1, 2007; 97(4): 2802 - 2811. [Abstract] [Full Text] [PDF]

				S. P. Peron, H. G. Krapp, and F. Gabbiani Influence of Electrotonic Structure and Synaptic Mapping on the Receptive Field Properties of a Collision-Detecting Neuron J Neurophysiol, January 1, 2007; 97(1): 159 - 177. [Abstract] [Full Text] [PDF]

				F. Gabbiani and H. G. Krapp Spike-Frequency Adaptation and Intrinsic Properties of an Identified, Looming-Sensitive Neuron J Neurophysiol, December 1, 2006; 96(6): 2951 - 2962. [Abstract] [Full Text] [PDF]

				R. D. Santer, F. C. Rind, R. Stafford, and P. J. Simmons Role of an Identified Looming-Sensitive Neuron in Triggering a Flying Locust's Escape J Neurophysiol, June 1, 2006; 95(6): 3391 - 3400. [Abstract] [Full Text] [PDF]

				T. Preuss, P. E. Osei-Bonsu, S. A. Weiss, C. Wang, and D. S. Faber Neural representation of object approach in a decision-making motor circuit. J. Neurosci., March 29, 2006; 26(13): 3454 - 3464. [Abstract] [Full Text] [PDF]

				B. B. Guest and J. R. Gray Responses of a Looming-Sensitive Neuron to Compound and Paired Object Approaches J Neurophysiol, March 1, 2006; 95(3): 1428 - 1441. [Abstract] [Full Text] [PDF]