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First published online February 12, 2007
Journal of Experimental Biology 210, 865-880 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02707

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Escape behavior and neuronal responses to looming stimuli in the crab Chasmagnathus granulatus (Decapoda: Grapsidae)

Damián Oliva, Violeta Medan and Daniel Tomsic^*

Laboratorio de Neurobiología de la Memoria, Depto. Fisiología, Biología Molecular y Celular, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, IFIBYNE-CONICET, Buenos Aires 1428, Argentina

^* Author for correspondence (e-mail: tomsic{at}fbmc.fcen.uba.ar)

Accepted 4 January 2007

Behavioral responses to looming stimuli have been studied in many vertebrate and invertebrate species, but neurons sensitive to looming have been investigated in very few animals. In this paper we introduce a new experimental model using the crab Chasmagnathus granulatus, which allows investigation of the processes of looming detection and escape decision at both the behavioral and neuronal levels. By analyzing the escape response of the crab in a walking simulator device we show that: (i) a robust and reliable escape response can be elicited by computer-generated looming stimuli in all tested animals; (ii) parameters such as distance, speed, timing and directionality of the escape run, are easy to record and quantify precisely in the walking device; (iii) although the magnitude of escape varies between animals and stimulus presentations, the timing of the response is remarkably consistent and does not habituate at 3 min stimulus intervals. We then study the response of neurons from the brain of the crab by means of intracellular recordings in the intact animal and show that: (iv) two subclasses of previously identified movement detector neurons from the lobula (third optic neuropil) exhibit robust and reliable responses to the same looming stimuli that trigger the behavioral response; (v) the neurons respond to the object approach by increasing their rate of firing in a way that closely matches the dynamics of the image expansion. Finally, we compare the neuronal with the behavioral response showing that: (vi) differences in the neuronal responses to looming, receding or laterally moving stimuli closely reflect the behavioral differences to such stimuli; (vii) during looming, the crab starts to run soon after the looming-sensitive neurons begin to increase their firing rate. The increase in the running speed during stimulus approach faithfully follows the increment in the firing rate, until the moment of maximum stimulus expansion. Thereafter, the neurons abruptly stop firing and the animal immediately decelerates its run. The results are discussed in connection with studies of responses to looming stimuli in the locust.

Key words: visual behavior, escape response, looming detection, looming sensitive neurons, intracellular recording, Crustacea, Chasmagnathus granulatus

This article has been cited by other articles:

				V. Medan, D. Oliva, and D. Tomsic Characterization of Lobula Giant Neurons Responsive to Visual Stimuli That Elicit Escape Behaviors in the Crab Chasmagnathus J Neurophysiol, October 1, 2007; 98(4): 2414 - 2428. [Abstract] [Full Text] [PDF]

				H. Fotowat and F. Gabbiani Relationship between the Phases of Sensory and Motor Activity during a Looming-Evoked Multistage Escape Behavior J. Neurosci., September 12, 2007; 27(37): 10047 - 10059. [Abstract] [Full Text] [PDF]