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Research - Locomotion
   
Effective behavior is the result of the properly timed and coordinated action of muscles. Therefore, a fundamental question in motor systems neurobiology is how the central nervous system of any animal is able to generate such properly timed and coordinated action. This question is often investigated by studying a repetitive behavior like walking because such repetitive (rhythmic) behavior is usually easier to evoke and in principle easier to understand than non-rhythmic activity.

Insect walking has often been used as a model system for the study of rhythmic behavior, and research over the past several decades has revealed much about the insect locomotor system. First, in common with other rhythmic behavior, the alternating action of antagonistic muscle pairs (leg extensors and flexors) is generated by networks of neurons that can produce rhythmic output without needing any external timing signals. Such networks are called central pattern generators (CPGs). There is at least one CPG per leg; some evidence suggests that there may even be one per joint. The CPGs are coupled together via interneurons so that the activity of one can influence the activity of another. Second, sensory feedback from the moving legs is in most cases critical for the proper coordination of the legs during walking. In some insects (such as stick insects like Carausius morosus) the requirement for sensory feedback is so strong that coordination virtually disappears if it is eliminated. In other insects (such as cockroaches like Periplaneta americana), the need for sensory feedback may be reduced during fast walking.

My research has focussed on two main issues. First, how are CPGs for different legs coupled together? This question can be answered in part by experiments in which leg movements are disrupted in some way. Results suggest that whereas ipsilateral (same side) CPGs can change coordination (i.e., coupling is loose), contralateral pairs of CPGs are tightly coupled and hence always show the same coordination relative to one another. Second, what sensory feedback from the legs is most critical for coordination, and how does this feedback affect coordination? Research in several labs has suggested that in insects cuticular mechanoreceptors (campaniform sensilla) that respond to strain in the cuticle, are critical.

In my current research I use computer simulation to address both questions. Simulating CPGs and testing the effectiveness of various means of coupling between them in a virtual (simulated) insect is a way to answer the first question. Simulating campaniform sensilla action during walking is a way to answer the second. More information about my simulation research may be found on the simulation research page.

Relevant Publications
Delcomyn, F. 1985. Factors regulating insect walking. Annual Rev. Entomol. 30, 239-256.   (Review)
Delcomyn, F. 1985. Insect locomotion: past, present and future. In, Insect Locomotion, Ed. by M. Gewecke and G. Wendler, pp. 1-18. Hamburg: Paul Parey.   (Review)
Delcomyn, F. 1985. Walking and running. In, Comprehensive Insect Physiology, Biochemistry and Pharmacology, Ed. by G.A. Kerkut and L.I. Gilbert, Vol. 5, Chapter 11, pp. 439-466. London: Pergamon Press.   (Review)
Delcomyn, F. 1987. Motor activity during searching and walking movements of cockroach legs. J. Exp. Biol. 133, 111-120.
Delcomyn, F. 1988. Motor activity in the stump of an amputated leg during free walking in cockroaches. J. Exp. Biol. 140, 465-476.
Delcomyn, F. and J.H. Cocatre-Zilgien. 1988. Individual differences and variability in the timing of motor activity during walking in insects. Biol. Cybern. 59, 379-384.
Delcomyn, F. 1989. Walking in the American cockroach: the timing of motor activity in the legs during straight walking. Biol. Cybern. 60, 373-384.
Delcomyn, F. 1991. Activity and directional sensitivity of leg campaniform sensilla in a stick insect. J. Comp. Physiol. A 168, 113-119.
Delcomyn, F. 1991. Perturbation of the motor system in freely walking cockroaches. I. Rear leg amputation and the timing of motor activity in leg muscles. J. Exp. Biol. 156, 483-502.
Delcomyn, F. 1991. Perturbation of the motor system in freely walking cockroaches. II. The timing of motor activity in leg muscles after amputation of a middle leg. J. Exp. Biol. 156, 503-517.
Delcomyn, F. 1992. Insect walking. NEUROSCIENCE YEAR: Supplement 2 to the Encyclopedia of Neuroscience, Ed. by B. Smith and G. Adelman, pp. 85-87. Boston: Birkh├╝ser.
Delcomyn, F. 1999. Walking robots and the central and peripheral control of locomotion in insects. Auton. Rob. 7, 259-270.
Delcomyn, F. 2004. Insect Walking and Robotics. Annual Rev. Entomol. 49, 51-70
Copyright © 1999-2013 F. Delcomyn
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