Abstract
Cockroaches are remarkably stable runners, exhibiting rapid recovery from external perturbations. To uncover the mechanisms behind this important behavioral trait, we recorded leg kinematics of freely running animals in both undisturbed and perturbed trials. Functional coupling underlying inter-leg coordination was monitored before and during localized perturbations, which were applied to single legs via magnetic impulses. The resulting transient effects on all legs and the recovery times to normal pre-perturbation kinematics were studied. We estimated coupling architecture and strength by fitting experimental data to a six-leg-unit phase oscillator model. Using maximum-likelihood techniques, we found that a network with nearest-neighbor inter-leg coupling best fitted the data and that, although coupling strengths vary among preparations, the overall inputs entering each leg are approximately balanced and consistent. Simulations of models with different coupling strengths encountering perturbations suggest that the coupling schemes estimated from our experiments allow animals relatively fast and uniform recoveries from perturbations.
Highlights
Cockroaches are renowned for their ability to maintain dynamic stability when running over uneven terrain
Inter-leg coordination during locomotion may be achieved by connections between central pattern generator (CPG) networks controlling each leg, by inter-leg afferent signals, and by mechanical coupling among legs during stance
We use sinusoidal coupling functions to describe each leg units’ phase sensitivity to inputs from other legs. Such functions are predicted by analyses of bursting neuron CPG models (Ghigliazza and Holmes, 2004) and further justified by measured phase-response curves that quantify how inputs at different phases are transferred to neighboring legs (Fig. 2)
Summary
Cockroaches are renowned for their ability to maintain dynamic stability when running over uneven terrain Their rapid recovery from unexpected perturbations results from both passive mechanical properties of their musculoskeletal structures and interactions among central and local sensorimotor circuits controlling legs, and body dynamics (Jindrich and Full, 2002; Dudek and Full, 2006; Dudek and Full, 2007; Sponberg and Full, 2008; Sponberg et al, 2011a; Sponberg et al, 2011b). Inter-leg couplings are likely to differ among species, and may depend on locomotive context
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