Straight walking and turning on a slippery surface

Abstract

SUMMARYIn stick insects, walking is the result of the co-action of different pattern generators for the single legs and coordinating inter-leg influences. We have used a slippery surface setup to understand the role the local neuronal processing in the thoracic ganglia plays in the ability of the animal to show turning movements. To achieve this, we removed the influence of mechanical coupling through the ground by using the slippery surface and removed sensory input by the successive amputation of neighboring legs. We analyzed the walking pattern of the front, middle and hind legs of tethered animals mounted above the surface and compared the kinematics of the straight walking legs with those of the curve walking inside and outside legs. The walking pattern was monitored both electrically through tarsal contact measurement and optically by using synchronized high-speed video. The vectors of leg movement are presented for the intact and a reduced preparation. Animals showed the ability to walk in a coordinated fashion on the slippery surface. Upon change from straight to curve walking, the stride length for the inside legs shortens and the vector of movement of the inner legs changes to pull the animal into the curve, while the outer legs act to pull and push it into the turn. In the reduced two-leg and in the single-leg preparation the behavior of the legs remained largely unchanged in the behavioral contexts of straight walking or turning with only small changes in the extreme positions. This suggests that the single stepping legs perform given motor programs on the slippery surface in a fashion that is highly independent not only of mechanical coupling between but also of the presence of the other legs.

Segment-specific and state-dependent targeting accuracy of the stick insect

“…Optical recordings of the steps were performed and analyzed as previously (Gruhn et al, 2009a). In brief, walking sequences were recorded with a high-speed video camera (Marlin F-033C; Allied Visions Technologies, Stadtroda, Germany) that was externally triggered at 100framess with fluorescent pigments (Dr Kremer Farbmühle, Aichstetten, Germany) mixed with dental cement.…”

“…This constitutes a setup where the first step of the hindleg is virtually mechanically uncoupled from the standing middle leg. A different approach to study the neuronal control of stepping used animals tethered above a slippery surface, and showed that stick insects are able to perform normal walking movements under this condition (Graham and Cruse, 1981;Cruse and Epstein, 1982;Epstein and Graham, 1983;Graham and Epstein, 1985;Gruhn et al, 2006;Gruhn et al, 2009a). However, information about targeting movements of the legs on the slippery surface is relatively scarce and inconclusive.…”

Quadrupedal gaits in hexapod animals - inter-leg coordination in free-walking adult stick insects

“…Of course, insect inter-leg coordination patterns depend on the behavioural context and environmental conditions such as surface structure, slopes, orientation of the body or specifics of an experimental setup (e.g. Spirito and Mushrush, 1979;Delcomyn, 1981;Graham, 1985;Duch and Pflüger, 1995;Dürr, 2005;Gruhn et al, 2009;Bender et al, 2011). And thus, in contrast to walks on the sphere, Graham reported that free-walking adult stick insects (Carausius morosus) on a horizontal surface almost exclusively use a 'biquadruped'; that is, a tetrapod gait (Graham, 1972).…”

Neural activity in the central complex of the cockroach brain is linked to turning behaviors

“…Direct control of leg movements resides in the local control circuits of the thoracic ganglia in arthropods or spinal cords of vertebrates (Deliagina et al, 1999). In insects, these circuits include central pattern generators and local reflexes that produce basic leg cycles, and then change to produce turns or adjust posture Mentel et al, 2008;Gruhn et al, 2009;Hellekes et al, 2012;Mu and Ritzmann, 2005;Ritzmann and Büschges, 2007). In order to respond to barriers properly, objects must be detected and evaluated by sensory structures that largely reside on the animal's head (Harley et al, 2009;Okada and Toh, 2000;Schütz and Dürr, 2011).…”