Interaction of central and peripheral mechanisms during walking in first instar stick insects, Extatosoma tiaratum

ABSTRACT. Individual stick insects were studied walking on a tread-wheel. When a leg caught hold of a small fixed rod beside the wheel it: (a) applied a rhythmically modulated backward directed force (with the modulation frequency identical to the stepping frequency of the other legs); or (b) regularly lifted off the stick during the phase of minimum force, and then returned to the stick; or (c) it stepped onto the wheel. If the wheel was stopped, the applied force increased. It is deduced that this behaviour is driven by central rhythmicity of unknown origin. All the known sensory inputs to this behaviour are superimposed on this central oscillation. A hypothesis is discussed which qualitatively fits all the experimental results on the effect of these sensory influences on the timing of an individual leg's movements in stick insects.