A model based on inhibitory interactions between oscillators representing leg activity has been constructed to explain the step pattern changes in both modes of walking and the temporal asymmetry of the adult pattern and appears to be applicable to the walking behaviour of other insects including the cockroach.
Adult stick insects walk on a mercury surface at step frequencies in the range 1-4 Hz with a coordination similar to that found in free-walking adults at their maximum step frequency of 3 Hz, indicating that feedback from the periphery determines the step period.
Fast motor output appeared to be superimposed on the forward walking motor pattern to produce the movements required for backward walking in this insect.
The stepping patterns of intact, amputated and leg restrained first instar stick insects were examined by analysing video tape records of their free walking behaviour to test certain assumptions of a model for generating the step pattern and to investigate how the tonic influence of proprioceptive input might be incorporated into the model.
The walking coordination and motor output of intact adult stick insects was examined when they were supported above an oiled glass surface and found that under these conditions an individual leg moved much more slowly than its neighbours, producing 2:1 coordination patterns.
The isolation of the ventral nerve cord by circum-oesophageal nerve lesion produces a preparation which is capable of walking and righting itself when placed on its back, which is examined as a function of time, temperature and external stimulation.
Simulation of the behaviour of a model proposed to explain certain asymmetries in the free walking step patterns of adult stick insects suggests that there are subtle differences in the walking system at these two stages of growth.
Co-ordinated walking in this insect appears to be a discrete process in which the performance of a protraction stroke activates a co-ordinating influence and, in conjunction with a frequency hierarchy, maintains the required time relationship between the legs.
The retractor coxae muscles of the mesothorax were examined by reflex stimulation and simultaneously recording intracellular muscle fiber potentials and the activity in nerve nl5 to show the morphology of both groups of neurons.