Neuronal control of walking: studies on insects

Abstract

The control of walking in insects is to a substantial amount a function of neuronal networks in the thoracic ganglia. While descending signals from head ganglia provide general commands such as for walking direction and velocity, it is the thoracic central nervous system that controls movements of individual joints and legs. The coordination pattern of legs is velocity dependent. However, a clear stereotypic coordination pattern appears only at high velocities. In accordance with the unit burst oscillator concept, oscillatory networks (central pattern generators (CPGs)) interlocked with movement and load sensors control the timing and amplitude of joint movements. For a leg’s movements different joint CPGs of a leg are mainly coupled by proprioceptors. Differential processing of proprioceptive signals allows a task specific modulation of leg movements, for example, for changing movement direction. A switch between walking and searching movements of a leg is under local control. When stepping into a gap missing sensory input and the activation of a local command neuron evokes stereotypic searching movements of the leg.