Summary

The responses of single brain neurones to artificial calling song, to moving striped patterns and to air puffs were recorded while tethered crickets were walking on a sphere in such a way that their intended orientation to the stimuli could be measured. Local and descending brain neurones responsive to only one of the stimuli tested often encoded the directional information contained in the stimulus (e.g. the direction of the sound source or the direction of stripe movement). Brain neurones with little directional sensitivity responded with marked habituation to all stimuli, so that their responses primarily signalled changes in the overall stimulus situation. The responses of some neurones were stronger during walking than when the cricket was standing still. In the case of one descending neurone, which increased its level of activity shortly before and during the walking phases, the mean spike rate was correlated with the forward velocity. By altering the discharge rate of another descending neurone, it was possible to elicit walking in the manner typical of crickets. Maintenance and control of walking by such 'command neurones ' is discussed