A modified walking rhythm employed during righting behavior in the cockroach Gromphadorhina portentosa

Electromyograms were recorded from leg muscles of the cockroach Gromphadorhina during walking and righting under free-ranging and tethered conditions. Two muscles which are essentially synergistic during walking become antagonistic during righting (Fig. 3, 4). This explains in part the difference in the direction of the leg stroke in the two behaviors (Fig. 2). Other properties of the muscle activity are very similar during the two rhythms: the same motoneurons appear to be active (Fig. 5, 6); cycle frequencies are the same; the burst length of one motoneuron studied varies with burst frequency in a generally similar manner in both behaviors (Fig. 7); inter-leg coordination is the same (Fig. 9); and transganglionic coupling characteristic of walking can occur while a leg on one side is engaged in walking, and its contralateral homologue is engaged in righting (Fig. 10). Although other properties of the leg rhythms are different in walking and righting, these differences appear to result from dissimilarities in sensory feedback. It is concluded that although the two leg rhythms are superficially quite different, the underlying central neuronal rhythms are very similar, and possibly result from activity in the same central oscillatory cell or circuit.