Distributed control of song pattern generation in crickets revealed by lesions to the thoracic ganglia

The distribution of the calling song motor pattern generator in the thoracic ganglia of the cricket was investigated by selective lesions of thoracic ganglia and connectives. The song motor pattern was monitored by recording wing movements, muscle activity, and sound. Hemisection of the prothoracic or the mesothoracic ganglion did not impair song motor pattern generation or bilateral coordination of the wings. Additional lesion of one connective anterior to the respective hemisected ganglion also had no effect on the motor pattern. Two lesions suggest that neuronal structures in the metathoracic ganglion play an important role in rhythm generation, although the sound producing forewings are driven almost exclusively by mesothoracic musculature: 1. Hemisection of the metathoracic ganglion led to a significant increase of syllable period. In some males the left/right coordination was more variable, while in others the motor pattern was expressed only on one side. 2. Hemisection of the mesothoracic ganglion in combination with unilateral lesion of the meso- to metathoracic connective resulted in motor pattern expression and wing movement only on the side of the intact connective. The results indicate that the basis for song rhythm generation of the mesothoracic wing appendages is accomplished by the interaction of hemioscillators in the metathoracic ganglion.