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 th oracic ganglia of the cricket was investigated by selective lesions of thoracic ganglia and connectives. The song motor pattern was monitore d by recording wing movements, muscle activity, and sound. Hemisection of the prothoracic or the mesothoracic ganglion did not impair song m otor pattern generation or bilateral coordination of the wings. Additi onal lesion of one connective anterior to the respective hemisected ga nglion also had no effect on the motor pattern. Two lesions suggest th at 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. H emisection of the mesothoracic ganglion in combination with unilateral lesion of the meso- to metathoracic connective resulted in motor patt ern expression and wing movement only on the side of the intact connec tive. The results indicate that the basis for song rhythm generation o f the mesothoracic wing appendages is accomplished by the interaction of hemioscillators in the metathoracic ganglion.