Shell movements associated with locomotion of Lymnaea are driven by a central pattern generator

1.1. Locomotion in Lymnaea is accompanied by rhythmic shell movements, caused by contractions of the columellar muscles.2.2. Column motoneurones are located in the pedal ganglia and have ipsilateral peripheral projections to the columellar muscles.3.3. The motoneurones are driven by a central pattern generator (CPG) which occasionally becomes spontaneously active in isolated brains.4.4. The motoneurones are not synaptically connected to one another, nor do they usually exhibit feedback to the CPG. In 40 preparations only one motoneurone has been found to modify the output of the CPG.