An oscillatory neuronal circuit generating a locomotory rhythm.

A quartet of interconnected interneurons whose periodic activity appears to generate the traveling body wave of the swimming leech has been identified on each side of segmental ganglia of the ventral nerve cord of Hirudo medicinalis. Theoretical analysis and electronic analog models of the identified intra- and interganglionic synaptic connections of the segmentally iterated interneurons showed that they form an oscillatory network with cycle period and intra-and intersegmental phase relations appropriate for the swimming movement.