Endogenous patterns of activity are required for the maturation of a motor network.

Many parts of the nervous system become active before development is complete, including the embryonic spinal cord. Remarkably, although the subject has been debated for over a century (Harrison, 1904), it is still unclear whether such activity is required for normal development of motor circuitry. In Drosophila, embryonic motor output is initially poorly organized, and coordinated crawling-like behavior gradually emerges over the subsequent phase of development. We show that reversibly blocking synaptic transmission during this phase severely delays the first appearance of coordinated movements. When we interfere with the pattern of neuronal firing during this period, coordination is also delayed or blocked. We conclude that there is a period during which endogenous patterns of neuronal activity are required for the normal development of motor circuits in Drosophila.