Development of motor behaviour.

The development of motor behaviour depends on the differentiation of underlying circuitry. Recent work with the zebrafish brings the simple swimming behaviour of lower vertebrates and their embryos into focus as a suitable model to study the development of motor circuitry and its genetic control. Changes in connectivity and excitability contribute to the development of swimming in this simple system. In the chick embryo, limb motor circuitry is spontaneously active before motor axons reach their muscle targets, and it has properties in common with the spontaneously active networks in the retina. The early rhythmic activity responsible for embryonic movement is probably a generalised property of developing spinal networks that precedes, and may be required for, the completion of functional locomotor circuitry.