Development of motor behaviour

The development of motor behaviour depends on the differentiation of underl ying circuitry. Recent work with the zebrafish brings the simple swimming b ehaviour of lower vertebrates and their embryos into focus as a suitable mo del to study the development of motor circuitry and its genetic control. Ch anges in connectivity and excitability contribute to the development of swi mming in this simple system. In the chick embryo, limb motor circuitry is s pontaneously active before motor axons reach their muscle targets, and it h as properties in common with the spontaneously active networks in the retin a. The early rhythmic activity responsible for embryonic movement is probab ly a generalised property of developing spinal networks that precedes, and may be required for, the completion of functional locomotor circuitry.