Learning from the spinal cord

The graceful control of multi-articulated limbs equipped with slow, non-lin ear actuators (muscles) is a difficult problem for which robotic engineerin g affords no general solution. The vertebrate spinal cord provides an exist ence proof that such control is, indeed, possible. The biological solution is complex and incompletely known, despite a century of meticulous neurophy siological research, celebrated in part by this symposium. This is frustrat ing for those who would reanimate paralysed limbs either through promoting regeneration of the injured spinal cord or by functional electrical stimula tion. The importance of and general role played by the spinal cord might be more easily recognized by analogy to marionette puppets, another system in which a brain (the puppeteer's) must cope with a large number of partially redundant actuators (strings) moving a mechanical linkage with complex int rinsic properties.