The most important motor function of the spinal cord is to transmit the command for movement from higher centres to spinal motoneurones. In primates, there are monosynaptic cortico-motoneuronal projections, whereas, in the cat, the corticospinal command to forelimb motoneurones is transmitted exclusively through oligosynaptic pathways with intercalated spinal interneurones. Some are located at each segmental level (segmental interneurones). Others are rostral to motoneurones and are referred to as propriospinal neurones in the following (although the term ‘propriospinal’ has a more general meaning: that of an intrinsic spinal cord neurone, the axon of which terminates in remote spinal cord segments).

The presence of a significant contribution of the cervical propriospinal system to the control of upper limb movement in higher primates has been debated, but there is mounting evidence that, in macaque monkeys (Sasaki et al., 2004) and in humans (Pierrot-Deseilligny, 2002), a substantial part of the cortical command for movement is transmitted to motoneurones through a ‘propriospinal’ relay located rostral to motoneurones. The existence of a functional propriospinal system in human subjects is of particular interest. Indeed, because of the extensive convergence onto cervical propriospinal neurones of descending and peripheral inputs, the major role of the propriospinal system is probably to enable integration of the descending command en route to the motoneurones with the afferent feedback from the moving limb.