Spinal mechanisms in the control of movement. In the 1910–1920s Paul Hoffmann demonstrated that percutaneous electrical stimulation of the posterior tibial nerve in human subjects produced a synchronised response in the soleus muscle with the same central delay as the Achilles tendon jerk. This landmark study long preceded Lloyd's identification of the corresponding pathway in the cat (1943). Subsequently, much of the primary knowledge about the spinal circuitry has come from animal experiments, but human studies have retained a unique role: the ability to shed direct light on how spinal mechanisms are used in the control of voluntary movement. In the 1940–1950s, many spinal pathways were analysed in ‘reduced’ animal preparations with regard to their synaptic input and to their projections to other neurones.

Modern views about spinal pathways began to emerge when Anders Lundberg and colleagues showed in the 1960s and 1970s that, in the cat, each set of spinal interneurones receives extensive convergence from different primary afferents and descending tracts, and that the integrative function of spinal interneurones allows the motoneurones to receive a final command that has been updated at a premotoneuronal level. Methods have now been developed to enable indirect but nevertheless valid measurements of spinal interneuronal activity in human subjects, and these techniques have demonstrated reliability, particularly when congruent results are obtained with independent methods. Their use has allowed elucidation of how the brain modulates the activity of specific spinal interneurones to control movement.