Scientists (Dr. Douglas Kerr, a neurologist at Johns Hopkins University who led the work being published on Monday in the journal Annals of Neurology) have used stem cells and a soup of nerve-friendly chemicals not only to bridge a damaged spinal cord but also re-grow the circuitry needed to move a muscle, helping partially paralysed rats walk.

The work marks a tantalising new step in stem cell research that promises to one-day help repair from nerve-destroying illnesses such as Lou Gehrig’s disease, or from spinal cord injuries.

The new work essentially installs new wiring, replacing motor neurons, specialised nerve cells for movement, which have died, to make a new circuit that grows neuronal connections out of the spinal cord and down to a leg muscle.