In research made public in the first quarter of 2009, a French surgical team consisting of Angela Sirigu and colleagues at the Institute for Cognitive Science in Lyon, France, made a stunning discovery with regards to transplanted hands: Under proper stimulation conditions, the nerves grow back, and the hands begin to function normally. The implications for both natural and prosthetic body parts are huge.

We have known for quite some time that the motor cortex maintains a map of the physical state of the body, with different areas registering sensations in different body parts. When a part is removed, the control circuitry is still intact. This lapses into disuse for the most part, occasionally processing random signals from the severed limbs. This is known as phantom limb pain. Whilst the brain for the most part is plastic, this circuitry is never fully reclaimed.

The researchers hit upon the idea of directing magnetic impulses to over-stimulate the area of the brain in two patients who had both had double hand transplants. The over-stimulation kicked long-dormant circuitry into overdrive, and something amazing occurred. The nerves in the arm lit up with signals, and somehow, the signals jumped the gap between original nerves and the transplanted hand nerves. A broken connection was made, which was enough to stimulate the peripheral nervous system.

The severed nerves in both cases, began to grow back. Because the nerves had been carefully arranged in the transplants, to match as closely as possible to the locations of the original nerves, the original nerves, able to make an intermittent connection, actually began to regenerate.

Averaging 1mm of new growth per day, over the next 26 months, the nerves regrew and stitched themselves back together, in both patients. The mesh is not perfect, but control of their hands - moving the fingers, muscle twitching and some flexibility - has been restored to both patients.

We are a long way from fully understanding the mechanisms that led to the nerve regrowth, but, it does open up another interesting possibility. If the wiring of the body can regenerate when it senses compatible wiring where the brain remembers there being wiring before, it may actually be possible once we analyse the process, to connect nerves directly to prosthetic wiring.

Definitely a distant future aspect, this still offers tantalising evidence that the nervous system is capable of repairing and bonding with nerves from a foreign system.

References

Double Hand Transplant Reawakens Brain Control