Decades after David Savage lost his right hand in a machine press accident, the 57-year old has received a hand transplant and recovered some feeling, despite spending 35 years with a prosthetic hook.
Now a brain imaging study explains why.
Decades after David Savage lost his right hand in a machine press accident, the 57-year old has received a hand transplant and recovered some feeling, despite spending 35 years with a prosthetic hook.
Now a brain imaging study explains why. When gently poked in the palm by researchers, Savage activated roughly the same brain region as normal test subjects. The area, called the sensory cortex, maintains a physical map of the body with different portions registering sensations in the face, arms and other body parts.
After losing a hand, the brain slowly cedes real estate in this region to the face, says Scott Frey, a cognitive neuroscientist at the University of Oregon in Eugene. But Savage’s transplanted hand quickly commandeered this area back.
“The brain may be much more capable than we thought of at least getting back some organisation in these maps, even after being deprived after a very long time,” Frey says.
His team tested Savage in a functional-MRI brain scanner four months after he became the third American to successfully receive a grafted hand.
When the researchers stroked a coarse sponge across his right palm, Savage’s sensory cortex lit up in the same spot as four other men.
Frey’s team isn’t sure how Savage’s brain managed to re-map the transplanted hand long after it had stopped receiving any signal from his original hand. One possibility is that Savage’s brain never really lost the connection to his right hand, instead his brain merely dialled down the neurons that map it.
Angela Sirigu, a neuroscientist at the Institute of Cognitive Neuroscience in Lyon, France says this reorganisation happens gradually.
Her team recently tested a hand transplant patient at two time points. “Just after the transplantation there was competition between the face representation and the hand,” she says. “Three months later, this competition disappeared.”
Understanding this process could help develop a next generation of prosthetic limbs, Frey says. Scientists are beginning to connect prostheses to nerves that control limb movement, and sending sensory information from the prosthetic to the brain would make replacement limbs even more useful.
Journal reference: Current Biology (DOI: 10.1016/j.cub.2008.08.051)