Brain sensory region reactivated decades after hand amputation: transplant restores partial use of original neural pathway.
Four months after his December 2006 transplant, Savage's partial sense of touch in the new hand activated the same brain area that would have controlled his original right hand 35 years earlier, say neuroscientist Scott Frey of the University of Oregon in Eugene and colleagues.
When Savage had both hands, part of his right brain responded to his left hand, and a corresponding part of his left brain responded to his right hand. But after the amputation of his right hand following a machine-press accident at age 19, that same part of his left brain would have been sensory-deprived. It would have adopted duties of adjacent sensory areas, such as those for the right arm and possibly face.
Much research has documented that such neural reorganization begins within hours of limb loss or debilitation.
Yet decades later, with a new hand in place, the former "hand area" of Savage's brain has reclaimed its old territory, Frey's team reports in the Oct. 14 Current Biology.
"The capacity of the brain to reverse reorganizational changes is all the more striking in light of the fact that his brain was fully mature when the amputation occurred," Frey says.
Although the researchers have no data about Savage's brain from just before or just after the amputation, sensory areas responsible for his missing right hand must have assumed new duties, says neuroscientist Jon Kaas of Vanderbilt University in Nashville. At a minimum, the neural map for Savage's right hand would have begun to respond to stimulation of parts of his right arm, Kaas suggests.
"It's remarkable that an original neural pathway for the hand can be reinstated after years and years," Kaas says,
In April 2007, functional MRI recorded Savage's brain activity while each of his hands, along with each of his cheeks, was stroked with a coarse sponge. The same experiment was carried out on four men who had never experienced an amputation. Savage reported full left-hand and till facial sensation, as well as sensation in his right palm near the thumb. During right-hand testing, Savage displayed much the same left-brain activation that the other men did.
Savage's recovery so far is limited to major nerves in the right hand, not to peripheral nerve connections for individual fingers, Frey says. It's unclear how the neural map of the right hand will adapt as Savage's finger nerves regenerate and finger sensation develops.
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|Title Annotation:||Body & Brain|
|Date:||Nov 8, 2008|
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