Signs of Sensory Recovery in New Hand

Photo: The brain with colored spots showing activation

The left cerebral hemisphere acti-
vated during sensory stimulation
of the transplanted right palm;
© Scott Frey

The finding centres only on the man's right palm of a donated hand, which was attached along with major nerves, bones, tendons, and muscle. Still to be determined, lead author Scott H. Frey said, is how the brain’s map of the individual fingers will evolve with increasing sensation. Just four months post-surgery, initial touch sensations were reported on the thenar eminence - muscle on the palm just below the thumb - and on the lateral base of the thumb near the radial nerve.

Functional magnetic resonance imaging was used to record brain activity while sensory stimuli were delivered to the hands and faces of the transplant recipient and four control participants. Results showed that sensory signals from the transplanted hand are being processed in the same brain regions that would have formerly handled sensations from the hand prior to amputation.

"This individual is very unique from a brain standpoint," Frey said. "We know that when someone loses a hand, there are reorganisational changes that take place in areas of the brain that have received sensory input from that hand. Yet, even after 35 years, the restoration of sensory input seems capable of recapturing the former territory of the hand. The capacity of the brain to reverse these changes is all the more striking in light of the fact that his brain was fully mature when the amputation occurred.”

Reorganisation in sensory regions begins within hours of a limb loss. Research has shown that neurons that had been devoted to receiving sensory inputs from the limb take on new duties. Exactly what happens is not entirely clear, nor is it certain how long such changes continue, Frey said, "but one way to think about it is that none of the brain's real estate is left vacant for very long". Over time, the injured man reported gradual reductions of phantom sensations and pain often reported by amputees.

"What this hand transplant allows us to ask for the very first time in history is: Following reorganisational changes, is it possible to reverse the restoration of sensory input into the brain? The answer, which appears to be yes, extends well beyond the case of hand transplants," Frey said.

MEDICA.de; Source: University of Oregon