When a phantom limb forms, there is no default position that it moves into, according to new research from Australia.
The phenomenon of phantom limbs is seen in some people following an amputation who experience sensations indicating that the limb still exists, or spinal cord injuries with illusory limb sensations, both sometimes accompanied by pain.
This seeming paradox can be recreated using anesthesia. Often sufferers perceive their phantom limbs to be in contorted positions.
Understanding the neural mechanisms underlying such body image distortions will enable the development of better treatments.
“Our research suggests that the state of nerves in the limb at the time the phantom is forming is very important in determining how the phantom develops,” said study co-author Simon Gandevia at Neuroscience Research Australia (NeuRA) in a press release.
Gandevia and colleagues temporarily anesthetized participants’ hands to induce a phantom limb. They found that the amount of stimulation received by the nerves during loss of sensation determined the phantom hand’s final perceived position.
“Surprisingly, if the wrist and fingers were held straight before and during anesthesia, the final phantom hand was bent at the wrist and fingers, but if the wrist and fingers were flexed before and during anesthesia, the final phantom was extended at wrist and fingers,” wrote the researchers in the study abstract.
“This might also be true for phantom pain,” Gandevia said. “In other words, the amount and type of nerve stimulation around the time of amputation or injury could also be important in determining the type and degree of pain perceived in the phantom limb.”
The scientists also studied the perception of hand size during the nerve block, and found that it increased as anesthesia progressed.
The findings were published in The Journal of Physiology on Dec. 1.
