FRIDAY, June 21, 2002 (HealthDayNews) -- Scientists are getting a glimpse into how the brain creates a phantom limb, potentially helping them develop new ways to treat amputees who feel pain in body parts that aren't there.
In a very unusual case involving a stroke victim's perception of a third arm, researchers at the University of California at San Francisco found activity in a part of the brain that sends signals to the body, not the other way around.
That suggests the brain's mental image of the body may play a key role in the development of phantom limbs, says Dave McGonigle, a radiology researcher and co-author of a study that appears in the current issue of Brain.
"This may provide the missing link" to explain why some treatments that retrain the brain seem to work in phantom limb patients, McGonigle says.
Experts think amputees have long suffered from perceptions that their missing limbs still exist. However, doctors didn't describe the phenomenon until the Civil War in the 1860s when the advent of anesthesia helped soldiers survive amputation, McGonigle says.
Sufferers "realize that something funny is going on," he says. "'I've lost my limb, but I feel like it's still there.'"
About 80 percent of amputees report phantom sensations, and 70 percent report phantom pain, McGonigle says. Some sufferers say "that 'my phantom limb is clenching and the nails are digging into my palm,'" he adds.
Some people who were born without limbs also report phantom pain, but researchers debate whether the reports are valid, McGonigle says.
The ghost limbs remain a subject of fascination for people both in and out of the medical field.
"How can we have such a strong sensory experience of something that isn't there? Why can some people 'move' their phantom limbs while others can't? Scientists still know very little," says study co-author Chris Frith, a neuroscientist at University College London in the United Kingdom.
Only over the past decade have researchers begun to use high-tech scanning devices to watch how the brain handles phantom limbs, he says.
In his study, McGonigle used a scanning technology known as functional magnetic resonance imaging (fMRI) to examine the brain of a female stroke patient. "The technology allows us to eavesdrop on the workings of the brain without exposing it to electrodes or recording devices," he says.
The 42-year-old Finnish woman had been embarrassed to report to her doctors that she felt as though she had a second right arm. When she moved her actual arm, the phantom arm would appear in her mind about 60 to 90 seconds later in the location where the actual arm had been.
When the woman felt her phantom arm, the fMRI picked up activity in a part of her brain that controls movement, McGonigle says. Apparently, when she moved her actual arm, a "shadow" of the action stayed imprinted on the brain and created the ghost limb, he says.
"The study shows that our perception doesn't only arise from sensory stimulation -- vision, hearing, touch -- but also from representations of action [in the mind]," Frith says.
McGonigle acknowledges the case of the stroke patient is very unusual. Unlike amputees, she is not missing any actual limbs. However, the research does suggest an explanation for why some people with phantom limbs can be treated by "retraining" the parts of their brains that control action, he says.
What To Do
Learn about phantom limbs from Macalester University and ScienceNet.
