For some amputees, the pain and disability of losing an arm or leg are followed by a lifetime of other disturbing effects. For them, a touch on the face feels like a touch on the lost limb; the missing fingers or toes seem to be moving toward the remaining stump; and pain can persist in the limb that is long gone.
Many people are at risk for these phantom-limb effects; about 100,000 amputations occur each year in the United States alone. In this week's issue of the journal Science, Edward Jones, director of the UC Davis Center for Neuroscience, and co-author Tim Pons, professor of neurosurgery at Wake Forest University School of Medicine, paint a new picture of the changes that occur deep in the brain after amputation.
Their findings could point to new means of preventing or treating post-amputation problems. And, coming on the heels of other news that adults, even people in their 60s and 70s, grow new brain cells, the report adds to the growing awareness that the adult brain is far more responsive and adaptable than had been believed.
Jones and Pons studied the brains from eight monkeys in which, 12 to 20 years before their deaths, the nerves in one arm had been surgically severed at the spinal column. All the animals were from a group called the Silver Spring monkeys, the subjects of an intense debate in 1985 about animal experimentation.
The research showed that the marooned nerve cells in the brain that no longer received information from the arm shrank by almost half. The resulting space was filled by neighboring nerve cells that normally carried information from the face.
In this new organization, sensory messages from the face were carried to the part of the cerebral cortex that normally receives sensations from the arm. There was also increased activity in adjacent brain cells that normally carry painful messages.
"These findings show that the effects on the brain are progressive over time, which had not been thought before," Jones says. "And if we could harness these effects therapeutically, we would be able to plan strategies for preventing post-amputation pain and for recovery of function after nerve damage."
Funding for the study was provided by the U.S. Public Health Service of the National Institutes of Health. For most of the study period, Edward Jones was on the faculty of the University of California, Irvine; he joined the UC Davis faculty on July 1, 1998.
Jones and Tim Pons will describe their research on Tuesday, Nov. 10, at the annual meeting of the Society for Neuroscience in Los Angeles. Jones is the society's president-elect.
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