[ddropcap]P[/dropcap]hantom limb pain is a common problem in people who have had body parts amputated, but the phenomenon is poorly understood. New research suggests that the pain is associated with the continued strength of the image of the missing limb in the brain.
The findings, published on March 5 in the journal Nature Communications, call into question a previous explanation for phantom limb pain, which hypothesized that the distress was caused by the brain picking up signals from other body parts in the absence of sensory input from the missing limb. Researchers from Oxford University discovered that, on the contrary, the patients who experienced the most phantom pain also maintained the strongest map of their missing limb in the brain. The researchers hope that their results can advance rehabilitation strategies and treatment for phantom limb pain.
About 80 percent of people with amputated body parts experience pain where their limb used to be. There are limited treatment options, most of which are based on the alternative theory that phantom limb pain is caused by the maladaptive reorganization of the brain after the loss of a body part. The maladaptive organization theory is supported by years of earlier research, and its proponents could disagree with the Oxford team’s interpretation of their results.
Lynn Ledger, who participated in the study, generally tries to distract herself from her phantom limb pain using her imagination and breathing exercises. She described her pain in a press release accompanying the paper: “Imagine you are wearing a lady’s evening glove that stretches from the fingers up the arm past the elbow. But everywhere the glove covers, it’s as if it’s constantly crushing your arm.”
The researchers used a Magnetic Resonance Imaging machine to compare the brain activity of 18 people who had an amputated hand with 11 people born with only one hand and a control group of people with both hands. All of the amputees retained some sensation in their missing hand, which the researchers instructed them to move while the MRI machine recorded the brain’s response.
While the researchers found that the structure and organization of the missing hand was preserved in the brain, they also noted that the grey matter in the area of the brain representing the hand had shrunk in the amputees. The MRI results suggested that, though the hand representation remained largely intact, there were fewer connections between it and other areas of the brain involved in movement – another factor that correlated with higher pain. The same results were not found in the control group or in the people born with missing limbs.
At this point, it is impossible to tell whether the phantom limb pain is caused by the changes in the brain after amputation or vice versa, but the researchers plan to conduct more tests to determine the exact relationship. Depending on what they find, the current results could herald the development of rehabilitation strategies that aim to re-connect the brain representation of the phantom limb with sensory input.