Why Do Amputees Sense a “Phantom Limb”?

 

Phantom limb syndrome is the sensation that an amputated limb is still attached to the body and functioning normally.

     

   Amputees report feelings of warmth, coldness, tingling, itchiness, numbness,cramping or tickling in the missing limb. An estimated 80 percent of amputees report phantom pain in their amputated limb, including shooting, piercing, burning, or stabbing pain.

   

   What is the exact cause of phantom limb syndrome? For many years, the Favoured theory has been that this condition is the result of “maladaptive brain plasticity.” In short, when the brain ceases to receive signals from a missing body part, input from another body part, such as the face according to some research, begins to dominate that region of the brain. This “remapping” of the brain has long been thought to cause the syndrome. Results of a 2013 study conducted by Oxford University neuroscientist Tamar Malkin, however, reveal the opposite. Malkin discovered that victims of phantom pain have stronger rather than weaker brain representations of the missing limb, with no indication of brain remapping. MRI scans of hand amputees and two-handed subjects taken while they were performing other activities, in this case smacking their lips—a testing of the facial region— showed no significant difference in cortex activation in the hand area between the two groups. Malkin concluded that cortical representation of the lips was not taking over areas associated with the missing hand. In addition, lip-smacking movements did not cause pain among the amputees.

    

   These findings shed new light on the neural correlates of the conscious experience of phantom pain,” says Malkin. “We found that the hand area of the brain seems to maintain its originally assigned role, despite the loss of original inputs and outputs,” she adds. “Our results may encourage [new] rehabilitation approaches.”

   Currently, treatment for phantom limb pain includes medication, biofeedback hypnosis, and vibration therapy. Unraveling the mystery of phantom limb syndrome will enable scientists and physicians to develop better methods of treatment for its symptoms.