MRI explains why amputees can still feel pain in their lost arms

A brain MRI study of upper-limb amputees suggests that phantom pain is a result of preserved structure and function in the former hand area of the sensorimotor complex, contradicting current theories. This scenario has been presented by Tamar Makin from the University of Oxford, and colleagues. in a recent issue of Nature Communications.

The researchers took MRI scans of the brains of 18 single upper-limb amputees and compared them to those of two-handed controls and patients with congenital loss of an upper limb. During the scans, the subjects were asked to move various parts of their bodies, including the fingers of both hands, both arms, the toes and the lips. Amputees who experienced phantom sensations in their lost limb were asked to perform actual movements with their phantoms while those who did not have phantom sensations were asked to imagine moving their missing limbs.

The results showed comparable movement-related activity in the brain when amputees moved their phantom hand and double-handed controls moved their non-dominant hand. The chronic phantom pain of amputees was associated with preserved local functional and structural representations of the missing hand in the brain. However, both acquired and congenital limb absence were associated with reduced inter-hemispheric functional connectivity.

From the results, it appeared that a number of factors interacted to maintain local structural and functional representations in the brain, while modifying long-range connectivity. So, cortical changes following limb amputation are most likely due to a combination of loss of sensory inputs and phantom pain experience, which differs from the accepted model of maladaptive plasticity which suggests that increased phantom pain is associated with increased local reorganization within the brain.