Using functional MRI (fMRI) we investigated 13 upper limb amputees with phantom limb pain (PLP) during hand and lip movement, before and after intensive 6-week training in mental imagery. Prior to training, activation elicited during lip purse showed evidence of cortical reorganization of motor (M1) and somatosensory (S1) cortices, expanding from lip area to hand area, which correlated with pain scores. In addition, during imagined movement of the phantom hand, and executed movement of the intact hand, group maps demonstrated activation not only in bilateral M1 and S1 hand area, but also lip area, showing a two-way process of reorganization. In healthy participants, activation during lip purse and imagined and executed movement of the non-dominant hand was confined to the respective cortical representation areas only. Following training, patients reported a significant reduction in intensity and unpleasantness of constant pain and exacerbations, with a corresponding elimination of cortical reorganization. Post hoc analyses showed that intensity of constant pain, but not exacerbations, correlated with reduction in cortical reorganization. The results of this study add to our current understanding of the pathophysiology of PLP, underlining the reversibility of neuroplastic changes in this patient population while offering a novel, simple method of pain relief.

Why only certain patients develop debilitating pain after spinal chord injury and whether structural brain changes are implicated remain unknown. The aim of this study was to determine if patients with chronic, neuropathic below-level pain have specific cerebral changes compared to those who remain pain-free. Voxel-based morphometry of high resolution, T1-weighted images was performed on three subject groups comprising patients with pain (SCI-P, n = 18), patients without pain (SCI-N, n = 12) and age- and sex-matched controls (n = 18). The SCI-P group was first compared directly with the SCI-N group and then subsequently with controls. Overall, grey and white matter changes dependent on the presence of pain were revealed. Significant changes were found within the somatosensory cortex and also in corticospinal tracts and visual-processing areas. When the SCI-P group was directly compared with the SCI-N group, reduced grey matter volume was found in the deafferented leg area of the somatosensory cortex bilaterally. This region negatively correlated with pain intensity. Relative to controls, grey matter in this paracentral primary sensory cortex was decreased in SCI-P but conversely increased in SCI-N. When compared with controls, discrepant corticospinal tract white matter reductions were found in SCI-P and in SCI-N. In the visual cortex, SCI-N showed increased grey matter, whilst the SCI-N showed reduced white matter. In conclusion, structural changes in SCI are related to the presence and degree of below-level pain and involve but are not limited to the sensorimotor cortices. Pain-related structural plasticity may hold clinical implications for the prevention and management of refractory neuropathic pain.

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