Reorganization of motor and somatosensory cortex in upper extremity amputees with phantom limb pain

Phantom limb pain (PLP) in amputees is associated with reorganizational cha nges in the somatosensory system. To investigate the relationship between s omatosensory and motor reorganization and phantom limb pain, we used focal transcranial magnetic stimulation (TMS) of the motor cortex and neuroelectr ic source imaging of the somatosensory cortex (SI) in patients with and wit hout phantom limb pain. For transcranial magnetic stimulation, recordings w ere made bilaterally from the biceps brachii, zygomaticus, and depressor la bii inferioris muscles. Neuroelectric source imaging of the EEG was obtaine d after somatosensory stimulation of the skin overlying face and hand. Pati ents with phantom limb pain had larger motor- evoked potentials from the bi ceps brachii, and the map of outputs was larger for muscles on the amputate d side compared with the intact side. The optimal scalp positions for stimu lation of the zygomaticus and depressor labii inferioris muscles were displ aced significantly more medially (toward the missing hand representation) i n patients with phantom limb pain only. Neuroelectric source imaging reveal ed a similar medial displacement of the dipole center for face stimulation in patients with phantom limb pain. There was a high correlation between th e magnitude of the shift of the cortical representation of the mouth into t he hand area in motor and somatosensory cortex and phantom limb pain. These results show enhanced plasticity in both the motor and somatosensory domai ns in amputees with phantom limb pain.