Phantom limb pain, cortical reorganization and the therapeutic effect of mental imagery

Abstract

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.

Interactions between Pain and the Motor Cortex: Insights from Research on Phantom Limb Pain and Complex Regional Pain Syndrome

“…83 Another fMRI study focused on cortical reorganization within primary motor and somatosensory cortices prior to and after mental-imagery training that included movements of the phantom limb. 60 After training, the reduction in constant pain scores co-varied significantly with the decreased activation of the contralateral hand/ arm area within the motor cortex during a lip-purse movement, indicating a reversal of the presumably maladaptive motor reorganization. Patients also reported improvement in freedom of movement of the phantom limb as training progressed.…”

“…Evidence to the contrary comes from neuro-imaging studies, whose findings generally support the existence of a relationship between phantom limb pain and the spatial extent of amputation-induced reorganization in the motor cortex, this reorganization being characterized as a medial shift of the face muscle representation in upper-limb amputees (i.e., displacement toward the former hand area). 37,[58][59][60] As these studies have shown that more reorganization is associated with more pain, this reorganization induced by amputation is generally considered an example of maladaptive plasticity. Taken together, the results of studies using EMG, TMS, and other neuro-imaging techniques suggest the existence of some relationship between motor reorganization and pain after amputation, but the exact nature of this relationship remains unclear.…”

Phantom percepts: Tinnitus and pain as persisting aversive memory networks

“…Similarly, animal (19) and human data (20) demonstrate that cortical map plasticity in the auditory cortex is associated with tinnitus and that the more pronounced the reorganization is, the more severe the tinnitus is perceived (20). Furthermore, these remapping changes normalize when the pain (21) or the tinnitus improves (22). Topographic development and reorganization in all sensory areas of adult cortex are governed by similar/common mechanisms of synaptic plasticity (23), likely explaining the analogy between phantom pain and tinnitus.…”

Neuropathic Pain Post Spinal Cord Injury Part 1: Systematic Review of Physical and Behavioral Treatment

“…Visual imagery is a unique method of therapy that has been used for maintaining skill during recovery from a sports injury, reducing phantom limb pain, and developing empathy and for injuries requiring rehabilitation. [38][39][40] The use of mental imagery by people with SCI stimulates activation in the motor cortex, as well as in individuals without SCI. 41 Visual imagery appears to be particularly useful for patients with cauda equina injuries.…”