Impact of Visual Mirror Therapy on Phantom Limb Pain Following Amputation: Visual Responsiveness in Somatomotor Cortex

Abstract

The vast majority of amputees experience phantom limb pain (PLP) in their missing limb. Visual input from mirror therapy has been widely reported to reduce PLP – amputees place a mirror between their missing and intact limbs, and then simultaneously move both the intact and phantom limb while viewing the reflected image of the intact limb moving in the mirror. Investigations in human and non-human primates have suggested that deprivation of somatosensory input can lead to cortical reorganization in the somatosensory cortex, and it has been proposed that PLP may be a consequence of such reorganization. We investigated the impact of visual input on PLP and cortical reorganization in amputees undergoing four weeks of mirror therapy. Eight lower limb amputees and age-matched controls completed three fMRI scans at two weeks intervals. After the first scan session (baseline), amputees began 15 minute daily sessions of mirror therapy and recorded their daily pain experiences. During each scan session, we measured activation elicited by visual presentation of limbs corresponding to the intact and amputated limb. We also measured somatomotor activation for the intact and amputated limb as well as adjacent body regions. Consistent with prior reports, we found a reduction in PLP with mirror therapy. Further, we observed differences in visually elicited activations that were modulated over the course of the mirror therapy. Visual presentation of a foot corresponding to the amputated limb (but not hands or a foot corresponding to the intact limb) produced stronger activation of somatomotor cortex than in controls, and the strength of this activation diminished following therapy. These results suggest that removal of somatosensory input due to limb amputation unmasks visual responses in somatosensory regions, which may contribute to or be a marker for PLP, and that mirror therapy helps to reverse these changes.

Meeting abstract presented at VSS 2013