Psychophysical investigations into Ramachandran's mirror visual feedback for phantom limb pain: video-based variants for unilateral and bilateral amputees, and temporal dynamics of paresthesias

摘要

It is widely reported by Ramachandran, Altschuler and others that simple mirror visual feedback can cause phantom sensations in normal observers, and reduce phantom limb pain in amputees. First, a recent experiment designed to replicate classic findings (59 amputees) is reviewed, along with a mirror-based variant developed for bilateral amputees. Then, two variants are described which were intended to intensify effects without eliciting fatigue, and to sometimes reduce phantom pain when the simple mirror is ineffective. The first (simple video feedback) uses a laptop video movie of another (intact) person's limb movement (with metronome-paced periodic movement). The second ("phantom pulse") uses a real-time video image of the observer that flickers between a normal image and a mirror-reversed image at rates varying form 0.5 to 2 cycles/sec (with an 0.2-sec delay). For both conditions, preliminary data from amputees support the finding that movement of one limb causes phantom sensations in the opposite limb, followed by seemingly permanent pain reduction in some amputees. Moreover when normal observers view their movements in these ways, they often report paresthesias, with optimal stimulation occurring in most individuals at 1-2 Hz. Thus psychophysical results may indicate that neural mechanisms underlying mirror visual feedback are temporarily tuned.