Mirror box

A diagrammatic explanation of the mirror box. The patient places the good limb into one side of the box (in this case the right hand) and the amputated limb into the other side. Due to the mirror, the patient sees a reflection of the good hand where the missing limb would be (indicated in lower contrast). The patient thus receives artificial visual feedback that the "resurrected" limb is now moving when they move the good hand. See text for more details.

A mirror box is a box with two mirrors in the center (one facing each way), invented by Vilayanur S. Ramachandran to help alleviate phantom limb pain, in which patients feel they still have a limb after having it amputated.

Based on the observation that phantom limb patients were much more likely to report paralyzed and painful phantoms if the actual limb had been paralyzed prior to amputation (for example, due to a brachial plexus avulsion), Ramachandran and Rogers-Ramachandran proposed the "learned paralysis" hypothesis of painful phantom limbs (Ramachandran & Blakeslee 1998). Their hypothesis was that every time the patient attempted to move the paralyzed limb, they received sensory feedback (through vision and proprioception) that the limb did not move. This feedback stamped itself into the brain circuitry through a process of Hebbian learning, so that, even when the limb was no longer present, the brain had learned that the limb (and subsequent phantom) was paralyzed.

To retrain the brain, and thereby eliminate the learned paralysis, Ramachandran and Rogers-Ramachandran (Ramachandran, Rogers-Ramachandran & Cobb 1995) created the mirror box. The patient places the good limb into one side, and the stump into the other. The patient then looks into the mirror on the side with good limb and makes "mirror symmetric" movements, as a symphony conductor might, or as we do when we clap our hands. Because the subject is seeing the reflected image of the good hand moving, it appears as if the phantom limb is also moving. Through the use of this artificial visual feedback it becomes possible for the patient to "move" the phantom limb, and to unclench it from potentially painful positions.

In 1999 V.S. Ramachandran and Eric Altschuler published the results of pilot studies on the use of mirrors in the treatment of hemispatial neglect (the inability to see or pay attention to one side of observed space) (Ramachandran et al. 1999) and hemiparesis after stoke (muscular weakness on one side of the body).(Altschuler et al. 1999) Ramachandran and Altschuler concluded that mirror therapy may be useful in the treatment of these conditions.

A diagram of a mirror box. A patient inserts their hand into one hole, and their "phantom" into the other. When viewed from an angle, the brain is tricked into seeing two complete hands.

Effectiveness

Although the use of mirror therapy has been shown to be effective in some cases there is still no widely accepted theory of how it works. In a 2010 study of phantom limb pain, Martin Diers and his colleagues found that "In a randomized, controlled trial that used graded motor imagery...and mirror training, patients with complex regional pain syndrome or phantom limb pain showed a decrease in pain as well as an improvement in function post-treatment and at the 6-month follow-up. And it was shown that the order of treatment mattered." However, this study found that mirrored imagery produced no significant cortical activity in patients with phantom limb pain and concluded that "The optimal method to alter pain and brain representation, and the brain mechanisms underlying the effects [of] mirror training or motor imagery, are still unclear." (Diers et al. 2010)

A number of small scale research studies have shown encouraging results, however there is no current consensus as to the effectiveness of mirror therapy. Recent reviews of the published research literature by Moseley (Moseley, Gallace & Spence 2008) and Ezendam (Ezendam, Bongers & Jannink 2009) concluded that much of the evidence supporting mirror therapy is anecdotal or comes from studies that had weak methodological quality. In 2011 a large scale review of the literature on mirror therapy by Rothgangel (Rothgangel et al. 2011) summarized the current research as follows:

For stroke there is a moderate quality of evidence that MT [Mirror Therapy] as an additional intervention improves recovery of arm function, and a low quality of evidence regarding lower limb function and pain after stroke. The quality of evidence in patients with complex regional pain syndrome and phantom limb pain is also low. Firm conclusions could not be drawn. Little is known about which patients are likely to benefit most from MT, and how MT should preferably be applied. Future studies with clear descriptions of intervention protocols should focus on standardized outcome measures and systematically register adverse effects.(Rothgangel et al. 2011)

In 2011 Melita Giummarra and Lorimer Moseley published an article on phantom limb pain that summarized current approaches to treating this problem. They concluded that the benefits of mirror therapy appear to be limited to patients who suffer from cramping and muscular-type phantom pain. They stated:

One randomized controlled trial showed significant treatment effects of mirror therapy ; however, there is limited systematic evidence, and the paradigm appears to be counterproductive during early rehabilitation. Pre-existing body representations or maladaptive cortical reorganization may impede the efficacy of this therapy considering, in a once-off treatment, congenital amputees , and those with chronic phantom pain do not activate contralateral sensory and motor cortices during mirror visual therapy.(Giummarra & Moseley 2011)

See also

• Neuropathic pain
• Phantom limb
• Phantom pain
• Phantom eye syndrome

References

External links

• V.S. Ramachandran's website
• WNYC - Radio Lab: Where Am I? (May 5, 2006) downloadable segment of radio program looks at historical examples and a present-day case of phantom limbs
• Ramachandran's Reith Lecture on Phantom Limbs
• Mirror box therapy web site
• The Itch a The New Yorker article that discusses mirror therapy and its current, and possible future, uses.
• Mirror therapy aiding US amputees