Mirror box

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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.

In a 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.

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.

Ramachandran's theory was challenged by a 2010 research study conducted by Marian Michielsen of the University Medical Center, Rotterdam. Michielsen carried out research involving 22 stroke victims which suggests that mirror therapy works by enhancing the spatial coupling between limbs. Michielsen stated that "The hypothesis that the mirror illusion enhances spatial coupling is supported by studies on healthy volunteers, showing that the mirror illusion increased the tendency of one limb to take on the spatial properties of the other limb.(Michielsen et al. 2010)

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[edit]

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)

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