Mirror box
Encyclopedia
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 . 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. Often a phantom limb is painful because it is felt to be stuck in an uncomfortable or unnatural position, and the patient feels they cannot move it.
To retrain the brain, and thereby eliminate the learned paralysis, Ramachandran and Rogers-Ramachandran 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. The use of the mirror box has also been used in the rehabilitation of hemiparesis
, or paralysis one side of the body, due to stroke
and to rehabilition of spatial neglect
.
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." 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."
"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."
Vilayanur S. Ramachandran
Vilayanur Subramanian "Rama" Ramachandran, born 1951, is a neuroscientist known for his work in the fields of behavioral neurology and visual psychophysics...
to help alleviate phantom limb
Phantom limb
A phantom limb is the sensation that an amputated or missing limb is still attached to the body and is moving appropriately with other body parts. 2 out of 3 combat veterans report this feeling. Approximately 60 to 80% of individuals with an amputation experience phantom sensations in their...
pain
Pain
Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."...
, 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
Paralysis
Paralysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. A study conducted by the Christopher & Dana Reeve Foundation, suggests that about 1 in 50 people have been diagnosed...
and painful phantoms if the actual limb had been paralyzed prior to amputation
Amputation
Amputation is the removal of a body extremity by trauma, prolonged constriction, or surgery. As a surgical measure, it is used to control pain or a disease process in the affected limb, such as malignancy or gangrene. In some cases, it is carried out on individuals as a preventative surgery for...
(for example, due to a brachial plexus avulsion
Brachial plexus injury
The brachial plexus is a network of nerves that conducts signals from the spinal cord, which is housed in the spinal canal of the vertebral column , to the shoulder, arm and hand. These nerves originate in the fifth, sixth, seventh and eighth cervical , and first thoracic spinal nerves, and...
), Ramachandran and Rogers-Ramachandran proposed the "learned paralysis" hypothesis of painful phantom limbs . Their hypothesis was that every time the patient attempted to move the paralyzed limb, they received sensory feedback
Feedback
Feedback describes the situation when output from an event or phenomenon in the past will influence an occurrence or occurrences of the same Feedback describes the situation when output from (or information about the result of) an event or phenomenon in the past will influence an occurrence or...
(through vision
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...
and proprioception
Proprioception
Proprioception , from Latin proprius, meaning "one's own" and perception, is the sense of the relative position of neighbouring parts of the body and strength of effort being employed in movement...
) 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. Often a phantom limb is painful because it is felt to be stuck in an uncomfortable or unnatural position, and the patient feels they cannot move it.
To retrain the brain, and thereby eliminate the learned paralysis, Ramachandran and Rogers-Ramachandran 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. The use of the mirror box has also been used in the rehabilitation of hemiparesis
Hemiparesis
Hemiparesis is weakness on one side of the body. It is less severe than hemiplegia - the total paralysis of the arm, leg, and trunk on one side of the body. Thus, the patient can move the impaired side of his body, but with reduced muscular strength....
, or paralysis one side of the body, due to stroke
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
and to rehabilition of spatial neglect
Hemispatial neglect
Hemispatial neglect, also called hemiagnosia, hemineglect, unilateral neglect, spatial neglect, unilateral visual inattention, hemi-inattention or neglect syndrome is a neuropsychological condition in which, after damage to one hemisphere of the brain, a deficit in attention to and awareness of...
.
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." 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."
Is mirror therapy effective?
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 Mosely and Ezendam 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 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."
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 YorkerThe New YorkerThe New Yorker is an American magazine of reportage, commentary, criticism, essays, fiction, satire, cartoons and poetry published by Condé Nast...
article that discusses mirror therapy and its current, and possible future, uses. - Mirror therapy aiding US amputees