Rehabilitation After Stroke: They do it with Mirrors

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Recent research by Michielsen and colleagues has demonstrated that “mirror therapy”, which can be given at home, results in significant, albeit modest, improvement in arm, wrist and hand movement abilities of stroke patients [1]. Mirror therapy is where the arm with impaired movement is placed behind a mirror and the unimpaired arm is reflected in the mirror, giving the appearance to the patient that when the unimpaired arm is moved, the impaired arm is also moving.

Whilst this sounds like a rather odd description of a slightly disappointing magic trick, this amazing treatment technique, pioneered by V.S. Ramachandran [2], is based on neuroscience. The brain uses multiple sets of information to process body movements: visual information and “somatosensory feedback”, which is a combination of senses of pressure, heat and proprioception (body position). And who said we only had five senses! When damage occurs to the brain, as in stroke, the ability to move may be impaired — if damage is to motor areas (parts of the brain dealing with movement). Rehabilitation may be possible from a neural perspective, as we now know brain tissue to be capable of being reorganised. However, when a stroke patient first tries to move their hand, they see and feel that it does not move. This has an impact on the brain — the neural circuitry is given the message that the movement is not possible. The parts of the brain which are involved in this movement then become inactive over time as they “learn” from the somatosensory feedback that movement is not possible. This prevents rehabilitation of function through what Ramachandran terms “learned paralysis” [3] (this is not to say that the origins of the paralysis are not very real, but that the persistence of paralysis is down to these neural changes).

The mechanisms by which mirror therapy works are not clear, but the logic of mirror therapy is suggested to be as follows: visual stimuli is powerful in the human brain, with large amounts of brain tissue dedicated to it, so if we “trick” the brain into seeing the limb move, it will override the information the brain is getting from the proprioception system that the arm is not moving. The brain areas dedicated to movement for that arm will then be activated, as the system is receiving visual feedback that movement is possible. This overcomes the neural barrier that allows rehabilitation to begin.

Researchers conducted a study to explore this technique with stroke patients [1]. Patients were allocated to either the mirror therapy or control group. All patients completed a 6-week training program, performing physical exercises with their arms, hands and wrists. All patients attended a rehabilitation centre once a week for a session with the physiotherapist and then were asked to practice at home for one hour, 5 times a week. Participants kept a diary of their exercises and received telephone calls to support them. The only difference between the two groups was that the control group had a normal view of both of their arms, whilst the mirror therapy group saw their unaffected arm reflected where they would normally view their affected arm. Data were collected from all patients relating to movement, including the force of grip, performance on tasks to lift, pinch and move and electro-physiological responses to guage muscle activation. Additionally, a sub-sample underwent fMRI scanning before and after the intervention.

Comparing the movement data, participants in the mirror therapy group performed significantly better than those in the control group. Remember: both groups did the same procedure of exercise, the different was the view they had. These results suggest that mirror therapy works to improve movement in stroke patients. Great, but how? The fMRI data found that in the mirror therapy patients, brain activity was increased in the motor area in the damaged side of the side. Prior to the therapy, the activity in the brain’s motor areas was unbalanced, with high activity in the undamaged side of the brain. The mirror therapy seemed to restore this balance, so the motor areas in both sides of the brain were activated. This suggests that the mirror therapy is causing some reorganisation in the brain tissue.

The study is limited by a relatively small sample size (20 participants in each group). fMIR data was collected from only 9 mirror therapy patients and 7 control group patients. Further research is required to understand the neuronal mechanisms: greater attention to motor task might be increasing the brain activity, “mirror neurons” may be activated and play some role and the precise neural pathways are unknown. More work is also required to understand how much mirror therapy is necessary (how many sessions? For how long?) and whether there are participants for whom this therapy is more or less effective.

Nevertheless, the study provides us with a very concrete example of how research into the brain can have practical applications. Neuroscience is highly complex and can appear quite esoteric and abstract. However, the logic underlying neuroscience studies is often easily understood and the findings may be directly applicable to health care. Research into the brain has shown us that the brain structure remains “plastic” (neuroscience jargon to mean it can be altered) and provides hope for those affected by damage to the brain.

References

1. Michielsen et al. Motor Recovery and Cortical Reorganization After Mirror Therapy in Chronic Stroke Patients: A Phase II Randomized Controlled Trial. Neurorehabil Neural Repair. 2011 Mar;25(3):223-33. Epub 2010 Nov 4.
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2. Ramachandran et al. Touching the phantom limb. Nature. 1995 Oct 12;377(6549):489-90. No abstract available.
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3. Ramachandran VS & Blakeslee S. Phantoms in the Brain: Probing the Mysteries of the Human Mind. William Morrow & Company. 1998