We spend a lot of time looking in the mirror at ourselves on a daily basis. We are able to watch ourselves do activities by looking in a mirror, like putting on makeup. We are able to see exactly what we are doing. Mirror therapy is when a person would watch the mirror reflection of normal hand movements. Research shows that a big part of improving motor learning and making motor control easier is watching normal movement. Motor learning is improving motor skills, like hand movements, and motor control how we perform motor skills and control movement. When a person has a stroke, it means that blood travelling to their brain stops or slows down. This means that no oxygen or nutrients that the brain needs to function do not reach the brain. People who have had a stroke may experience paretic arm movements. Paretic arm movement means the person have trouble moving their arm and it may be weak due to slight paralysis.
A potential explanation for mirror therapy is the mirror neuron system in the brain. The mirror neuron system includes many areas of the brain, including the inferior prefrontal gyrus (important for understanding speech and expressing what you want to say), the inferior parietal lobule (important for understanding facial expressions and understanding sensory information), the superior temporal sulcus (important for aspects of social cognition), and the premotor cortex (important for motor function). The mirror neuron system is important for imitation or copying someone’s actions. Imitation is the most common way to learn. It is like playing “monkey see, monkey do” as a child.
To study the effects of mirror therapy, Chia-Hsiung Cheng (2017) conducted two experiments. The participants were 16 young adults (all between the ages of 20 and 24 years old). They were all right-handed and healthy with no history mental disorders. In one of the experiments, the researcher looked at the effects of observing hand movements that were normal and hand movements that were not normal on the somatosensory system. This system in the brain is involved in the perception of the somatic senses, such as touch, pressure, pain, and temperature.
Researchers observed these effects by asking the participant to watch a 4-minute video of a person performing tasks using their normal functioning right hand. The hand movements were smooth and normal. This was the called the normal condition. The abnormal condition was the same, except the hand movements in this video were clumsy and abnormal. The videos were filmed from above the hand, as if the participant was watching their own hand move. Two components used to describe abnormal movements are static and dynamic malformations. Static abnormalities include things like the fingers or thumb are deformed, or the person cannot move their arm or hand very much. Dynamic abnormalities include imperfect movements, such as shaking or tremors. While watching both videos, the participant’s right median nerve (in their right wrist) received electrical stimuli and was asked to relax their hand which was not painful. The researcher recorded the somatosensory evoked fields through the whole experiment.
The results of this experiment showed that observing normal hand movements resulted in much stronger activation of the secondary somatosensory cortex than observing abnormal hand movements. The findings of this research show that observing normal, smooth hand movements is important in mirror therapy. Observing normal hand movements is important in mirror therapy because it causes stronger activation of the motor cortex and somatosensory system than observing abnormal, clumsy hand movements. This can help stroke patients gain back proper, or at least somewhat proper, arm and hand movements.
Cheng, C. H. (2017). Effects of observing normal and abnormal goal-directed hand movements on somatosensory cortical activation. European Journal of Neuroscience, 47(1), 48-57.
