Vol. 24 Issue 5
Learning by Imitation
The mirror neuron system has implications for neurorehab
Dr. Giacomo Rizzolatti of the department of neuroscience at the University of Parma, Italy, describes mirror neurons as "a special class of brain cells reflecting the outside world and revealing a new avenue for human understanding, connecting, and learning."1
The mirror neuron system (MNS), referred to popularly as the "monkey see, monkey do" system, was first discovered in the early 1990s in premotor area F5 of the macaque monkey.1 The name refers to the imitative motor actions the monkey performs when it observes another monkey or human making hand or mouth movements. Work by Strafella,2 Buccino,2 Iacoboni,4,5 and colleagues confirmed the presence of a MNS in humans.
The MNS in humans, a neuronal mechanism that matches both observation and execution of movement,6 is thought to also be involved in higher cognitive processes, such as an individual's being able to imitate and learn from others' actions, to understand their intentions, and to empathize with their pain.4,7,8
Motor imagery harnesses both visual and motor circuits, depending upon the type of imagery performed; it also plays an important role in the development of motor skills. Transcranial magnetic stimulation (TMS) studies indicate that the muscles involved in the observed or imaged action exhibit changes in corticospinal excitability.2,9 Recent studies link the absence of a mirror neuron system to autistic spectrum disorder.10-13
About 15 percent of mirror neurons, audio-visual mirror neurons, respond to the sound associated with the movement. For example, they fire at the sound of a cracking peanut, tearing paper, turning of a doorknob, etc.14-17 These audio-visual motor neurons might be connected with our ability to plan and carry out actions and to recognize the actions of others. They might also be associated with gestural communication.18
Evidence from neurophysiological and brain imaging studies indicates neuronal activity in the brain predominantly involving the ventral pre-motor cortex and the inferior parietal cortex.2,8,9 Evidence exists that, as with mental imagery, action observation also involves increases in respiration rate, again suggesting activation of central control mechanisms related to motorically executed actions.19 Work by Stefan, et al. proposed that the MNS is instrumental in motor learning,20 and that overt motor practice is not necessary for implicit motor learning.21 Observation of even simple movements may facilitate motor performance.20-21
How It Works
You are watching a movie and in one scene an intruder smashes a lamp on a woman's head. You immediately recoil in sympathyindicating an active mirror neuron system.
When you lunch with a friend and she picks up her fork, you know what this infers because your brain mirrors the sequence.
Jane observes as Roberta grasps a bottle of water and raises it to her mouth. We call this action-observation. Now Jane repeats the same actionshe grasps the bottle of water and raises it to her mouth. We refer to this as observation-execution. The same visual motor neurons fire during action-observation and during observation-execution.
In another scenario, Jane smiles at Roberta and picks up a bottle of water. Roberta understands immediately that Jane's intent is to hand her the water. When the MNS is dysfunctional (as is possibly the case with autism), the observer lacks the ability to comprehend and respond appropriately to another's behavior.11
Imitation plays an important role in human development. Motor imitation implies motor imagery.23 Motor imagery refers to the mental rehearsal or "act of cognitively reproducing simple or complex motor acts without corresponding motor output."24-28
Athletes, musicians and surgeons have long used motor imagery to improve -performance, and there is growing evidence that the technique can be an effective therapeutic tool for treatment of patients with neurological conditions.27,29-33 Both motor imagery, an essential part of motor imitation, and motor execution increase the excitability of the corticospinal pathway. Both involve covert actionsthat is, action that is simulated (motor imagery and action observation) but not executed.34 Because motor imitation incorporates motor imagery, the additional motor components in imitation (observation and execution) might intensify its therapeutic value.23
Buccino and colleagues23 point out that motor imitation encourages the use of whole movements rather than breaking them down into small components, as is often the case in rehabilitation therapy and, in fact, is often suggested as part of the treatment plan. We know from the motor-learning literature that, in most instances, whole practice is the preferred mode for learning and retention.35-36
For instance, rather than having the patient practice grasping the telephone and replacing it on the receiver repetitively until the skill is mastered, and then in the next session have him/her practice dialing and speaking into the phone, the patient would practice the entire task during the same treatment session
Neurologically impaired patients can better learn some complex actions by initially practicing the transitional states or elementary components before moving to the whole task.
Thus far the evidence, albeit limited, suggests that action observation/observation execution (motor imitation) might be a viable complement to more traditional treatment.
Results of Dr. Buccino's recent study with stroke patients at the University of Parma37 hold promise.
The experimental group consisted of eight stroke patients (six months post stroke) with moderate paresis of the contralateral upper extremity. All had undergone intensive therapy prior to the study. During the rehabilitation sessions of action observation therapy, patients in the experimental group sat relaxed in a chair with their arms positioned on a table. They watched video sequences of hand and arm actions involving tasks of daily living on a large TV screen, followed by repetitive practice of the actions they had observed.
After viewing the video sequence for six minutes, the patients performed the observed action for six minutes with their paretic arms, using the same objects shown in the video. Researchers presented each action twice during the training. A psychologist ensured that patients remained attentive to the video while not moving their hands and arms.
Each therapy session lasted 90 minutes, and patients underwent 18 sessions on 18 consecutive days. The researchers showed 54 video sequences over the study course, with tasks moving from simple to more complex actions.
The control group matched the experimental group, except they viewed sequences of geometric symbols and letters. They were deliberately shown non-object, non-moving pictures so as not to activate the mirror neuron system. Later, a therapist guided them in practicing the same hand/arm actions performed by the experimental group. Additionally, all participants underwent functional magnetic resonance imaging (fMRI) before and after treatment and performed a task of manually exploring objects with each hand during the scanning.
Outcomes from standard functional motor assessments and patients' self-reports demonstrated that a rehabilitation program consisting of action observation with intensive repetitive practice of the observed actions provided a significant improvement of motor functions in stroke patients with upper-extremity weakness. The control group of patients did not show such an improvement.
Secondly, fMRI results from the experimental group revealed increased activation in areas involving the action observation/action execution systemthe bilateral ventral premotor and the inferior parietal areas or the MNS37indicating this system might play a significant role in motor learning and motor recovery.
While the activity used in this study (manual exploration of objects) did not constitute the action observation/action execution used in the video therapy, it did demonstrate activation of the MNS as an effect of the therapy. The positive outcome lasted up to eight weeks after treatment.37 Currently, Buccino is conducting a multi-center study using action observation therapy with patients diagnosed with Parkinson disease.
Using TMS, Clark and colleagues38 recorded motor-evoked potentials (MEP) in the first dorsal interosseous muscles in normal subjects under various conditions including observation, (mental) imagery and imitation. Action imitation produced the greatest MEP facilitation, consistent with an increase in excitability at the cortical and spinal level. When subjects both observed and imagined the hand action, MEPs in the first dorsal interosseous muscles were facilitated, though less so than during action imitation.
The subjects simulated the action internally, during both action observation and action imagined (mental imagery), which is consistent with Jeannerod's motor simulation theory.34 The similarities between observation and imagery in terms of corticospinal activation illustrates the congruence between the two methods.38
Therapists can use both of these techniques as an adjunct to physical activity to promote motor-skill learning in patients with neurological conditions, including stroke, Parkinson disease, multiple sclerosis and amyotrophic lateral sclerosis. (For details on the use of mental imagery see, "Harness the Power of the Mind: Mental Imagery as a Therapeutic Tool," Advance for Occupational Therapy Practitioners, July 24, 2006, 22:40-44.)
References available at www.advanceweb.com/OT or upon request.
Marilyn Trail, MOT, OTR, is co-associate director of education on Parkinson research at the Michael E. DeBakey VA Medical Center's education and clinical center, and is an assistant professor of neurology at Baylor College of Medicine, Baylor, Texas.
Using Action Observation Therapy with Neuro Patients
o date, there are no protocols for initiating action observation interventions for use in rehabilitation. The following are suggestions based upon a review of the literature on the mirror neuron system, mental imagery and rehabilitation, and learning.
Choose a patient who is alert and able to follow instructions.
Choose a functional task that involves activities of daily living (e.g., grasping a cup or other object).
Have the task involve the hand/arm.
Begin with a task or action familiar to the patient, "overlearned" movements. Move from simple to the more complex. Demonstrate / present the task or activity correctly.
You also could have the patient watch a video/DVD of the task, then observe you performing it, or have the patient look at pictures of the task, with each picture showing a task component, and/or have the patient hear the sound of the task.
Action observation as well as mental imagery can be embedded in the occupational therapy intervention. Practice of the action or task is necessary for learning. Distributed practice as compared to massed practice enhances acquisition and learning of motor skills.
Do not deliver feedback too exact, too fast or too often. However, feedback frequency may need to be increased for more complex tasks or actions and in the early learning stage.