I. Overview
Motor imagery therapy (mental practice, mental imagery) refers to repeated motor imagery performed to improve motor function without any motor output, activating a specific area of an activity in the brain based on motor memory, thus achieving improved motor function.
As early as the 1930s, scholars found that imagining doing a certain type of movement could improve the functional level of simple movements. Later studies applied motor imagery to the field of sports psychology. In the field of sports, the main purpose of motor imagery therapy is to improve specific motor skills. Researchers often divide study subjects into 3 or 4 groups: a control group without any treatment; at least 2 observation groups (one group receiving motor imagery therapy and one group performing somatic movements); and an additional observation group receiving a combination of motor imagery therapy and somatic movements.Brouzivne et al. studied the effects of motor imagery plus somatic exercises on the stroke technique of novice golfers. They divided 23 volunteers (novice golfers) from a university physical education department into three groups: group 1 consisted of physical practice plus motor imagery, group 2 consisted of physical practice alone, and group 3 engaged in other physical activities. It was found that the students in group 1 had better batting skills than those in group 2, suggesting that motor imagery can enable beginners to acquire new skills. Thus, it can be seen that sports imagery therapy has been used for more than half a century, but mainly in the field of sports psychology. Rehabilitation Center of the First Affiliated Hospital of Henan College of Traditional Chinese Medicine, Huadong
In 1950 Hossack introduced the concept of mental imagery, which is a reaction (experience) similar to that produced by the stimulation of receptors when the senses are not stimulated accordingly, with the involvement of the central nervous system. Mental imagery, also called imagination or mental presentation, is often a reshaping of previous conscious experience and has a certain predictability that occupies an important place in memory and motivation. It also plays a large part in visuospatial reasoning and invention. Motor imagery has been proposed later, but without a clear definition. decety considers motor imagery as a state representing a specific motor function that is intrinsically reactivated in working memory without any apparent motor output and follows the principles of central motor control. Others consider motor imagery (mental imagery, mental practice mental training) to be the repeated internal (cognitively) simulation and rehearsal of motor activity without any apparent physical activity.
The combination of motor imagery and physical exercise has been reported to improve muscle strength, endurance, and precision of movement, facilitate the learning of sports or new skills, improve balance in older women, correct the posture of patients with abnormal spinal curvature, and enhance mobility, etc. In the late 1980s and early 1990s, motor imagery techniques In the late 1980s and early 1990s, motor imagery techniques began to be gradually applied to functional training. Recent studies have found that motor imagery can also improve the motor function of stroke patients with hemiplegia, as a means of activating the motor network, and as an “alternative” treatment that can be applied at any stage of stroke. It is not dependent on the patient’s residual function and is closely related to the patient’s active movement.
However, brain damage can interfere with normal motor imagery. In stroke patients, the site of the lesion can affect two factors of motor imagery therapy, namely accuracy and timeliness. For example, patients with parietal lobe damage, which is responsible for generating and retaining motor patterns, may be affected by the accuracy of motor imagery therapy; interference with the primary motor cortex may prolong the response time to motor imagery; and damage to the parietal or frontal lobes may also affect the accuracy and timeliness of motor imagery. Post-stroke patients still have some motor imagery ability, but accuracy and timeliness are affected, i.e., chaotic motor imagery, which manifests as the inability to perform accurate motor imagery. Alternatively, precise motor imagery can be performed but not in time.
Theoretical study of the mechanism of action
Although some studies have found an overlap of functional activity areas between actual movement and “motor imagery”, both have their own dominant functional activity areas. The most powerful explanation for the improvement of motor learning by “motor imagery” therapy remains the psychoneuromuscular theory (PM theory), which is based on the idea that the individual’s central nervous system has stored motor plans or “flow charts” (flowcharts) for performing exercise. “It is assumed that the motor “flowchart” involved in the actual activity can be reinforced and refined during the “motor imagination” because Imagination involves the same motor “flowchart” as the actual movement. Imagery helps to learn or complete activities by improving coordination patterns in the formation of motor skills and by giving muscles additional opportunities to practice skills.
The motor “flow chart” may be intact or partially present in a brain-injured person despite physical dysfunction. In any random movement, the idea of movement is always present in the brain before the excitatory impulses are transmitted until movement occurs. One of the roles of rehabilitation is to repeatedly reinforce this normal movement pattern from the brain to the muscle groups, and motor imagery is more effective in promoting the reinforcement of this normal motor transmission pathway. Early application of motor imagery can enhance the input of sensory information, promote the activation of latent pathways and dormant synapses, accelerate the reperfusion of the ischemic semidark zone and the improvement of cerebral blood flow, and reduce the degree of neurological impairment, which, together with other treatments, can improve the effectiveness of rehabilitation and reduce the degree of disability in stroke. In patients with complete paralysis, motor imagery can lead to the repair or reconstruction of damaged motor conduction pathways, which supports the theory that some dormant synapses can awaken and play a compensatory role after central nerve injury, and their threshold decreases with frequent use. Compared with passive movement of the limb, motor imagery may be more consistent with the normal pattern of excitation transmission from the brain to the limb, and thus more effective in promoting the formation of normal motor reflex arcs.
Clinical research findings and status of motor imagery therapy
(A) Application of motor imagery therapy in healthy people
Recent neuroscientific studies have shown that the brain areas activated by motor imagery therapy are similar to those activated by the actual exercise. Porro et al. used functional magnetic resonance imaging (fMRI) to study the metabolic activity of the brain. The study by Porro et al. using functional magnetic resonance imaging (fMRI) found that imagining finger-to-finger movements activated the primary motor area (M1) to a greater extent than visual imagery alone, but to a lesser extent than actual finger-to-finger movements. The study also found that imagining finger-to-finger movements also activated primary sensory cortices (S1), but to a lesser extent than visual imagery alone.
Using fMRI, Gerardin et al. found that imagined finger movements activated bilateral premotor areas and the parietal, basal, and cerebellar nuclei compared with actual finger movements in the resting state. Compared with actual finger movements, imagined finger movements activated more bilateral premotor areas, prefrontal areas, supplementary motor areas, ipsilateral posterior parietal areas, and caudate nuclei. They suggest that motor imagery activates more anterior frontal and posterior parietal areas than actual movement.
Motor imagery can cause changes in cortical representation areas as well as actual movement. Because of the similarities in activation of cortical areas and neurophysiology, motor imagery can influence actual movement. Studies in healthy populations have shown that motor imagery can increase muscle strength and improve executive ability. A meta-analysis showed that motor imagery can improve motor skills, and the degree of improvement was related to the type of task, previous experience, and duration of training.
(B) Application of motor imagery therapy in stroke rehabilitation
Since the 1990s, motor imagery therapy has been applied to stroke patients based on neuroimaging findings, and has become a hot topic of research in stroke rehabilitation in recent years.
Stevens et al. studied the efficacy of imagining wrist movements and functional activities in two patients recovering from stroke hemiplegia. They asked the patients to imagine wrist extension, forearm rotation forward and backward, and used a mirror box apparatus to imagine the functional activities of objects and manipulated objects. Page et al. studied the efficacy of motor imagery therapy using a randomized, double-blind control method. 32 patients with chronic stroke and moderate stroke were found to have improved upper limb scores, improved joint mobility, and reduced work time. Thirty-two patients with chronic stroke with moderate hemiparesis received 30 min of training twice a week for 6 weeks, focusing on activities of daily living (ADLs). 32 patients were randomly divided into observation and control groups, with the observation group receiving 30 min of motor imagery training after somatic training and the control group receiving 30 min of relaxation after the same somatic training as the observation group. The upper limb movement research arm test and the Fugl-Meyer upper limb section were used for evaluation. The results found that patients who received imagery therapy had significantly improved upper limb function and acquired new ADL function.Liu et al. studied the efficacy of motor imagery therapy in stroke patients using a randomized controlled approach. They selected 46 patients over 60 years of age with cerebral infarction and randomly divided the patients into 2 groups. One group received 15 sessions (1 session/d for 3 weeks) of ADL motor imagery therapy training and the other group received 15 sessions (1 session/d for 3 weeks) of regular ADL training. The assessment methods included 15 trained and 5 untrained tasks, the Fugl-Meyer motor function scale, and the Color Trails Test. The results showed that patients who received motor imagery therapy were more able to perform both the trained and untrained tasks than those who received conventional ADL training, and that this ability was maintained after the training session. Malouin et al. studied the effect of motor imagery therapy on two mobile tasks in stroke patients, and by imagining two tasks, standing and sitting, the patient’s weight-bearing capacity on the hemiplegic side increased significantly, and this effect lasted for 24 h.
Stimulation plays an important role in the reorganization of neurological functions after adult brain injury, and motor imagery is an internal motor stimulus. By event-related functional fMRI, Johnson-Frey found that the anterior motor area, parietal lobe, and motor cortex of the contralateral limb of the paralyzed limb were activated after motor imagery in l patients with severe hemiparesis after stroke.
Sirigu et al. found that motor imagery was also impaired in patients with parietal lobe damage compared with controls and one patient with primary motor cortical damage, suggesting that the parietal lobe has an important loop related to imagery. Schwoebel et al. found that damage to the frontal and/or dorsolateral parietal lobes was more likely to lead to impaired motor imagery than damage to other parts of the brain.
Kimberley et al. used fMRI to observe cortical activation after imagining wrist movements in patients with severe hemiplegia and found that motor imagery in healthy controls was controlled by the contralateral brain, whereas motor imagery in stroke patients mainly activated the contralateral primary sensory area, the ipsilateral primary motor area, and the ipsilateral supplementary motor area. The ipsilateral supplementary motor area is activated. The percentage change in the intensity of ipsilateral brain signals during motor imagery was greater in stroke patients than in healthy subjects.
In summary, the use of motor imagery therapy in stroke patients has been shown to be effective. Similar to the brain regions activated by actual exercise, motor imagery therapy is an internal stimulation of the brain that promotes functional reorganization after brain injury.
IV. Assessment of motor imagery ability
Before performing motor imagery therapy, the patient’s motor imagery ability should be evaluated first. There are several assessment methods, one of which is kinesthetic and visual imagery questionnaine (KVIQ). The KVIQ is a modified version of the Movement Imagery Questionnaire (MIQ), which classifies the kinesthetic and visual components of each of the 10 postures into 5 levels. The motor postures used include head movements (flexion and extension), shoulder movements (elevation), trunk movements (flexion), upper extremity movements (shoulder flexion, elbow flexion and extension, opposable fingers), and lower extremity movements (knee extension, hip abduction, hip internal rotation, and foot tapping on the ground). Subjects were required to actually perform these exercises and then immediately imagine doing the same exercises. The subjects rated their induced motor imagery ability (on a 5-point scale, with 1 being low imagination and 5 being high imagination) based on 2 methods [one method rated the clarity of the imagery (visual rating); the other method rated the extent of perceived motion (kinesthetic rating)].
Another method of assessing motor imagery ability is the motor imagery screening test (MIST). Participants were asked to imagine a step movement (i.e., taking a step of 3 cm in height and then going down the step) and to speak it orally each time they went up the step until the rater called it off. The duration of each trial varied (25, l5, 35 s, randomized). The subject was then asked to perform the actual step movement for the same amount of time. In addition to recording the number of steps, the time of each step was also recorded with a stopwatch so that the imagined step movements could be compared with the actual step movements. The test was performed on the non-paralyzed side of the lower extremity, and the imagined movement was performed before the actual movement.
Since motor imagery may also be impaired after brain injury, motor imagery should be evaluated before performing motor imagery therapy.
V. Clinical application of motor imagery therapy
(I) Indications
“Many studies have not described the subjects in detail, and the inclusion and exclusion criteria are different, which is a major problem in the clinical application.
The selection of patients and the implementation of treatment should be considered in the following aspects: ① Patients should have certain imaginative abilities. There are three commonly used tools to assess motor imagery, namely the movement imagery questionnaire (MIQ), the vividness of motor imagery questionnaire (VMIQ) and the kinesthetic and visual imagery questionnaire (KVIQ). Both the MIQ and VMIQ have modified versions, and the newer assessment method, the KVIQ, has been validated for healthy and disabled subjects. The controllability of motor imagery scale is a commonly used alternative assessment method. ②Task variety and familiarity. Familiarity is a prerequisite for the successful use of motor imagery therapy, and the deeper the patient’s experience with an activity, the more effective the “motor imagery” therapy will be. (iii) Working memory. It includes the complex procedures for storing and processing information, and can be divided into visual, verbal, and musculo-motor memory, etc. The completeness of working memory has an important impact on the effectiveness of therapy. ④Motivation. Patients with high motivation and low anxiety have better motor imagery efficacy, and the treatment itself can increase patients’ motivation and self-confidence; therefore, patients with low motivation and higher anxiety should be encouraged to join and should not be excluded. ⑤ Adherence. Although several methods of assessing adherence have emerged, there is no validated assessment tool to exclude nonadherent patients.
In practical application, patients are also required to be able to understand the instructional language, so it has been suggested that patients with obvious intellectual impairment, sensory aphasia and those who cannot perform motor imagery (MIQ rating score <25) should be excluded from the treatment, as well as those with confused motor imagery and those with poor adherence should be attempted to be excluded, etc.
Heart rate and respiratory rate are increased during exercise imagination and actual execution of exercise, and the exercise completion time is also very close under normal conditions. Therefore, there are two other ways to initially determine whether exercise imagery therapy is applicable in clinical practice: ① Changes in autonomic regulation. The therapist can make a simple assessment based on the degree of increase in heart rate or respiratory rate when the patient imagines the therapy: ② Mental chronometry. This is assessed by the difference between the imagined movement and the actual physical movement completion time, but this method has more limitations and controversies.
(II) Training procedures and considerations
Jackson et al. suggested that motor imagery and traditional functional training must be used together, but motor imagery is only used as an adjunctive method. Implementation usually consists of 6 operational steps: description of the task, pre-training, motor imagery, repetition, problem solving, and practical application.
Although motor imagery training does not require the presence of activity, in practice, patients who are good or eager to recover keep imagining the movement of their limbs, which may lead to anxiety or increased spasticity, and may also artificially mix in unnecessary factors. Therefore, activation activities for compliance in stroke patients should be simple and should be completed in as short a time as possible, while strengthening supervision and guidance of the patient’s exercises and urging the patient to pay attention to rest. It is more difficult to perform for those with poor compliance, but it is an effective tool.
The following four influencing factors need to be considered in the specific implementation of motor imagery therapy: inability to implement motor imagery correctly or with insufficient accuracy: poor compliance; use of alternative methods, such as visual imagery, but no objective assessment method has been proposed for detection; inability to inhibit actual movement, some methods can be used to monitor the appearance of various visible or hidden movements during training, such as the application of electromyography, etc.
(C) Operation methods
The design of motor imagery program varies from person to person, and there are different motor imagery models for different training goals, and there are various contents and methods, but a standardized program to guide clinical treatment has not been proposed yet. At present, it is believed that the “imaginary” activities should be selected from the functional training activities in a targeted manner, and can be implemented in combination with computer technology. The duration of motor imagery therapy should be shorter than that of physical therapy, which is generally 12-15 min.
The general operation is after each functional training session. The patient is moved to a quiet room to listen to a 10-minute tape of “motor imagery” instructions (the first two sessions can be accompanied by someone). The patient lies on his back with his eyes closed and spends 2-3 min relaxing his whole body. The patient is instructed to imagine lying in a warm, relaxed place and is asked to alternately tense and relax the muscles of the feet, followed by the legs, upper extremities and hands. The patient is then prompted to perform intermittent “motor imagery” for 5-7 min, which should focus on one or more activities to improve a function, while emphasizing the patient’s use of all of his or her senses. In the last 2 min, the patient is told to refocus on his or her body and surroundings, told to return to the room, let him or her experience the sensations of the body, and then let him or her listen to the sounds around him or her, and finally the narrator counts backwards from 10 to 1, and opens the patient’s eyes when he or she reaches 1.
In the patient’s functional training, skill learning begins with the generation of motor ideation, followed by the development of motor pattern control adapted to the needs of the environment. As the patient gains better control and strength over simple activities, direct attention to these activities decreases, so the therapist should be careful to provide appropriate training conditions and should be careful to guide the patient to continuously apply the activity skills learned from a specific rehabilitation setting in other complex and variable settings. Techniques such as motor imagery can be incorporated into occupational therapy to focus on activities of daily living.
Motor imagery therapy can be implemented in three specific ways: listening to recorded instructions, self-regulation, and post-observation practice.
The method used in the study by Page et al. was listening to recorded instructions, and motor imagery training was conducted after PT training in a separate room or at the patient’s home. The motor imagery program was taken from the PT room training program.
Motor imagery exercises were taken from the OT training exercises: functional ADL exercises, i.e., moving blocks, objects and grasping cups, drinking from cups, cooking, shopping, increasing walking speed and symmetry, and ankle joint exercises with the upper limb of the hemiplegic side.
Jackson et al. performed motor imagery therapy training on a stroke patient. The patient was placed in the supine position and performed ankle movements as quickly and accurately as possible, dorsiflexion after hearing a high-pitched (2000 Hz) sound and plantarflexion after hearing a low-pitched (100 Hz) sound. The patient needs to place the foot in a neutral position before the next auditory stimulus can be elicited. After familiarization with the motor movements, the patient was asked to perform a sequence (6 movements) of ankle dorsiflexion and plantarflexion movements (up-down-down-up-down-up). Five sets of movements were done in each session, with each set doing 6 sequences of movements, thus each session included 30 sequences of movements. They were designed with the following instructions: ① assume a comfortable sitting or supine position; ② imagine the movements in the first person as if you were actually doing them; ③ avoid your head and lower limb movements or muscle contractions and stay relaxed; ④ remember to see and feel the movements as if they were actual movements; ⑤ keep your eyes closed while performing a set; ⑥ count the imagined movements (you can use your fingers) and must imagine (6) count the imaginary movements (you can use your fingers), and you must imagine doing 6 sequences of movements in each group; (7) if you are distracted during each group, open your eyes, relax for a moment, and then start from the beginning; (8) remember to do the movements as quickly and accurately as possible.
The specific implementation of motor imagery therapy varies according to the imagination work items, but the treatment must be carried out in a quiet environment and the patient should be in a relaxed state.
(D) Training effect
The clinical application of “motor imagery” therapy in stroke rehabilitation is not much yet, but studies have shown that this therapy can be applied to acute or chronic, mild or severe hemiplegic patients, and is beneficial to improve the patient’s ability to perform hand, ankle, sitting station, activities of daily living (ADL) and functional task relearning (housework, cooking, shopping, etc.). The ability to improve unilateral neglect and other impairments has also been studied in depth for the functional recovery of chronic stroke patients. In recent years, there has been an increase in the number of studies and research on the use of this therapy in stroke rehabilitation.
The role of motor imagery therapy in the rehabilitation of upper limb function in stroke patients is still under further study. For example, Page et al. showed that motor imagery therapy as a special motor technique can activate the same muscle and neural areas as physical therapy training, and the study showed that the treatment group that received motor imagery therapy along with functional training had a new ability to perform meaningful activities, suggesting that functional training combined with motor imagery can improve upper limb function and daily activities in patients with chronic stroke. The results of Zhu Shiwen’s experiment showed that compulsory motor therapy and motor imagery therapy are effective treatments for improving upper limb motor function in patients with brain injury. For those who are eligible for treatment, regardless of whether they are in the recovery or chronic phase, choosing compulsory motor therapy and imagery therapy, especially the combination of the two, is a very effective treatment method that does not require too much medical equipment and is easy to be applied. There are also many studies on the effect of this therapy on the functional rehabilitation of the upper extremities at home and abroad, which occupy a large proportion of the literature in this field.
Malouin et al. found that the combination of imagery and practical training significantly improved the weight-bearing capacity of the lower limbs, and that the improvement in weight-bearing capacity was significantly related to the working memory capacity of the trainees, suggesting that the effect of “motor imagery” is related to the ability to maintain working memory. Dunsky et al. investigated the effect of motor imagery therapy on gait training in the home of stroke patients by subjecting four chronic post-stroke patients to motor imagery therapy during gait training for 3 d per week for 6 weeks, and assessing the patients before, during, and after treatment and at follow-up. The results showed that the patients’ gait length, gait speed, gait frequency and affected side unipedal support time were increased and bipedal support time was decreased, which showed that motor imagery therapy had a facilitating effect on gait recovery in post-stroke hemiplegic patients. Yan Yaning et al. conducted a two-stage crossover study to investigate the effect of combining motor imagery with conventional functional training on the gait recovery of hemiplegic patients by selecting 20 patients with stroke hemiplegia who were stable and had been ill for >6 months. This suggests that the combination of motor imagery with conventional functional training can improve the gait and walking ability of hemiplegic patients in the chronic phase of stroke.
In addition, Wang Gang et al. observed the effect of “motor imagery therapy” on the functional recovery of stroke hemiplegic patients in the recovery period by randomly grouping 60 stroke hemiplegic patients and suggested that “motor imagery therapy” combined with conventional functional training could promote the functional recovery of stroke hemiplegic patients. Compared with the existing rehabilitation treatment methods, it does not increase the investment cost, does not require large treatment equipment, can be trained by patients and family members at home, can reduce the treatment cost, and is easily accepted by patients. There are also some studies in China on the functional effects of motor imagery therapy in combination with other rehabilitation methods. Zhao Wei investigated the rehabilitation methods and efficacy of rehabilitation for stroke patients with hemiplegia and concluded that the combination of electroacupuncture and motor imagery could achieve the best therapeutic effect. Liu Guirong used a combination of motor imagery and passive movement for the early rehabilitation of 70 acute stroke patients. The findings suggest that early rehabilitation can effectively promote the functional recovery of the affected limbs and improve the quality of patients’ survival. Huang Guangying also incorporated the application of motor imagery therapy when observing the effect of early rehabilitation care on secondary injury and ADL in acute stroke patients with hemiplegia.
VI. EXPANSION
Although the efficacy of motor imagery therapy has been clinically verified to some extent, there are some problems and aspects that need to be improved: ① Most of the current literature is about experimental studies and case studies, and most of the explanations about the neurophysiological mechanism of motor imagery therapy are at the hypothesis stage. (2) the sample size of clinical studies is too small, and although there is some experimental evidence of efficacy, it cannot be generalized; (3) the requirements for stroke patients are high, and only patients who are conscious and cooperative can be implemented, so it cannot be applied to all patients; (4) there is a lack of effective outcome assessment and effective testing tools for efficacy, and most of the existing literature still uses joint mobility and muscle strength. (5) The treatment form is single and stays on the surface form, especially on the level of physical stimulation, basically only the therapist speaks the instructional language, and the patient’s active component is not enough; (6) The best time to start the application, the long-term effectiveness, the most suitable patients for this therapy such as severe paralyzed people, etc. There is a lack of systematic research, etc.
The future development can be studied to produce a scale for quantitative evaluation of the efficacy of motor imagery; the method can be combined with computerized techniques such as electromyography and EEG monitoring devices to develop a new type of motor imagery therapy instrument. When conditions are not suitable, light music can be used to soothe patients’ emotions and focus their attention to stimulate motor imagination. There are many similarities between the intentional rehabilitation of TCM and sports imagination, and the organic combination of TCM theory and sports imagination therapy can form an imagination therapy with Chinese characteristics.
Preliminary studies have shown that motor imagery can significantly improve the function of stroke patients with hemiplegia, with the advantages of being highly targeted, easy to learn, and requiring no special equipment; patients and family members can train themselves at home after training, which can better solve the problems of therapists, treatment sites, and financial constraints caused by patients’ functional impairment requiring longer rehabilitation. Overall, there is great potential for the use of motor imagery in post-stroke rehabilitation, and it is worth further research.
Editor: Hua Dong
The First Affiliated Hospital of Henan College of Traditional Chinese Medicine Rehabilitation Center Website: http://www.hnkf.com.cn/