Working memory and mental practice outcomes after stroke

Practical research-based guidance for motor imagery practice in neurorehabilitation

PURPOSE

The purpose of this appraisal is to offer guidance to clinicians on applying motor imagery in neurorehabilitation and provide guidance to support this process.

METHOD

We used evidence from a variety of fields as well as clinical experience with motor imagery to develop guidance for employing motor imagery during neurorehabilitation.

RESULTS

Motor imagery is a relatively new intervention for neurorehabilitation supported by evidence from areas such as cognitive neuroscience and sports psychology. Motor imagery has become a very popular intervention modality for clinicians but there is insufficient information available on how to administer it in clinical practice and make deliberate decisions during its application.

CONCLUSIONS

We provide evidence-based guidance for employing motor imagery in neurorehabilitation and use the principles of motor learning as the framework for clinical application.

Could motor imagery be effective in upper limb rehabilitation of individuals with spinal cord injury? A case study

STUDY DESIGN

A case study.

OBJECTIVE

The aim was to investigate whether motor imagery (MI) could be successfully incorporated into conventional therapy among individuals with spinal cord injury (SCI) to improve upper limb (UL) function.

SETTING

The Physical Medicine and Rehabilitation Unit at the Henry Gabrielle Hospital in Lyon, France.

METHODS

The participant was an individual with a complete C6 SCI. MI content was focused on functional UL movements, to improve hand transport to reach out and grasp with tenodesis. The participant was tested before and after 15 MI training sessions (45 min each, three times a week during 5 consecutive weeks). MI ability and program compliance were used as indicators of feasibility. The Minnesota and Box and Blocks tests, as well as movement time and hand trajectory during targeted movements were the dependent variables, evaluating motor performance before and after MI training.

RESULTS

The participant's ability to generate MI was checked and compliance with the rehabilitation program was confirmed. The time needed to complete the Minnesota test decreased by 1 min 25 s. The Box and Blocks score was improved by three units after MI program. Decreased movement time and enhanced hand trajectory smoothness were still observed 3 months later, despite a slight decrease in performance.

CONCLUSIONS

This study supports the feasibility for introducing MI in conventional therapy. Further studies should confirm the potential role of MI in motor recovery with a larger sample.

Slowing of motor imagery after a right hemispheric stroke

The temporal congruence between real and imagined movements is not always preserved after stroke. We investigated the dependence of temporal incongruence on the side of the hemispheric lesion and its link with working memory deficits. Thirty-seven persons with a chronic stroke after a right or left hemispheric lesion (RHL : n = 19; LHL : n = 18) and 32 age-matched healthy persons (CTL) were administered a motor imagery questionnaire, mental chronometry and working memory tests. In contrast to persons in the CTL group and LHL subgroup, persons with a RHL had longer movement times during the imagination than the physical execution of stepping movements on both sides, indicating a reduced ability to predict movement duration (temporal incongruence). While motor imagery vividness was good in both subgroups, the RHL group had greater visuospatial working memory deficits. The bilateral slowing of stepping movements in the RHL group indicates that temporal congruence during motor imagery is impaired after a right hemispheric stroke and is also associated with greater visuospatial working memory deficits. Findings emphasize the need to use mental chronometry to control for movement representation during motor imagery training and may indicate that mental practice through motor imagery will have limitations in patients with a right hemispheric stroke.

Daytime naps improve motor imagery learning

Sleep is known to contribute to motor memory consolidation. Recent studies have provided evidence that a night of sleep plays a similar functional role following motor imagery (MI), while the simple passage of time does not result in performance gains. Here, we examined the benefits of a daytime nap on motor memory consolidation after MI practice. Participants were trained by MI on an explicitly known sequence of finger movements at 11:00. Half of the participants were then subjected (at 14:00) to either a short nap (10 min of stage 2 sleep) or a long nap (60-90 min, including slow wave sleep and rapid eye movement sleep). We also collected data from both quiet and active rest control groups. All participants remained in the lab until being retested at 16:00. The data revealed that a daytime nap after imagery practice improved motor performance and, therefore, facilitated motor memory consolidation, as compared with spending a similar time interval in the wake state. Interestingly, the results revealed that both short and long naps resulted in similar delayed performance gains. The data might also suggest that the presence of slow wave and rapid eye movement sleep does not provide additional benefits for the sleep-dependent motor skill consolidation following MI practice.

The relation between cognitive and motor dysfunction and motor imagery ability in patients with multiple sclerosis

Background:

Motor imagery (MI) was recently shown to be a promising tool in neurorehabilitation. The ability to perform MI, however, may be impaired in some patients with neurological dysfunction.

Objective:

The objective was to assess the relation between cognitive and motor dysfunction and MI ability in patients with multiple sclerosis (MS).

Methods:

Thirty patients with MS underwent cognitive and motor screening, and also performed a composite test battery to assess their MI ability. This test battery consisted of a questionnaire, a hand rotation task and a test based on mental chronometry. Patients’ MI ability was compared with the MI ability of age-matched healthy controls. Moreover, their MI scores were compared between body sides and were correlated with their scores on tests of motor and cognitive functioning.

Results:

The average accuracy and temporal organization of MI significantly differed between MS patients and controls. Patients’ MI accuracy significantly correlated with impairments in cognitive functioning, but was independent of motor functioning. MI duration, on the other hand, was independent of cognitive performance, but differed between the patients’ most and least affected side.

Conclusion:

These findings are of use when considering the application of MI practice in MS patients’ rehabilitation.

Training of executive functions in healthy elderly: Results of a pilot study

Executive functions (EF) refer to the cognitive skills necessary to formulate a goal, plan, execute plans effectively, and to perform self-monitoring and self-correction. Several aspects of EF change during the normal aging process.

The functional equivalence between movement imagery, observation, and execution influences imagery ability

Based on literature identifying movement imagery, observation, and execution to elicit similar areas of neural activity, research has demonstrated that movement imagery and observation successfully prime movement execution. To investigate whether movement and observation could prime ease of imaging from an external visual-imagery perspective, an internal visual-imagery perspective, and kinesthetic modality, 36 participants (M age = 20.58; SD = 3.11; 18 women and 18 men) completed an adapted version of the Movement Imagery Questionnaire-Revised under four modes of delivery (movement prime, external observation prime, internal observation prime, and image-only). The results revealed that ease of imaging was significantly greater during the movement and observation prime conditions compared to the image-only condition (p < .05). Specifically when priming external visual imagery and internal visual imagery, observation facilitated ease of imaging only when the perspective was congruent with the imagery perspective. The results support the use of movement and observation to facilitate ease of imaging, but highlight the importance of considering the visual perspective when using observation.

Measuring motor imagery using psychometric, behavioral, and psychophysiological tools

This review examines the measurement of motor imagery (MI) processes. First, self-report measures of MI are evaluated. Next, mental chronometry measures are considered. Then, we explain how physiological indices of the autonomic nervous system can measure MI. Finally, we show how these indices may be combined to produce a measure of MI quality called the Motor Imagery Index.

Rehabilitation--emerging technologies, innovative therapies, and future objectives

Stroke is the leading cause of long-term disability. The goal of stroke rehabilitation is to improve recovery in the years after a stroke and to decrease long-term disability. This article, titled "Rehabilitation--Emerging Technologies, Innovative Therapies, and Future Objectives" gives evidence-based information on the type of rehabilitation approaches that are effective to improve functional mobility and to address cognitive impairments. We review the importance of taking a translational approach to neurorehabilitation, considering the interaction of motor and cognitive systems, skilled learned purposeful limb movement, and spatial navigation ability. Known biologic mechanisms of neurorecovery are targeted in relation to technology implemented by members of the multidisciplinary team. Results from proof-of-concept, within subjects, and randomized controlled trials are presented, and the implications for optimal stroke rehabilitation strategies are discussed. Developing clinical practices are highlighted and future research directions are proposed with goals to provide insight on what the next steps are for this burgeoning discipline.

Mental practice for treating upper extremity deficits in individuals with hemiparesis after stroke

BACKGROUND

Activity limitations of the upper extremity are a common finding for individuals living with stroke. Mental practice (MP) is a training method that uses cognitive rehearsal of activities to improve performance of those activities.

OBJECTIVES

To determine if MP improves the outcome of upper extremity rehabilitation for individuals living with the effects of stroke.

SEARCH STRATEGY

We searched the Cochrane Stroke Group Trials Register (November 2010), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, November 2009), PubMed (1965 to November 2009), EMBASE (1980 to November 2009), CINAHL (1982 to November 2009), PsycINFO (1872 to November 2009), Scopus (1996 to November 2009), Web of Science (1955 to November 2009), the Physiotherapy Evidence Database (PEDro), CIRRIE, REHABDATA, ongoing trials registers, and also handsearched relevant journals and searched reference lists.

SELECTION CRITERIA

Randomised controlled trials involving adults with stroke who had deficits in upper extremity function.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion. We considered the primary outcome to be the ability of the arm to be used for appropriate tasks (i.e. arm function).

MAIN RESULTS

We included six studies involving 119 participants. We combined studies that evaluated MP in addition to another treatment versus the other treatment alone. Mental practice in combination with other treatment appears more effective in improving upper extremity function than the other treatment alone (Z = 3.48, P = 0.0005; standardised mean difference (SMD) 1.37; 95% confidence interval (CI) 0.60 to 2.15). We attempted subgroup analyses, based on time since stroke and dosage of MP; however, numbers in each group were small. We evaluated the quality of the evidence with the PEDro scale, ranging from 6 to 9 out of 10; we determined the GRADE score to be moderate.

AUTHORS' CONCLUSIONS

There is limited evidence to suggest that MP in combination with other rehabilitation treatment appears to be beneficial in improving upper extremity function after stroke, as compared with other rehabilitation treatment without MP. Evidence regarding improvement in motor recovery and quality of movement is less clear. There is no clear pattern regarding the ideal dosage of MP required to improve outcomes. Further studies are required to evaluate the effect of MP on time post stroke, volume of MP that is required to affect the outcomes and whether improvement is maintained long-term. Numerous large ongoing studies will soon improve the evidence base.

Recovery of motor imagery ability in stroke patients

Objective. To investigate whether motor imagery ability recovers in stroke patients and to see what the relationship is between different types of imagery and motor functioning after stroke. Methods. 12 unilateral stroke patients were measured at 3 and 6 weeks poststroke on 3 mental imagery tasks. Arm-hand function was evaluated using the Utrecht Arm-Hand task and the Brunnström Fugl-Meyer Scale. Age-matched healthy individuals (N = 10) were included as controls. Results. Implicit motor imagery ability and visual motor imagery ability improved significantly at 6 weeks compared to 3 weeks poststroke. Conclusion. Our study shows that motor imagery can recover in the first weeks after stroke. This indicates that a group of patients who might not be initially selected for mental practice can, still later in the rehabilitation process, participate in mental practice programs. Moreover, our study shows that mental imagery modalities can be differently affected in individual patients and over time.

Guided Motor Imagery in Healthy Adults and Stroke: Does Strategy Matter?

Background. Motor imagery (MI) enhances physical performance and skill acquisition in healthy and neurorehabilitation populations, yet little is known about the use of strategies to guide MI. Objectives. To examine the relative effectiveness of visual, auditory, and combined (visual + auditory) cueing of an imagined finger abduction task on corticomotor excitability. Methods. A total of 15 young (20-35 years) and 15 older people (over 55 years) and 10 people with chronic stroke, who could make voluntary movements of selected muscles, participated. Motor evoked potentials (MEPs, primary outcome) were measured following transcranial magnetic stimulation applied while participants imagined abducting their index finger under guidance of cueing strategies. Amplitudes of the MEPs from the first dorsal interosseous (FDI), abductor pollicis brevis (APB), and abductor digiti minimi (ADM) muscles were compared with rest, contrasted with MEPs elicited during active task performance, and expressed relative to rest to reflect facilitation. Results. Cued MI enhanced MEPs in all groups, preferentially to the target FDI muscle. In stroke, APB was also facilitated. ADM was least affected by cueing. Analyses of simple effects of condition on FDI MEPs in each group revealed that visual cueing was most effective in young people, whereas auditory cueing was most effective in healthy older people and when directed at the nonparetic side in stroke ( P < .04). On the paretic side, strategies were equally effective. In all cases, MEPs were largest during physical performance. Conclusions. Cued MI augments corticomotor excitability associated with healthy and paretic muscles related to the imagined task. Age should be considered when selecting a cueing strategy for maximum effectiveness.

Mental practice for relearning locomotor skills

Over the past 2 decades, much work has been carried out on the use of mental practice through motor imagery for optimizing the retraining of motor function in people with physical disabilities. Although much of the clinical work with mental practice has focused on the retraining of upper-extremity tasks, this article reviews the evidence supporting the potential of motor imagery for retraining gait and tasks involving coordinated lower-limb and body movements. First, motor imagery and mental practice are defined, and evidence from physiological and behavioral studies in healthy individuals supporting the capacity to imagine walking activities through motor imagery is examined. Then the effects of stroke, spinal cord injury, lower-limb amputation, and immobilization on motor imagery ability are discussed. Evidence of brain reorganization in healthy individuals following motor imagery training of dancing and of a foot movement sequence is reviewed, and the effects of mental practice on gait and other tasks involving coordinated lower-limb and body movements in people with stroke and in people with Parkinson disease are examined. Lastly, questions pertaining to clinical assessment of motor imagery ability and training strategies are discussed.

Comparison of embedded and added motor imagery training in patients after stroke: study protocol of a randomised controlled pilot trial using a mixed methods approach

BACKGROUND

Two different approaches have been adopted when applying motor imagery (MI) to stroke patients. MI can be conducted either added to conventional physiotherapy or integrated within therapy sessions. The proposed study aims to compare the efficacy of embedded MI to an added MI intervention. Evidence from pilot studies reported in the literature suggests that both approaches can improve performance of a complex motor skill involving whole body movements, however, it remains to be demonstrated, which is the more effective one.

METHODS/DESIGN

A single blinded, randomised controlled trial (RCT) with a pre-post intervention design will be carried out. The study design includes two experimental groups and a control group (CG). Both experimental groups (EG1, EG2) will receive physical practice of a clinical relevant motor task ('Going down, laying on the floor, and getting up again') over a two week intervention period: EG1 with embedded MI training, EG2 with MI training added after physiotherapy. The CG will receive standard physiotherapy intervention and an additional control intervention not related to MI. The primary study outcome is the time difference to perform the task from pre to post-intervention. Secondary outcomes include level of help needed, stages of motor task completion, degree of motor impairment, balance ability, fear of falling measure, motivation score, and motor imagery ability score. Four data collection points are proposed: twice during baseline phase, once following the intervention period, and once after a two week follow up. A nested qualitative part should add an important insight into patients' experience and attitudes towards MI. Semi-structured interviews of six to ten patients, who participate in the RCT, will be conducted to investigate patients' previous experience with MI and their expectations towards the MI intervention in the study. Patients will be interviewed prior and after the intervention period.

DISCUSSION

Results will determine whether embedded MI is superior to added MI. Findings of the semi-structured interviews will help to integrate patient's expectations of MI interventions in the design of research studies to improve practical applicability using MI as an adjunct therapy technique.

Aging affects the mental rotation of left and right hands

BACKGROUND

Normal aging significantly influences motor and cognitive performance. Little is known about age-related changes in action simulation. Here, we investigated the influence of aging on implicit motor imagery.

METHODOLOGY/PRINCIPAL FINDINGS

Twenty young (mean age: 23.9+/-2.8 years) and nineteen elderly (mean age: 78.3+/-4.5 years) subjects, all right-handed, were required to determine the laterality of hands presented in various positions. To do so, they mentally rotated their hands to match them with the hand-stimuli. We showed that: (1) elderly subjects were affected in their ability to implicitly simulate movements of the upper limbs, especially those requiring the largest amplitude of displacement and/or with strong biomechanical constraints; (2) this decline was greater for movements of the non-dominant arm than of the dominant arm.

CONCLUSIONS/SIGNIFICANCE

These results extend recent findings showing age-related alterations of the explicit side of motor imagery. They suggest that a general decline in action simulation occurs with normal aging, in particular for the non-dominant side of the body.

The effect of two physiotherapy approaches on physical and cognitive functions and independent coping at home in stroke rehabilitation. A preliminary follow-up study

PURPOSE

Activating physiotherapy was used to support the principle of post stroke functional recovery as a learning process which requires both cognitive and physical actions. The purpose of the present preliminary study was to examine the influence of activating physiotherapy on stroke patients' cognitive and physical functions and independent living at home compared with traditional treatment over a 12-month follow-up.

METHODS

The 40 patients who received activating physiotherapy were compared with 40 patients receiving traditional therapy. Patients' physical functional capacity was measured one week and 12 months post stroke with the Barthel Index (BI), 10-m gait speed, the Postural Control and Balance for Stroke (PCBS) test, walking distances and patients' abilities to cope without outside help. Cognitive capacity was measured with specific neuropsychological tests: language, visuospatial functions, visual inattention and memory.

RESULTS

Physical functional capacity improved significantly (p = 0.001) in both groups at the 12-month follow-up, but no significant differences were found between groups. However, the patients in the activating therapy group coped better without outside help (p = 0.042) and covered longer distances outdoors (p = 0.012). At follow-up all the measured cognitive functions had improved significantly in the activating therapy group and the change in memory in the same group differed significantly from that in the traditional therapy group (p < 0.001), where no significant improvement was observed.

CONCLUSIONS

Activating therapy advanced stroke patients' cognitive and physical functional recovery and supported their return to independent life at home more than did traditional physiotherapy. In this respect activating therapy seems to have a beneficial influence on long-term stroke rehabilitation.

Computerized working memory training after stroke–A pilot study

AIM

To examine the effects of working memory (WM) training in adult patients with stroke.

METHODS

A randomized pilot study with a treatment group and a passive control group; 18 participants (12 males) in a vocational age group (mean age 54 years) were randomized to either the treatment or the control condition. The intervention consisted of computerized training on various WM tasks for five weeks. A neuropsychological test battery and self-rating on cognitive functioning in daily life (the CFQ) were administered both before and after the treatment.

RESULTS

Statistically significant training effects were found on the non-trained tests for WM and attention, i.e., tests that measure related cognitive functions but are not identical to tasks in the training programme (Span board p < 0.05; PASAT p < 0.001; Ruff 2&7 p < 0.005). There was a significant decrease in symptoms of cognitive problems as measured by the CFQ (p < 0.005).

CONCLUSION

More than one year after a stroke, systematic WM training can significantly improve WM and attention.

Using mental practice in stroke rehabilitation: a framework

Introduction: Motor imagery and mental practice are getting increased attention in neurological rehabilitation. Several different mental practice intervention protocols have been used in studies on its effect on recovery in stroke rehabilitation. The content of the intervention protocols itself is rarely discussed or questioned.

Objective: To give a practical framework of how mental practice could be integrated into therapy, drawing on available evidence and theory. The aim of the treatment programme described is to enhance both the patient's physical performance and their empowerment and self-determination.

The framework: Based on evidence from sports rehabilitation and our own experiences the framework will eventually be evaluated in a randomized controlled trial. Five steps are described to teach and upgrade the patient's imagery technique: (1) assess mental capacity to learn imagery technique; (2) establish the nature of mental practice; (3) teach imagery technique; (4) embed and monitor imagery technique; (5) develop self-generated treatments. The description is not, however, a recipe that should be followed precisely. It leaves enough room to tailor the mental practice intervention to the specific individual possibilities, skills and needs of the patient in accordance with evidence-based practice.

Discussion: Different aspects of the described protocol are discussed and compared with experiences from sports and evidence available in rehabilitation.

Clinical Assessment of Motor Imagery After Stroke

Objective . The aim of this study was to investigate: (1) the effects of a stroke on motor imagery vividness as measured by the Kinesthetic and Visual Imagery Questionnaire (KVIQ-20); (2) the influence of the lesion side; and (3) the symmetry of motor imagery. Methods. Thirty-two persons who had sustained a stroke, in the right (n = 19) or left (n = 13) cerebral hemisphere, and 32 age-matched healthy persons participated. The KVIQ-20 assesses on a 5-point ordinal scale the clarity of the image (visual scale) and the intensity of the sensations (kinesthetic scale) that the subjects are able to imagine from the first-person perspective. Results. In both groups, the visual scores were higher ( P = .0001) than the kinesthetic scores and there was no group difference. Likewise, visual scores remained higher than kinesthetic scores irrespective of the lesion side. The visual scores poststroke were higher ( P = .001) when imagining upper limb movements on the unaffected side than those on the affected side. When focusing on the lower limb only, however, the kinesthetic scores were higher ( P = .001) when imagining movements of the unaffected compared to those on the affected side. Conclusions. The vividness of motor imagery poststroke remains similar to that of age-matched healthy persons and is not affected by the side of the lesion. However, after stroke motor imagery is not symmetrical and motor imagery vividness is better when imagining movements on the unaffected than on the affected side, indicating an overestimation possibly related to a hemispheric imbalance or a recalibration of motor imagery perception.

Effects of mental practice embedded in daily therapy compared to therapy as usual in adult stroke patients in Dutch nursing homes: design of a randomised controlled trial

Background

Mental practice as an additional cognitive therapy is getting increased attention in stroke rehabilitation. A systematic review shows some evidence that several techniques in which movements are rehearsed mentally might be effective but not enough to be certain. This trial investigates whether mental practice can contribute to a quicker and/or better recovery of stroke in two Dutch nursing homes. The objective is to investigate the therapeutic potential of mental practice embedded in daily therapy to improve individually chosen daily activities of adult stroke patients compared to therapy as usual. In addition, we will investigate prognostic variables and feasibility (process evaluation).

Methods

A randomised, controlled, observer masked prospective trial will be conducted with adult stroke patients in the (sub)acute phase of stroke recovery. Over a six weeks intervention period the control group will receive multi professional therapy as usual. Patients in the experimental group will be instructed how to perform mental practice, and will receive care as usual in which mental practice is embedded in physical, occupation and speech therapy sessions. Outcome will be assessed at six weeks and six months. The primary outcome measure is the patient-perceived effect on performance of daily activities as assessed by an 11-point Likert Scale. Secondary outcomes are: Motricity Index, Nine Hole Peg Test, Barthel Index, Timed up and Go, 10 metres walking test, Rivermead Mobility Index. A sample size of the patients group and all therapists will be interviewed on their opinion of the experimental program to assess feasibility. All patients are asked to keep a log to determine unguided training intensity.

Discussion

Advantages and disadvantages of several aspects of the chosen design are discussed.

Trial registration

ISRCTN27582267

Motor imagery in physical therapist practice

Motor imagery is the mental representation of movement without any body movement. Abundant evidence on the positive effects of motor imagery practice on motor performance and learning in athletes, people who are healthy, and people with neurological conditions (eg, stroke, spinal cord injury, Parkinson disease) has been published. The purpose of this update is to synthesize the relevant literature about motor imagery in order to facilitate its integration into physical therapist practice. This update also will discuss visual and kinesthetic motor imagery, factors that modify motor imagery practice, the design of motor imagery protocols, and potential applications of motor imagery.

Movement-specific enhancement of corticospinal excitability at subthreshold levels during motor imagery

This study examined modulation of corticospinal excitability during both actual and imagined movements. Seven young healthy subjects performed actual (3-50% maximal voluntary contractions) and imagined index finger force production, and rest. Individual responses to focal transcranial magnetic stimulation (TMS) in four fingers (index, middle, ring, and little) were recorded for all three tested conditions. The force increments at the threshold of activation were predicted from regression analysis, representing the TMS-induced response at the threshold activation of the corticospinal pathways. The measured increment in the index finger during motor imagery was larger than that at rest, but smaller than the predicted increment at the threshold of activation. On the other hand, the measured increment in the uninstructed (middle, ring, and little), slave fingers during motor imagery was larger than that at rest, but not different from the predicted increment at the threshold of activation. These contrasting results suggest that the degree of imagery-induced enhancement in corticospinal excitability was significantly less than what could be predicted for threshold levels from regression analysis, but only for the index finger, and not the adjacent slave fingers. It is concluded that corticospinal excitability for the explicitly instructed index finger is specifically enhanced at subthreshold levels during motor imagery.

Using treatment theories to refine the designs of brain injury rehabilitation treatment effectiveness studies

Many rehabilitation treatments are difficult to define, resulting in a lack of clarity about their essential "active ingredients." Treatment theories can narrow the scope of possible active ingredients, by clearly specifying how the treatment is believed to act. Efficacy studies of theory-defined treatments assess their clinical value, but also advance the science underlying the theory. In addition, treatment theories shape inclusion and exclusion criteria by suggesting what types of patients may benefit, and shape outcome measures by suggesting where the treatment impact should be seen. Finally, treatment theories can assist an investigator in the selection of an optimal study design.

Motor Imagery

Background and Purpose— Understanding brain plasticity after stroke is important in developing rehabilitation strategies. Active movement therapies show considerable promise but depend on motor performance, excluding many otherwise eligible patients. Motor imagery is widely used in sport to improve performance, which raises the possibility of applying it both as a rehabilitation method and to access the motor network independently of recovery. Specifically, whether the primary motor cortex (M1), considered a prime target of poststroke rehabilitation, is involved in motor imagery is unresolved.

Summary of Review— We review methodological considerations when applying motor imagery to healthy subjects and in patients with stroke, which may disrupt the motor imagery network. We then review firstly the motor imagery training literature focusing on upper-limb recovery, and secondly the functional imaging literature in healthy subjects and in patients with stroke.

Conclusions— The review highlights the difficulty in addressing cognitive screening and compliance in motor imagery studies, particularly with regards to patients with stroke. Despite this, the literature suggests the encouraging effect of motor imagery training on motor recovery after stroke. Based on the available literature in healthy volunteers, robust activation of the nonprimary motor structures, but only weak and inconsistent activation of M1, occurs during motor imagery. In patients with stroke, the cortical activation patterns are essentially unexplored as is the underlying mechanism of motor imagery training. Provided appropriate methodology is implemented, motor imagery may provide a valuable tool to access the motor network and improve outcome after stroke.

Working memory and acquisition of implicit knowledge by imagery training, without actual task performance

This study investigated acquisition of a mirror-reading skill via imagery training, without the actual performance of a mirror-reading task. In experiment I, healthy volunteers simulated writing on an imaginary, transparent screen placed at eye level, which could be read by an experimenter facing the subject. Performance of this irrelevant motor task required the subject to imagine the letters inverted, as if seen in a mirror from their own point of view (imagery training). A second group performed the same imagery training interspersed with a complex, secondary spelling and counting task. A third, control, group simply wrote the words as they would normally appear from their own point of view. After training with 300 words, all subjects were tested in a mirror-reading task using 60 non-words, constructed according to acceptable letter combinations of the Portuguese language. Compared with control subjects, those exposed to imagery training, including those who switched between imagery and the complex task, exhibited shorter reading times in the mirror-reading task. Experiment II employed a 2 x 3 design, including two training conditions (imagery and actual mirror-reading) and three competing task conditions (a spelling and counting switching task, a visual working memory concurrent task, and no concurrent task). Training sessions were interspersed with mirror-reading testing sessions for non-words, allowing evaluation of the mirror-reading acquisition process during training. The subjects exposed to imagery training acquired the mirror-reading skill as quickly as those exposed to the actual mirror-reading task. Further, performance of concurrent tasks together with actual mirror-reading training severely disrupted mirror-reading skill acquisition; this interference effect was not seen in subjects exposed to imagery training and performance of the switching and the concurrent tasks. These results unequivocally show that acquisition of implicit skills by top-down imagery training is at least as efficient as bottom-up acquisition.

Kinesthetic, but not visual, motor imagery modulates corticomotor excitability

The hypothesis that motor imagery and actual movement involve overlapping neural structures in the central nervous system is supported by multiple lines of evidence. The aim of this study was to examine the modulation of corticomotor excitability during two types of strategies for motor imagery: Kinesthetic Motor Imagery (KMI) and Visual Motor Imagery (VMI) in a phasic thumb movement task. Transcranial magnetic stimulation (TMS) was applied over the contralateral motor cortex (M1) to elicit motor evoked potentials (MEPs) in the dominant abductor pollicis brevis (APB) and abductor digiti minimi (ADM). In a separate experiment, transcutaneous electrical stimuli were delivered to the median nerve at the dominant wrist, to elicit F-waves from APB. Imagined task performance was paced with a 1 Hz auditory metronome, and stimuli were delivered either 50 ms before (ON phase), or 450 ms after (OFF phase), the metronome beeps. Recordings were also made during two control conditions: Rest, and a Visual Static Imagery (VSI) condition. Significant MEP amplitude facilitation occurred only in APB, and only during the ON phase of KMI. F-wave persistence and amplitude were unaffected by imagery. These results demonstrate that kinesthetic, but not visual, motor imagery modulates corticomotor excitability, primarily at the supraspinal level. These findings have implications for the definition of motor imagery, and for its therapeutic applications.

Strategies for stroke rehabilitation

Rehabilitation after hemiplegic stroke has typically relied on the training of patients in compensatory strategies. The translation of neuroscientific research into care has led to new approaches and renewed promise for better outcomes. Improved motor control can progress with task-specific training incorporating increased use of proximal and distal movements during intensive practice of real-world activities. Functional gains are incorrectly said to plateau by 3-6 months. Many patients retain latent sensorimotor function that can be realised any time after stroke with a pulse of goal-directed therapy. The amount of practice probably best determines gains for a given level of residual movement ability. Clinicians should encourage patients to build greater strength, speed, endurance, and precision of multijoint movements on tasks that increase independence and enrich daily activity. Imaging tools may help clinicians determine the capacity of residual networks to respond to a therapeutic approach and help establish optimal dose-response curves for training. Promising adjunct approaches include practice with robotic devices or in a virtual environment, electrical stimulation to increase cortical excitability during training, and drugs to optimise molecular mechanisms for learning. Biological strategies for neural repair may augment rehabilitation in the next decade.

Bilateral slowing of mentally simulated actions after stroke

The ability to mentally simulate motor actions was studied in 25 patients with stroke. The duration of imagined and executed movements of the arm and leg was compared. Both executed and imagined movements took longer with the affected limbs than with the unaffected limbs. For both tasks, the duration of movements with the unaffected limbs was longer in the imagined than in the executed conditions, indicating a lack of temporal congruence on that side. Because the temporal uncoupling was found in the limbs contralateral to the intact hemisphere, we propose that this reflects a general slowing in motor imagery that is an indirect consequence of the lesion, rather than a deficit in movement representation within the unaffected hemisphere per se.

Brain plasticity in health and disease

Research during the last decades has greatly increased our understanding of brain plasticity, i.e. how neuronal circuits can be modified by experience, learning and in response to brain lesions. Currently available neuroimaging techniques that make it possible to study the function of the human brain in vivo have had an important impact. Cross-modal plasticity during development is demonstrated by cortical reorganization in blind or deaf children. Early musical training has lasting effects in shaping the brain. Albeit the plasticity is largest during childhood, the adult brain retains a capacity for functional and structural reorganization that earlier has been underestimated. Recent research on Huntington's disease has revealed the possibility of environmental interaction even with dominant genes. Scientifically based training methods are now being applied in rehabilitation of patients after stroke and trauma, and in the sensory retraining techniques currently applied in the treatment of focal hand dystonia as well as in sensory re-education after nerve repair in hand surgery. There is evidence that frequent participation in challenging and stimulating activities is associated with reduced cognitive decline during aging. The current concept of brain plasticity has wide implication for areas outside neuroscience and for all human life.