Potential role of mental practice using motor imagery in neurologic rehabilitation

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.

Limb (hand vs. foot) and response conflict have similar effects on event-related potentials (ERPs) recorded during motor imagery and overt execution

Although there is substantial evidence that motor execution (M-Ex) and motor imagery (M-Im) share a common neural substrate, the role of the primary motor cortex (M1) during imagery is still a matter of debate. The present ERP study tries to clarify the functional similarity between the two processes in respect of (i) the engagement of the corresponding somatotopic M1 areas during execution and imagery of hand vs. foot movements; and (ii) the effect of conflicting information on response preparation. To this end, we recorded ERPs from 28 electrode sites in 19 participants while they performed a conflict task with congruent (target and flanker arrowheads pointing in the same direction) and incongruent (target pointing in the opposite direction to the flanker arrowheads) trials. We obtained the lateralized readiness potential (LRP), a component generated in M1, while subjects physically executed or mentally simulated the task. As expected by the somatotopic organization of M1, the LRP was of opposite polarity when foot, rather than hand, movements were prepared. The inversion of polarity also occurred during M-Im, a result that strongly argues in favour of the participation of M1 in motor imagery. In incongruent trials, longer LRP latencies, a premature preparation of the incorrect response (positive deflection in LRP waveform) and a fronto-central N2 component associated with response conflict appeared during both M-Ex and M-Im. Altogether, the results support the functional equivalence of the two processes and give support to the clinical use of M-Im for the improvement and recovery of motor functions.

Motor imagery

We describe general concepts about motor imagery and differences to motor execution. The problem of controlling what the subject actually does during imagery is emphasized. A major part of the chapter is dealing with mental training by imagery and the usage of motor imagination in athletes, musicians and during rehabilitation. Data of altered representations of the body after loss of afferent information and motor representation due to limb amputation or complete spinal cord injury are demonstrated and discussed. Finally we provide an outlook on additional work about motor imagery important for further understanding of the topic.

The Effects of Mental Practice in Stroke Rehabilitation: A Systematic Review

OBJECTIVE

To assess the effects of a mental practice intervention on recovery in stroke patients.

DATA SOURCES

A systematic literature search of the Cochrane Database of Systematic Reviews, PubMed/Medline, PsycINFO, Pedro, Rehadat, and RehabTrials was performed by 2 researchers independently. Eligible studies published through August 2005 were selected.

STUDY SELECTION

Four randomized controlled trials (RCTs), 1 controlled clinical trial (CCT), 2 patient series, and 3 case reports that investigated the effects of a mental practice intervention on recovery of stroke patients were included.

DATA EXTRACTION

The selected RCTs and CCT were assessed on a methodologic quality rating scale. Important characteristics and outcomes were extracted and summarized. Results and characteristics from the patient series and case reports were only provided if they added information.

DATA SYNTHESIS

Included studies differed clearly from one another with regard to patient characteristics, intervention protocol, and outcome measures. Four different mental practice strategies were used. Most tasks involved mentally rehearsing movements of the arm. Intervention periods varied from 2 to 6 weeks, frequencies ranged from multiple sessions per day to 3 times a week. Studies were limited in size. Power could not be increased by pooling or meta-analysis because studies were not comparable. Three of the 4 RCTs were of reasonable methodologic quality. There was some evidence that mental practice as an additional therapy intervention had positive effects on recovery of arm function after stroke. Two mental practice techniques appeared to be effective-tape instruction and self-regulation. Results from the single case studies indicate that mental practice is also promising for improvement of leg function.

CONCLUSIONS

No definite conclusions could be drawn except that further research, using clear definitions of the content of mental practice and standardized measurement of outcome, are needed.

Brain activation during execution and motor imagery of novel and skilled sequential hand movements

This experiment used functional magnetic resonance imaging (fMRI) to compare functional neuroanatomy associated with executed and imagined hand movements in novel and skilled learning phases. We hypothesized that 1 week of intensive physical practice would strengthen the motor representation of a hand motor sequence and increase the similarity of functional neuroanatomy associated with executed and imagined hand movements. During fMRI scanning, a right-hand self-paced button press sequence was executed and imagined before (NOVEL) and after (SKILLED) 1 week of intensive physical practice (n = 54; right-hand dominant). The mean execution rate was significantly faster in the SKILLED (3.8 Hz) than the NOVEL condition (2.5 Hz) (P < 0.001), but there was no difference in execution errors. Activation foci associated with execution and imagery was congruent in both the NOVEL and SKILLED conditions, though activation features were more similar in the SKILLED versus NOVEL phase. In the NOVEL phase, activations were more extensive during execution than imagery in primary and secondary cortical motor volumes and the cerebellum, while during imagery activations were greater in the striatum. In the SKILLED phase, activation features within these same volumes became increasingly similar for execution and imagery, though imagery more heavily activated premotor areas, inferior parietal lobe, and medial temporal lobe, while execution more heavily activated the precentral/postcentral gyri, striatum, and cerebellum. This experiment demonstrated congruent activation of the cortical and subcortical motor system during both novel and skilled learning phases, supporting the effectiveness of motor imagery-based mental practice techniques for both the acquisition of new skills and the rehearsal of skilled movements.

Empathy examined through the neural mechanisms involved in imagining how I feel versus how you feel pain

Perspective-taking is a stepping stone to human empathy. When empathizing with another individual, one can imagine how the other perceives the situation and feels as a result. To what extent does imagining the other differs from imagining oneself in similar painful situations? In this functional magnetic resonance imaging experiment, participants were shown pictures of people with their hands or feet in painful or non-painful situations and instructed to imagine and rate the level of pain perceived from different perspectives. Both the Self's and the Other's perspectives were associated with activation in the neural network involved in pain processing, including the parietal operculum, anterior cingulate cortex (ACC; BA32) and anterior insula. However, the Self-perspective yielded higher pain ratings and involved the pain matrix more extensively in the secondary somatosensory cortex, the ACC (BA 24a'/24b'), and the insula proper. Adopting the perspective of the Other was associated with specific increase in the posterior cingulate/precuneus and the right temporo-parietal junction. These results show the similarities between Self- and Other-pain representation, but most interestingly they also highlight some distinctiveness between these two representations, which is a crucial aspect of human empathy. It may be what allows us to distinguish empathic responses to others versus our own personal distress. These findings are consistent with the view that empathy does not involve a complete Self-Other merging.

Évolution des concepts en rééducation du patient hémiplégique

INTRODUCTION

The author attempts to show the evolution of the ideas guiding the rehabilitation treatment of motricity disorders after a vascular or traumatic brain lesion.

METHOD

Expert opinion based on an uncomprehensive review of the literature, from the databases Reedoc and Medline and from the Institut Lionnois library in Nancy and the Charcot library in Paris.

RESULTS AND DISCUSSION

Many theories and techniques have been proposed. The modern history of this rehabilitation treatment has been marked by a period that stressed control of the abnormal motricity characterizing central motor disorders, sometimes too exclusively. The development of evidence-based medicine in the 1980s undermined certain dogmas. At the same time, the advent of cerebral imaging technology confirmed clinical observations and hypotheses concerning cerebral plasticity. Today, the rehabilitation treatment of these motor disorders uses notions of learning; the diversity and complementarity of the exercises, which must be task-oriented; relative earliness and intensity of therapy; close interactions between sensitivity and motricity; and different concepts as mental imagery, the perception of verticality, or muscle strengthening.

CONCLUSION

To its well-known preventive and palliative roles, rehabilitation treatment has now added a curative role. All the concepts applied today are not new, but the spirit of their application is new. Because we are sure that neurological recovery can be improved, no idea can be rejected at the outset; its effect must be demonstrated. Among the numerous ideas presently proposed, future studies will define the best ones, for the most suitable patient, at the best time.

Imagery-induced cortical excitability changes in stroke: a transcranial magnetic stimulation study

Focal transcranial magnetic stimulation (TMS) was employed in a population of hemiparetic stroke patients in a post-acute stage to map out the abductor digiti minimi (ADM) muscle cortical representation of the affected (AH) and unaffected (UH) hemisphere at rest, during motor imagery and during voluntary contraction. Imagery induced an enhancement of the ADM map area and volume in both hemispheres in a way which partly corrected the abnormal asymmetry between AH and UH motor output seen in rest condition. The voluntary contraction was the task provoking maximal facilitation in the UH, whereas a similar degree of facilitation was obtained during voluntary contraction and motor imagery in the AH. We argued that motor imagery could induce a pronounced motor output enhancement in the hemisphere affected by stroke. Further, we demonstrated that imagery-induced excitability changes were specific for the muscle 'prime mover' for the imagined movement, while no differences were observed with respect to the stroke lesion locations. Present findings demonstrated that motor imagery significantly enhanced the cortical excitability of the hemisphere affected by stroke in a post-acute stage. Further studies are needed to correlate these cortical excitability changes with short-term plasticity therefore prompting motor imagery as a 'cortical reservoir' in post-stroke motor rehabilitation.

Physical practice induces excitability changes in human hand motor area during motor imagery

The present study was undertaken to investigate the effects of physical practice on excitability changes in human primary motor cortex (M1) during motor imagery (MI). Using different intensities of transcranial magnetic stimulation (TMS), we examined changes in the motor evoked potential (MEP) of the first dorsal interosseous (FDI) muscle with and without MI, and before and after physical practice. On comparing results for MEPs recorded before and after physical practice, the difference between the MEP amplitudes observed at rest and during MI only increased at higher TMS intensities. This finding indicates a physical practice-dependent increase of the higher threshold recruitment of corticospinal tract neurons (CTNs), consistent with synchronization for efficient movement, and provides evidence that neural mechanisms of MI depend not only on the type of movement but also on the extent of the motor adaptation (the physical practice). These present findings also show the benefit of MI and highlight beneficial neural mechanisms related to the activation of M1 during MI. In other words, MI may reflect functional changes of M1 that are similar to the changes observed after physical practice.

Motor cortex excitability following repetitive electrical stimulation of the common peroneal nerve depends on the voluntary drive

Previously, long-term changes in the motor cortex have been reported after repetitive electrical nerve stimulation (rES) as well as after motor exercise. The purpose of this study was to investigate whether the effects of voluntary motor cortical drive and of rES on the motor cortical output in healthy subjects interact with each other. A 30-min exercise session was performed during the following conditions: rES of the right common peroneal nerve (CPN) during rES at rest (A); voluntary exercise of the right ankle dorsiflexors alone (B); rES combined with voluntary dorsiflexion exercise (C); voluntary exercise of ankle plantar flexors alone (D); and plantar flexion exercise combined with rES (E). Motor evoked potentials (MEPs) were obtained before and after the exercise with a stimulation intensity of 125% of the threshold of the relaxed right tibialis anterior (TA). rES was ON for 1 s and OFF for 2 s in a cycle, and consisted of trains of five pulses, duration 1 ms and frequency 30 Hz, as applied in functional electrical stimulation (FES). MEPs of the TA muscle elicited after the training were increased in A by 38%, in B by 35%, and in C by 66%. In D and E, the MEPs of TA were decreased by 29% and 35%, respectively. The effect was maintained for at least 30 min after the nerve stimulation was completed. Consistent with previous studies (Khaslavskaia et al. (2002) Exp Brain Res 145:309-315), MEPs after the CPN rES are shown to be partly due to increased TA cortical excitability. These results suggest that the effect of FES on motor cortical excitability depends on the concurrent motor cortical drive present at the time of FES, and the combination of these factors modulates neural excitability and probably reorganization. The decrease in motor cortical excitability after plantar flexor exercise probably means that voluntary effort antagonistic to the electrical exercise is stronger and cancels out the effects of rES. Improving FES effects through an agonist voluntary drive implies an enhancement of sensorimotor reorganization through the addition of a voluntary component to a trained movement. Possible mechanisms and implications of these results on the rehabilitation of patients with paralysis and spasticity are discussed.

How do we perceive the pain of others? A window into the neural processes involved in empathy

To what extent do we share feelings with others? Neuroimaging investigations of the neural mechanisms involved in the perception of pain in others may cast light on one basic component of human empathy, the interpersonal sharing of affect. In this fMRI study, participants were shown a series of still photographs of hands and feet in situations that are likely to cause pain, and a matched set of control photographs without any painful events. They were asked to assess on-line the level of pain experienced by the person in the photographs. The results demonstrated that perceiving and assessing painful situations in others was associated with significant bilateral changes in activity in several regions notably, the anterior cingulate, the anterior insula, the cerebellum, and to a lesser extent the thalamus. These regions are known to play a significant role in pain processing. Finally, the activity in the anterior cingulate was strongly correlated with the participants' ratings of the others' pain, suggesting that the activity of this brain region is modulated according to subjects' reactivity to the pain of others. Our findings suggest that there is a partial cerebral commonality between perceiving pain in another individual and experiencing it oneself. This study adds to our understanding of the neurological mechanisms implicated in intersubjectivity and human empathy.

Motor Imagery for Gait Rehabilitation in Post-Stroke Hemiparesis

Background and Purpose. Reports have described the contribution of motor imagery (MI) practice for improving upper-extremity functions in patients with hemiparesis following stroke. The purpose of this case report is to describe the use of MI practice to attempt to improve walking in an individual with hemiparesis. Case Description. A 69-year-old man with left hemiparesis received MI gait practice for 6 weeks. Intervention focused on task-oriented gait and on impairments of the affected lower limb. Preintervention, midterm, postintervention, and follow-up measurements of temporal-distance stride parameters and sagittal kinematics of the knee joint were taken. Main Outcomes. At 6 weeks postintervention, the patient had a 23% increase in gait speed and a 13% reduction in double-support time. An increase in range of motion of the knees also was observed. No changes in gait symmetry were noted. Discussion. The outcomes suggest that MI may be useful for the enhancement of walking ability in patients following stroke. Because improvement was mainly in temporal-distance gait variables and knee movement, imagery practice probably should focus on its specific impairments during gait in order to affect the performance of the paretic lower extremity.

Training with Computer-Supported Motor Imagery in Post-Stroke Rehabilitation

Converging lines of evidence suggest that motor imagery (the mental simulation of a motor act within working memory) is associated with subliminal activation of the motor system. This observation has led to the hypothesis that cortical activation during motor imagery may affect the acquisition of specific motor skills and help the recovery of motor function. In this paper, we describe a clinical protocol in which we use interactive tools to stimulate motor imagery in hemiplegic stroke patients, thereby helping them to recover lost motor function. The protocol consists of an inpatient and an outpatient phase, combining physical and mental practice. In the inpatient phase, patients are trained in a laboratory setting, using a custom-made interactive workbench (VR Mirror). After discharge, patients use a portable device to guide mental and physical practice in a home setting. The proposed strategy is based on the hypotheses that: (a) combined physical and mental practice can make a cost-effective contribution to the rehabilitation of stroke patients, (b) effective mental practice is not possible without some form of support, from a therapist (as in our inpatient phase) or from technology (as in the outpatient phase), (c) the inclusion of an outpatient phase will allow the patient to practice more often than would otherwise be possible, therefore increasing the speed and/or effectiveness of learning, and (d) the use of interactive technology will reduce the patient's need for skilled support, therefore improving the cost-effectiveness of training.

Long lasting effects of transcranial direct current stimulation on motor imagery

Transcranial magnetic stimulation (TMS) was employed to probe the modulatory effects of transcranial direct current stimulation of motor cortex on motor evoked responses (MEPs) produced during motor imagery. MEP amplitudes at rest and during motor imagery were assessed before and for a period of 60 min after transcranial direct current stimulation (tDCS) applied over the primary motor cortex at 1 mA for 5 min. Cathodal stimulation induced a decrease of about 30% of MEP amplitude at rest and a 50% reduction of MEP size during imagery. Ten minutes after tDCS, MEPs at rest returned to baseline values while MEPs during motor imagery were suppressed for up to 30 min. No changes in MEP amplitude during imagery were found after anodal stimulation. tDCS could represent a powerful tool to modulate the excitability of motor areas involved in mental practice and motor imagery.

Modulation of corticospinal excitability and intracortical inhibition during motor imagery is task-dependent

Previous studies have clearly shown that motor imagery modulates corticospinal excitability. However, there is no clear evidence for the modulation of intracortical inhibition (ICI) during imagined task performance. The aim of this study was to use transcranial magnetic stimulation (TMS) to assess changes in corticospinal excitability and ICI during the imagined performance of two types of task. In Experiment 1, eight subjects performed phasic depression of a computer mouse button using the dominant index finger in time with a 1 Hz auditory metronome. Single and paired pulse magnetic stimuli were delivered at rest, and during the 'on' and 'off' phases of actual and imagined task performance. Motor evoked potentials (MEPs) were recorded from FDI and APB. In Experiment 2, eight subjects performed phasic isometric abduction of the dominant thumb in time with a 1 Hz auditory metronome. As before, single and paired pulse magnetic stimuli were delivered at rest, and during the 'on' and 'off' phases of actual and imagined task performance. In both experiments, the conditioning stimulus intensity was set to produce 50% inhibition at rest, to enable both increases and decreases in ICI during task performance to be detected. No significant temporal or spatial modulation of MEP amplitude or ICI was observed in Experiment 1. In contrast, MEP amplitude was significantly greater, and ICI significantly lower during the 'on' phase of imagined task performance in Experiment 2. These results are most likely related to the higher levels of target muscle activation required during actual task performance and the greater anatomical distance between target and control muscles in Experiment 2. These task characteristics may influence the observed degree of corticospinal excitability and ICI modulation.

Working memory and mental practice outcomes after stroke

OBJECTIVE

To examine the relationship between working memory and motor improvement obtained after a single training session combining mental and physical practice.

DESIGN

Before-after trial.

SETTING

Laboratory of a university-affiliated research rehabilitation center.

PARTICIPANTS

A sample of 12 patients with stroke and 14 age- and gender-matched healthy subjects.

INTERVENTION

In a single session, patients were trained with combined mental and physical practice to increase the loading on the affected leg while standing up and sitting down.

MAIN OUTCOME MEASURES

Motor improvement as measured by the percentage change in limb loading on the affected limb after training and 24 hours later (follow-up), and the relationship between working memory and percentage motor improvement.

RESULTS

The loading on the affected leg was improved after training (P< .01) and at follow-up (P< .05), and working memory scores at follow-up correlated significantly (P< .004 to P< .007) with the level of improvement. The visuospatial domain yielded the strongest correlation (r= .83), followed by the verbal (r= .62) and kinesthetic (r= .59) domains.

CONCLUSIONS

These results suggest that the outcome (improved limb loading) of mental rehearsal with motor imagery depends on the ability to maintain and manipulate information in working memory.

[New perspectives of locomotor rehabilitation after stroke]

The task-oriented approach incorporating treadmill walking for retraining gait early after stroke has contributed to promote locomotor recovery. To augment practice, training strategies such as mental practice and training in virtual environments are proposed. While the former offers more practice with less physical exertion, the latter allows safe practice in a variety of challenging environments. Work is under way to assess whether these new strategies can further enhance locomotor recovery.

Efeito da estratégia de simulação mental sobre o controle postural

A construção e manipulação espacial de imagens corporais têm origem basicamente visual e somato-motora. No entanto, a contribuição relativa de cada modalidade sensorial nos processos de simulação mental pode variar. Sirigu e Duhamel (2001) propuseram que a estratégia utilizada durante a simulação mental de movimentos produziria a ativação de circuitos neurais distintos. Neste estudo, investigamos o efeito da estratégia adotada na simulação mental de uma tarefa motora que envolve ajustes posturais utilizando as técnicas de cronometria mental e de estabilometria. Os voluntários, posicionados sobre uma plataforma de força vertical com os pés unidos e os olhos fechados, foram solicitados a realizar as seguintes tarefas: a) manter a postura ereta normal durante 20 segundos; b) contar mentalmente de um a 15; c) imaginar-se realizando o movimento de flexão plantar bilateral 15 vezes e d) executar o mesmo movimento por 15 vezes. Ao final do teste, relataram qual a estratégia utilizada para a realização da simulação mental. Com base no relato verbal foram então distinguidos em dois grupos: visuais e somato-motores. A análise da cronometria mental mostrou que o tempo utilizado para simular mentalmente os movimentos de flexão plantar não foi diferente daquele gasto durante a sua execução. Diferiu, porém, da condição contar para ambos os grupos. Para a análise estabilométrica, calculou-se um índice de simulação mental (ISM). Dos valores obtidos durante o imaginar, foram subtraídos os valores da condição contar, dividindo-se então a resultante pela soma dos dois. O grupo somato-motor apresentou índices positivos e significativamente diferentes do grupo visual para a área elíptica de deslocamento e amplitude de deslocamento no eixo ântero-posterior (y). Esses dados indicam um menor bloqueio da saída motora durante o imaginar de um movimento que envolve ajustes posturais no primeiro grupo. Essa diferença sugere que circuitos corticais e sub-corticais distintos serão ativados em função da estratégia adotada para simular mentalmente o movimento.

Mental practice: a promising restorative technique in stroke rehabilitation

Upper limb hemiparesis is a common, yet debilitating, result of stroke. It has long been known that mental practice, when combined with physical practice, improves motor learning and performance. Recent studies also indicate that massed use of the affected arm results in cortical reorganizations and correlative functional improvements. During mental practice, there are widespread activations of neural and muscular mechanisms as if the arm were actually being used. This article introduces mental practice as a form of massed practice, reviews the bases for mental practice as a potent restorative technique, and presents data suggesting mental practice as a restorative technique for upper limb hemiparesis.

Functional cerebral reorganization following motor sequence learning through mental practice with motor imagery

The goal of the present study was to examine, via positron emission tomography, the functional changes associated with the learning of a sequence of foot movements through mental practice with motor imagery (MI). Following intensive MI training over several days, which led to a modest but significant improvement in performance, healthy subjects showed an increase in activity restricted to the medial aspect of the orbitofrontal cortex (OFC), and a decrease in the cerebellum. These main results are largely consistent with those found in a previous study of sequence learning performed in our laboratory after physical practice of the same task [NeuroImage 16 (2002) 142]. Further analyses showed a positive correlation between the blood flow increase in the OFC and the percentage of improvement on the foot sequence task. Moreover, the increased involvement of the medial OFC revealed a modality specific anatomo-functional organization, as imagination of the sequential task after MI practice activated a more posterior region than its execution. These results demonstrate that learning a sequential motor task through motor imagery practice produces cerebral functional changes similar to those observed after physical practice of the same task. Moreover, the findings are in accord with the hypothesis that mental practice with MI, at least initially, improves performance by acting on the preparation and anticipation of movements rather than on execution per se.

Effects of imagery motor training on torque production of ankle plantar flexor muscles

The aim of this study was to investigate in control subjects the effect of imagery training on the torque of plantar-flexor muscles of the ankle. Twenty-nine subjects were allocated to one of three groups that performed either imagery training, low-intensity strength training, or no training (only measurements). The low-intensity training served as an attention control group. Plantar-flexor torques were measured before, during, directly after, and 4 weeks after the training period. At the end of a 7-week training program, significant differences were observed between the maximal voluntary torque production of the imagery training group (136.3 +/- 21.8% of pretraining torque) vs. the low-intensity training group (112.9 +/- 29.0%; P < 0.02) and the control group (113.6 +/- 19.2%; P < 0.02). The results of this study show that imagery training of lower leg muscles significantly increased voluntary torque production of the ankle plantar-flexor muscles and that the force increase was not due to nonspecific motivational effects. Such muscle strengthening effects might be beneficial in rehabilitation for improving or maintaining muscle torque after immobilization.

Motor imagery of phasic thumb abduction temporally and spatially modulates corticospinal excitability

OBJECTIVE

To explore the spatial and temporal characteristics of the modulation of corticospinal and segmental excitability during actual and imagined movement of a single digit.

METHODS

Using transcranial magnetic stimulation (TMS), motor evoked potentials (MEPs) were evoked in abductor pollicis brevis (APB) and abductor digiti minimi (ADM) of the dominant hand in 8 subjects, while they either rested, isometrically contracted their thenar muscles in time with a 1 Hz metronome, or imagined doing so. Magnetic stimuli were delivered during the 'on' and 'off' phases of the real and imagined movements. F waves were also recorded from APB and ADM under rest and motor imagery conditions.

RESULTS

It was found that both motor imagery and actual movement produced a muscle-specific, temporally modulated increase in corticospinal excitability during the task. The evidence of F-wave modulation was inconclusive.

CONCLUSIONS

These results lend further support to the notion that actual movement and motor imagery modulate corticospinal excitability in a similar manner, primarily at the supraspinal level.

SIGNIFICANCE

Motor imagery and actual movement appear to modulate motor cortex excitability with a similar degree of spatial and temporal resolution, which supports the use of motor imagery in the rehabilitation of motor function.

Brain activations during motor imagery of locomotor-related tasks: a PET study

Positron emission tomography (PET) was used to study the involvement of supraspinal structures in human locomotion. Six right-handed adults were scanned in four conditions while imagining locomotor-related tasks in the first person perspective: Standing (S), Initiating gait (IG), Walking (W) and Walking with obstacles (WO). When these conditions were compared to a rest (control) condition to identify the neural structures involved in the imagination of locomotor-related tasks, the results revealed a common pattern of activations, which included the dorsal premotor cortex and precuneus bilaterally, the left dorsolateral prefrontal cortex, the left inferior parietal lobule, and the right posterior cingulate cortex. Additional areas involving the pre-supplementary motor area (pre-SMA), the precentral gyrus, were activated during conditions that required the imagery of locomotor movements. Further subtractions between the different locomotor conditions were then carried out to determine the cerebral regions associated with the simulation of increasingly complex locomotor functions. These analyses revealed increases in rCBF activity in the left cuneus and left caudate when the W condition was compared to the IG condition, suggesting that the basal ganglia plays a role in locomotor movements that are automatic in nature. Finally, subtraction of the W from the WO condition yielded increases in activity in the precuneus bilaterally, the left SMA, the right parietal inferior cortex and the left parahippocampal gyrus. Altogether, the present findings suggest that higher brain centers become progressively engaged when demands of locomotor tasks require increasing cognitive and sensory information processing.

Motor learning produces parallel dynamic functional changes during the execution and imagination of sequential foot movements

The aim of the present positron emission tomography study was to measure the dynamic changes in cerebral activity before and after practice of an explicitly known sequence of foot movements when executed physically and to compare them to those elicited during motor imagery of the same movements. Nine healthy volunteers were scanned while performing both types of movement at an early phase of learning and after a 1-h training period of a sequence of dorsiflexions and plantarflexions with the left foot. These experimental conditions were compared directly, as well as to a perceptual control condition. Changes in regional cerebral blood flow associated with physical execution of the sequence early in the learning process were observed bilaterally in the dorsal premotor cortex and cerebellum, as well as in the left inferior parietal lobule. After training, however, most of these brain regions were no longer significantly activated, suggesting that they are critical for establishing the cognitive strategies and motor routines involved in executing sequential foot movements. By contrast, after practice, an increased level of activity was seen bilaterally in the medial orbitofrontal cortex and striatum, as well as in the left rostral portion of the anterior cingulate and a different region of the inferior parietal lobule, suggesting that these structures play an important role in the development of a long lasting representation of the sequence. Finally, as predicted, a similar pattern of dynamic changes was observed in both phases of learning during the motor imagery conditions. This last finding suggests that the cerebral plasticity occurring during the incremental acquisition of a motor sequence executed physically is reflected by the covert production of this skilled behavior using motor imagery.