Motor Imagery Condition Research Articles

Action observation facilitates motor cortical activity in patients with stroke and hemiplegia

Motor imagery (MI) is a mental practice that reproduces the visual- and/or kinesthetic-modality brain activations accompanying movement. It is a useful rehabilitation technique as the affected motor cortex can be stimulated in patients with stroke and hemiplegia. However, most patients with stroke have difficulty with MI owing to advanced age and/or higher-cognitive dysfunction, thus impairing their ability to internally simulate the action. We therefore investigated whether action observation (AO), an alternative form of motor stimulation that works via the mirror-neuron system, could facilitate motor cortical activity in such patients. Combined AO and physical training of the observed actions has been reported to have a positive impact on motor deficits after stroke. Eleven patients with stroke and hemiplegia affecting the hand performed MI and AO with verbal and video instructions under 19 channels of electroencephalogram (EEG) recording. The event-related desynchronization (ERD) was measured as an electroencephalographic marker of motor cortical activity. The ERD power in the AO condition (30.0±5.0%) was significantly higher than that in the MI condition (12.2±3.9%). These results suggest that AO could be a good option for patients with stroke who have difficulty using MI to effectively stimulate and reestablish cortical-peripheral motor pathways.

Target-directed motor imagery of the lower limb enhances event-related desynchronization.

Event-related desynchronization/synchronization (ERD/S) is an electroencephalogram (EEG) feature widely used as control signals for Brain-Computer Interfaces (BCIs). Nevertheless, the underlying neural mechanisms and functions of ERD/S are largely unknown, thus investigating them is crucial to improve the reliability of ERD/S-based BCIs. This study aimed to identify Motor Imagery (MI) conditions that enhance ERD/S. We investigated following three questions: 1) whether target-directed MI affects ERD/S, 2) whether MI with sound imagery affects ERD/S, and 3) whether ERD/S has a body part dependency of MI. Nine participants took part in the experiments of four MI conditions; they were asked to imagine right foot dorsiflexion (F), right foot dorsiflexion and the sound of a bass drum when the sole touched the floor (FS), right leg extension (L), and right leg extension directed toward a soccer ball (LT). Statistical comparison revealed that there were significant differences between conditions L and LT in beta-band ERD and conditions F and L in beta-band ERS. These results suggest that mental rehearsal of target-directed lower limb movement without real sensory stimuli can enhance beta-band ERD; furthermore, MI of foot dorsiflexion induces significantly larger beta-band ERS than that of leg extension. These findings could be exploited for the training of BCIs such as powered prosthetics for disabled person and neurorehabilitation system for stroke patients.

Effect of Motor Imagery After Motor Learning for 30 sec on Excitability of Spinal Neural Function and its Impact on Accurate Control of Muscle Force

This study aimed to examine the effects of motor imagery on the excitability of spinal neural function and accurate control of muscle force. In total, 30 healthy volunteers (15 men and 15 women; mean age, 21.1 ± 1.2 years) participated in the study. The methodology involved recording F-waves under resting conditions with a touching sensor. Also, the subjects learned to maintain the 50% maximum voluntary contraction (MVC) value of the pinch by viewing a meter display for 30 sec. Next, the pinch force was measured for 10 sec without using visual feedback (1st trial of pinch task). Subsequently, the subjects engaged in motor imagery and the F-waves were recorded. Finally, the pinch force was measured again, as in 1st trial of the pinch task (2nd trial of pinch task). In the control group, the subjects did not use motor imagery on similar processes as in the motor imagery condition phase from different days. F-waves were analyzed with persistence. Correction time and the 50% MVC error were calculated from the pinch force. Persistence was more increased under motor imagery than in the resting and touching sensor. In addition, no significant differences were observed in correction time and the 50% MVC error in the motor imagery group. But in the control group, correction time was decreased and the 50% MVC error was increased in the 2nd trial of pinch task as compared to the 1st trial. In conclusion, motor imagery after motor learning for 30 sec increased spinal neural excitability function. Moreover, motor imagery might allow accurate control and maintenance of muscle force.

The variety of methodology in Mirror Therapy practice for improving hand function after stroke

Abstract Many studies have shown that a repeated exercises in the mirror visual feedback and motor imagery conditions may help to restore a lasted hand function in stroke patients. The evidence of effectiveness of mirror therapy is promising but the use of this method varies widely within studies. It has been postulated that there is a need to formulate basic rules of mirror therapy application with respect to different stages of stroke or severity of hand paresis. In this article the review of methodological variability of applying mirror therapy to patients after stroke has been presented. The review highlights the benefit effect of mirror therapy on motor recovery and activities of daily living after stroke.

EEG and behavioural correlates of different forms of motor imagery during action observation in rhythmical actions

Recent studies show that participants can engage in motor imagery (MI) and action observation (AO) simultaneously (AO+MI), indicating a capacity for dual action simulation. Here we studied the electrophysiological correlates and behavioural outcomes of two forms of AO+MI, along with pure MI and pure AO control conditions. In synchronised AO+MI, participants imagined performing a rhythmical action in synchrony with an observed distractor action. In contrast in static AO+MI, where the imagery served to conflict with AO, participants imagined holding a static hand posture during AO. Following synchronised AO+MI, rhythmical execution was strongly biased toward the cycle time of the previously observed rhythm (‘imitation bias’), whereas a weaker bias was found following pure MI, and particularly for static AO+MI. In line with these findings, event-related desynchronisation (ERD) in primary sensorimotor and parietal regions was more pronounced in synchronised AO+MI compared to both pure AO and pure MI. These ERD amplitudes were, however, highly similar for static and synchronised AO+MI; suggesting that, regardless of co-represented content, both AO+MI states produced stronger motor activations than single action simulation. In contrast, synchronised AO+MI produced significantly stronger ERD in rostral prefrontal cortex compared to the other three conditions. This specific rostral prefrontal involvement most likely reflected additional cognitive processing for aligning dual action simulations. Together these results provide an important empirical validation of different AO+MI states, in that the imitation bias was strongly modulated by the content of the AO+MI instructions, and that synchronised AO+MI produced stronger behavioural and neurophysiological effects compared to pure AO or MI.

The Imagined Muscle Contraction Strengths did not affect the Changes of Spinal Motor Neurons Excitability

Background: Motor imagery can facilitate the spinal motor neurons excitability. However, it is unclear whether the imagined muscle contraction strengths affects the changes of spinal motor neurons excitability. Methods: The F-waves of the left thenar muscles were recorded in 10 healthy volunteers while the muscle was relaxed. In motor imagery trial, subjects imagined the thenar muscles activity at maximal voluntary contractions of 10%, 30%, 50%, and 70% while holding the sensor of the pinch meter; In post-imagery trial, immediately after motor imagery, the F-waves was recorded under resting. Results: Persistence and F/M amplitude ratio during motor imagery under all imagined muscle contraction strengths were significantly increased than at rest. However, there were no significant differences in the relative values of persistence, F/M amplitude ratio, and latency under all motor imagery conditions. Conclusions: Motor imagery under maximal voluntary contractions of 10%, 30%, 50%, and 70% can increase the spinal motor neurons excitability, but excitability does not vary with the imagined muscle contraction strengths.

Effect of motor imagery on excitability of spinal neural function and its impact on the accuracy of movement-considering the point at which subjects subjectively determine the 50%MVC point.

[Purpose] This study aimed to examine the effect of motor imagery on the accuracy of motion and the excitability of spinal neural function. [Subjects and Methods] Thirty healthy volunteers (males, 15; females, 15; mean age, 20.3 ± 1.0 years) were recruited. F-waves was recorded at rest, while holding a sensor, and while using motor imagery. Next, subjects learned 50% maximum voluntary contraction. The pinch force was measured without visual feedback before and after motor imagery. F-waves were analyzed with respect to persistence and the F/M amplitude ratio. Correction time and coefficient of variation were calculated from the pinch force. [Results] Persistence and F/M amplitude ratio ware significantly higher in the holding sensor and motor imagery conditions than in the resting condition. In addition, persistence under motor imagery was significantly higher than that in the holding sensor condition. No significant differences were observed in relative values of correction time and coefficient of variation between the two pinch action conditions. The pinch force in task 2 approximated a more authentic 50%MVC than that in task 1. [Conclusion] Motor imagery increases the excitability of spinal neural function, suggesting that it also affects accurate control of muscle force.

Virtual Reality-Guided Motor Imagery Increases Corticomotor Excitability in Healthy Volunteers and Stroke Patients.

ObjectiveTo investigate the effects of using motor imagery (MI) in combination with a virtual reality (VR) program on healthy volunteers and stroke patients. In addition, this study investigated whether task variability within the VR-guided MI programs would influence corticomotor excitability.MethodsThe present study included 15 stroke patients and 15 healthy right-handed volunteers who were presented with four different conditions in a random order: rest, MI alone, VR-guided MI, and VR-guided MI with task variability. The corticomotor excitability of each participant was assessed before, during, and after each condition by measuring changes in the various parameters of motor-evoked potentials (MEPs) of the extensor carpi radials (ECR). Changes in intracortical inhibition (ICI) and intracortical facilitation (ICF) were calculated after each condition as percentages of inhibition (%INH) and facilitation (%FAC) at rest.ResultsIn both groups, the increases in MEP amplitudes were greater during the two VR-guided MI conditions than during MI alone. Additionally, the reductions in ECR %INH in both groups were greater under the condition involving VR-guided MI with task variability than under that involving VR-guided MI with regular interval.ConclusionThe corticomotor excitability elicited by MI using a VR avatar representation was greater than that elicited by MI with real body observations. Furthermore, the use of task variability in a VR program may enhance neural regeneration after stroke by reducing ICI. The present findings support the use of various VR programs as well as the concept of combining MI with VR programs for neurorehabilitation.

MOTOR IMAGERY, PHYSICAL PRACTICE, AND MEMORY: THE EFFECTS ON PERFORMANCE AND WORKLOAD.

-The theoretical explanations used to explain changes in performance during motor imagery and physical practice conditions are inconsistent when memory retrieval is and is not required. This study measured performance time and workload during acquisition, a retention test requiring memory retrieval, and a retention test not requiring memory retrieval using a key-pressing task. The participants were assigned to physical practice with or without instructions to learn or motor imagery with or without instructions to learn. A diagram of the keys was presented during the practice trials and the first retention test, but was not presented during the second test. The results revealed no effect for the learning instructions or performance changes during the practice phases. However, during both retention tests participants in the physical practice conditions performed significantly faster than those in the motor imagery conditions. Also, higher levels of workload were reported for the motor imagery conditions when the retention test required memory retrieval compared to the other phases. A discussion of the implications of workload on performance is presented with respect to varying practice conditions.

Learning Recurrent Waveforms Within EEGs.

We demonstrate an algorithm to automatically learn the time-limited waveforms associated with phasic events that repeatedly appear throughout an electroencephalogram. To learn the phasic event waveforms we propose a multiscale modeling process that is based on existing shift-invariant dictionary learning algorithms. For each channel, waveforms at different temporal scales are learned based on the assumption that only a few waveforms occur in any window of the time-series, but the same waveforms reoccur throughout the signal. Once the waveforms are learned, the timing and amplitude of the phasic event occurrences are estimated using matching pursuit. To summarize the waveforms learned across multiple channels and subjects, we analyze their frequency content, their similarity to Gabor-Morlet wavelets, and perform shift-invariant k-means to cluster the waveforms. A prototype waveform from each cluster is then tested for differential spatial patterns between different motor imagery conditions. On multiple human EEG datasets, the learned waveforms capture key characteristics of signals they were trained to represent, with a consistency in waveform morphology and frequency content across multiple training sections and initializations. On multichannel datasets, the spatial amplitude patterns of the waveforms are also consistent and can be used to distinguish different modalities of motor imagery. We explored a methodology that can be used for modeling the recurrent waveforms in EEG traces. The methodology automatically identifies the most frequent phasic event waveforms in EEG, which could then be used as features for automatic evaluation and comparison of EEG during sleep, pathology, or mentally engaging tasks.

Study of motor and electrophysiological effects induced by the association of motor imagery exercises and Paired Associative Stimulation in 6 hemiplegic patients

Motor imagery (MI) is a cognitive process of imagining a movement without actually doing it. This technique has demonstrated its benefits in the rehabilitation of hemiplegic patients. Non-invasive brain stimulation (NIBS) is still at a preclinical stage but has demonstrated their adjunct effect in the learning of a motor task. In this study, we studied the motor and electrophysiological effects of a session combining Paired Associative Stimulation (PAS), a technique of NIBS and MI exercises (PAS-MI). A prospective, randomized cross-over study where six patients were included (4 men, age = 44.5 ± 13.7 years; 5.7 ± 7.7 months post-stroke). They randomly underwent three 15-minute sessions of stimulation, one week apart: PAS-MI, PAS alone and ShamPAS associated with MI exercises (ShamPAS-MI). The PAS intervention consisted in an electrical stimulation of the hemiplegic extensor carpi radialis (ECR) associated with cortical magnetic stimulation over the wrist motor area. In MI condition, the patient was instructed to imagine extension of his hemiplegic wrist and in ShamPAS intervention, we used a SHAM probe. We compared the surface variation of the motor-evoked potential (MEP) of the ECR and the amplitude of active extension (AE) of the hemiplegic side obtained after each session. Twenty-five minutes after the end of session PAS alone, an increase of MEP surface (+91% ± 150.3%) which reveals a higher cortical excitability associated with a slight motor improvement (ΔEA = 1.33 ± 3.14°) was shown. A smaller facilitation was shown after sessions PAS-MI and ShamPAS-MI (+45.97 ± 134.32% and 44.85 ± 28.77%, respectively) and, in these cases, was not associated with motor improvement. The session PAS alone seems to induce motor improvement associated with increased cortical excitability not shown after the other two sessions. The combination of two types of stimuli seems to have less effect, perhaps because of the mechanisms regulating the homeostasis of brain plasticity. The results have to be confirmed on a larger sample.

Modulation of ERD/S by having a conscious target during lower-extremity motor imagery.

In the field of neurorehabilitation with brain-computer interfaces (BCIs) technology, an EEG feature, event-related desynchronization/synchronization (ERD/S) caused by motor imagery (MI) is widely used for estimating human motor intention. However, sufficient neurofeedback training is required for the use of the MI-based BCI system, because the ability to generate ERD/S is highly dependent on individuals. To find an effective MI condition for the BCI system, we hypothesize that having a conscious target during MI would enhance the extent of ERD/S. In the experiments, we investigated the individual effect of two types of MIs: leg extension (L) and leg extension with a conscious target (i.e., kicking a ball (KB)) on the resultant ERD/S. We evaluated time-frequency maps of ERD/S and statistically compared these two conditions (i.e., L and KB). As a result, a significant difference was found in beta-ERD (paired t-test, p <; 0.01), while there were no significant differences in mu-ERD and beta-ERS. These results suggest that having a conscious target during lower extremity MI would strengthen the ERD in beta frequency band compared to the case without target.

Towards real-time visualization of a juggler’s brain

Surpassing the initial ‘wow’ effect of a complex juggling trick and producing long-lasting engaging performances are the main goals of any juggling act. Conveying to the audience the skill and the effort required for a performance is often difficult. In this paper, we use a wearable EEG headset to investigate how juggling skills can be inferred from a juggler’s brain. We observed characteristic brain activity and synchronization while juggling in both an expert and an intermediate juggler. We also found that processing of visuomotor skills and memory retention can be distinguished during motor imagery and simulated juggling conditions. For the first time, we were able to monitor a juggler’s brain in action. We have shown that using EEG while juggling could both improve our understanding of neuronal mechanisms governing visuomotor control and, importantly, represent a potential to enrich artistic performance and increase audience engagement.

Increased Prefrontal-Parietal EEG Gamma Band Correlation during Motor Imagery in Expert Video Game Players

Abstract. The aim of this study was to characterize the prefrontal-parietal EEG correlation in experienced video game players (VGPs) in relation to individuals with little or no video game experience (NVGPs) during a motor imagery condition for an action-type video game. The participants in both groups watched a first-person shooter (FPS) gameplay from Halo Reach during five minutes. None of the participants was notified as to the content of the video before watching it. Only the VGPs showed an increased right intrahemispheric prefrontal-parietal correlation (F4-P4) in the gamma band (31-50 Hz) during the observation of the gameplay. These data provide novel information on the participation of the gamma band during motor imagery for an action-type video game. It is probable that this higher degree of coupling between the prefrontal and parietalcortices could represent a characteristic pattern of brain functionality in VGPs as they make motor representations.

Similarities between explicit and implicit motor imagery in mental rotation of hands: An EEG study

Chronometric and imaging studies have shown that motor imagery is used implicitly during mental rotation tasks in which subjects for example judge the laterality of human hand pictures at various orientations. Since explicit motor imagery is known to activate the sensorimotor areas of the cortex, mental rotation is expected to do similar if it involves a form of motor imagery. So far, functional magnetic resonance imaging and positron emission tomography have been used to study mental rotation and less attention has been paid to electroencephalogram (EEG) which offers a high time-frequency resolution. The time-frequency analysis is an established method for studying explicit motor imagery. Although hand mental rotation is claimed to involve motor imagery, the time-frequency characteristics of mental rotation have never been compared with those of explicit motor imagery. In this study, time-frequency responses of EEG recorded during explicit motor imagery and during a mental rotation task, inducing implicit motor imagery, were compared. Fifteen right-handed healthy volunteers performed motor imagery of hands in one condition and hand laterality judgement tasks in another while EEG of the whole head was recorded. The hand laterality judgement was the mental rotation task used to induce implicit motor imagery. The time-frequency analysis and sLORETA localisation of the EEG showed that the activities in the sensorimotor areas had similar spatial and time-frequency characteristics in explicit motor imagery and implicit motor imagery conditions. Furthermore this sensorimotor activity was different for the left and for the right hand in both explicit and implicit motor imagery. This result supports that motor imagery is used during mental rotation and that it can be detected and studied with EEG technology. This result should encourage the use of mental rotation of body parts in rehabilitation programmes in a similar manner as motor imagery.

Excitability of spinal neural function during motor imagery in Parkinson�s disease

the median nerve at the wrist in subjects during two motor imagery conditions: holding and not holding the sensor of a pinch meter between the thumb and index finger. Our aim was to determine whether mental simulation without the muscle contraction associated with motion can increase the excitability of spinal neural function in patients with Parkinson's disease (PD). F-waves of the left thenar muscles were examined in 10 patients with PD under resting, holding and motor imagery conditions. For the holding condition, the subjects held the sensor of the pinch meter between their thumb and index finger. For the motor imagery conditions, the subjects were asked to imagine a 50% maximal voluntary isometric contraction holding and not holding the sensor of the pinch meter between their thumb and index finger (motor imagery "with"/"without sensor"). Persistence during motor imagery under the "with sensor" condition increased significantly compared with persistence during resting (n=10, z=2.2509, p=0.0244, Wilcoxon test). The F/M amplitude ratio during motor imagery under the "with sensor" condition increased significantly compared with that during resting (n=10, z=2.1915, p=0.0284, Wilcoxon test). Excitability of spinal neural function during motor imagery in Parkinson's disease Motor imagery under the "with the sensor" condition increased excitability of the spinal neural output to the thenar muscles. Because excitability of the spinal neural output to the thenar muscles during motor imagery "with the sensor" was significantly higher than that during resting, we suggest that movement preparation for a motor imagery task is important in patients with PD.

Motor imagery and electrical stimulation reproduce corticospinal excitability at levels similar to voluntary muscle contraction.

BackgroundThe combination of voluntary effort and functional electrical stimulation (ES) appears to have a greater potential to induce plasticity in the motor cortex than either electrical stimulation or voluntary training alone. However, it is not clear whether the motor commands from the central nervous system, the afferent input from peripheral organs, or both, are indispensable to induce the facilitative effects on cortical excitability. To clarify whether voluntary motor commands enhance corticospinal tract (CoST) excitability during neuromuscular ES, without producing voluntary muscular contraction (VMC), we examined the effect of a combination of motor imagery (MI) and electrical muscular stimulation on CoST excitability using transcranial magnetic stimulation (TMS).MethodsEight neurologically healthy male subjects participated in this study. Five conditions (resting, MI, ES, ES + MI [ESMI], and VMC) were established. In the ES condition, a 50-Hz stimulus was applied for 3 to 5 s to the first dorsal interosseous (FDI) while subjects were relaxed. In the MI condition, subjects were instructed to imagine abducting their index finger. In the ESMI condition, ES was applied approximately 1 s after the subject had begun to imagine index finger abduction. In the VMC condition, subjects modulated the force of index finger abduction to match a target level, which was set at the level produced during the ES condition. TMS was applied on the hotspot for FDI, and the amplitude and latency of motor evoked potentials (MEPs) were measured under each condition.ResultsMEP amplitudes during VMC and ESMI were significantly larger than those during other conditions; there was no significant difference in MEP amplitude between these 2 conditions. The latency of MEPs evoked during MI and VMC were significantly shorter than were those evoked during rest and ES.ConclusionsMEP acutely reinforced in ESMI may indicate that voluntary motor drive markedly contributes to enhance CoST excitability, without actual muscular contraction.

Excitability of spinal neural function during several motor imagery tasks involving isometric opponens pollicis activity

It is unclear whether mental simulation without actual muscle contraction associated with actual motion can increase the excitability of the spinal neural function. To determine the best method for mental simulation without actual muscle contraction, we analyzed the F-wave of thenar muscles after stimulating the median nerve by motor imagery whilst holding the sensor of a pinch meter between the thumb and index finger and without holding the sensor. Healthy volunteers (n = 11; mean age, 34 years) participated in this study after providing informed consent. We examined the F-wave of the left thenar muscles after stimulating the left median nerve at the wrist at rest and under holding and motor imagery conditions. For the motor imagery condition, the subjects were asked to establish 50% maximal voluntary contraction (MVC) of isometric contraction while holding the sensor between the thumb and index finger (motor imagery with the sensor condition) and without holding the sensor on another day (motor imagery without the sensor condition). The persistence and amplitude ratio of F/M during motor imagery with or without the sensor was better than that during relaxation. In particular, this ratio was significantly higher under the with sensor condition than under the without sensor condition. Movement preparation for a motor imagery task involving 50% MVC isometric contraction of the opponens pollicis is important.

Activation of thalamus in motor imagery results from gating by hypnosis

The ability to mentally imagine the performance of automatic movements has been well-established being employed in sports and physiotherapy as a tool for motor learning and rehabilitation. This is probably mediated by engagement of the same brain areas as during real motor performance. Here we investigated the effect of hypnotic trance on the cerebral activation pattern engaged in motor imagery in 16 healthy, right-handed subjects using fMRI. Motor imagery as compared with rest was related to activations in the left medial frontal areas (preSMA/SMA), prefrontal- and frontal areas, putamen and inferior parietal areas. When compared with performance of the same movements motor imagery resulted in activation of the left middle frontal cortex, precuneus, and posterior cingulate. Under hypnotic trance there was one extra-activation in the left thalamus which occurred specifically in the motor imagery condition. The regional beta indices were highly correlated among the areas of the cortical-subcortical motor network. Our data accord with the notion that hypnotic trance enhances the motor control circuit engaged in motor imagery by modulating the gating function of the thalamus.

Acquiring functional object knowledge through motor imagery?

A widely investigated question in the research on the acquisition of novel functional object representations is the role of the action system. Whereas most studies so far have investigated the role of active action training on the acquisition of object representation, we investigated whether people are able to acquire object representations by just imagining the use of novel objects, given that previous findings suggested that executed and imagined actions share a common representational format. To this end, participants trained the use of novel objects in a motor imagery condition. Training comprised the particular grip applied to the objects and the objects' typical end location. Subsequently, participants' object representations were assessed by means of an object detection task. The results show that participants responded slower when the novel objects were presented at functionally incorrect end locations, indicating that the participants had acquired functional knowledge about object use. Yet, there was no effect of correct versus incorrect grip. Altogether, the findings suggest that motor imagery can facilitate the acquisition of novel object representations, but point also to differences between first-hand action training and training by imagery.