Event-related potentials as a function of movement parameter variations during motor imagery and isometric action

A case for hybrid BCIs: combining optical and electrical modalities improves accuracy

Near-infrared spectroscopy (NIRS) is a promising research tool that found its way into the field of brain-computer interfacing (BCI). BCI is crucially dependent on maximized usability thus demanding lightweight, compact, and low-cost hardware. We designed, built, and validated a hybrid BCI system incorporating one optical and two electrical modalities ameliorating usability issues. The novel hardware consisted of a NIRS device integrated with an electroencephalography (EEG) system that used two different types of electrodes: Regular gelled gold disk electrodes and tri-polar concentric ring electrodes (TCRE). BCI experiments with 16 volunteers implemented a two-dimensional motor imagery paradigm in off- and online sessions. Various non-canonical signal processing methods were used to extract and classify useful features from EEG, tEEG (EEG through TCRE electrodes), and NIRS. Our analysis demonstrated evidence of improvement in classification accuracy when using the TCRE electrodes compared to disk electrodes and the NIRS system. Based on our synchronous hybrid recording system, we could show that the combination of NIRS-EEG-tEEG performed significantly better than either single modality only.

A solution to supervised motor imagery task in the BCI Controlled Robot Contest in World Robot Contest

Background:

One of the most prestigious competitions in the world is the World Robot Conference. This paper presents the winning solution to the supervised motor imagery (MI) task in the BCI Controlled Robot Contest in World Robot Contest 2021.

Methods:

Data augmentation, preprocessing, feature extraction, and model training are the main components of the solution. The model is based on EEGNet, a popular convolutional neural networks model for classifying electroencephalography data.

Results:

Despite the model’s lack of stability, this solution was the most successful in the task. The channels closest to the vertex were the most helpful in feature extraction.

Conclusion:

This solution is suitable for supervised MI tasks not only in this competition but also in future scenarios.

The Inhibition Effect of Affordances in Action Picture Naming: An ERP Study

How quickly are different kinds of conceptual knowledge activated in action picture naming? Using a masked priming paradigm, we manipulated the prime category type (artificial vs. natural), prime action type (precision, power, vs. neutral grip), and target action type (precision vs. power grip) in action picture naming, while electrophysiological signals were measured concurrently. Naming latencies showed an inhibition effect in the congruent action type condition compared with the neutral condition. ERP results showed that artificial and natural category primes induced smaller waveforms in precision or power action primes than neutral primes in the time window of 100-200 msec. Time-frequency results consistently presented a power desynchronization of the mu rhythm in the time window of 0-210 msec with precision action type artificial objects compared with neutral primes, which localized at the supplementary motor, precentral and postcentral areas in the left hemisphere. These findings suggest an inhibitory effect of affordances arising at conceptual preparation in action picture naming and provide evidence for embodied cognition.

Induction of plasticity in the human motor system by motor imagery and transcranial magnetic stimulation

KEY POINTS

Delivering transcranial magnetic brain stimulation over the motor cortex during motor imagination leads to enhanced motor output, which is selective for the muscles primarily involved in the imagined movement. This novel protocol may be useful to enhance function after damage to the motor system, such as after stroke.

ABSTRACT

Several paired stimulation paradigms are known to induce plasticity in the motor cortex, reflected by changes in the motor evoked potential (MEP) following the paired stimulation. Motor imagery (MI) is capable of activating the motor system and affecting cortical excitability. We hypothesized that it might be possible to use MI in conjunction with transcranial magnetic stimulation (TMS) to induce plasticity in the human motor system. TMS was delivered to the motor cortex of healthy human subjects, and baseline MEPs recorded from forearm flexor, forearm extensor and intrinsic hand muscles. Subjects were then asked to imagine either wrist flexion or extension movements during TMS delivery (n = 90 trials). Immediately after this intervention, MEP measurement was repeated. Control protocols tested the impact of imagination or TMS alone. Flexion imagination with TMS increased MEPs in flexors and an intrinsic hand muscle. Extensor imagination with TMS increased MEPs in extensor muscles only. The control paradigms did not produce significant changes. We conclude that delivering TMS during MI is capable of inducing plastic changes in the motor system. This new protocol may find utility to enhance functional rehabilitation after brain injury.

Attempted Arm and Hand Movements can be Decoded from Low-Frequency EEG from Persons with Spinal Cord Injury

We show that persons with spinal cord injury (SCI) retain decodable neural correlates of attempted arm and hand movements. We investigated hand open, palmar grasp, lateral grasp, pronation, and supination in 10 persons with cervical SCI. Discriminative movement information was provided by the time-domain of low-frequency electroencephalography (EEG) signals. Based on these signals, we obtained a maximum average classification accuracy of 45% (chance level was 20%) with respect to the five investigated classes. Pattern analysis indicates central motor areas as the origin of the discriminative signals. Furthermore, we introduce a proof-of-concept to classify movement attempts online in a closed loop, and tested it on a person with cervical SCI. We achieved here a modest classification performance of 68.4% with respect to palmar grasp vs hand open (chance level 50%).

EEG Brain Activity in Dynamic Health Qigong Training: Same Effects for Mental Practice and Physical Training?

In recent years, there has been significant uptake of meditation and related relaxation techniques, as a means of alleviating stress and fostering an attentive mind. Several electroencephalogram (EEG) studies have reported changes in spectral band frequencies during Qigong meditation indicating a relaxed state. Much less is reported on effects of brain activation patterns induced by Qigong techniques involving bodily movement. In this study, we tested whether (1) physical Qigong training alters EEG theta and alpha activation, and (2) mental practice induces the same effect as a physical Qigong training. Subjects performed the dynamic Health Qigong technique Wu Qin Xi (five animals) physically and by mental practice in a within-subjects design. Experimental conditions were randomized. Two 2-min (eyes-open, eyes-closed) EEG sequences under resting conditions were recorded before and immediately after each 15-min exercise. Analyses of variance were performed for spectral power density data. Increased alpha power was found in posterior regions in mental practice and physical training for eyes-open and eyes-closed conditions. Theta power was increased after mental practice in central areas in eyes-open conditions, decreased in fronto-central areas in eyes-closed conditions. Results suggest that mental, as well as physical Qigong training, increases alpha activity and therefore induces a relaxed state of mind. The observed differences in theta activity indicate different attentional processes in physical and mental Qigong training. No difference in theta activity was obtained in physical and mental Qigong training for eyes-open and eyes-closed resting state. In contrast, mental practice of Qigong entails a high degree of internalized attention that correlates with theta activity, and that is dependent on eyes-open and eyes-closed resting state.

Effect of Mental Imagery on the Development of Skilled Motor Actions

To test the effect of imagery in the training of skilled movements, an experiment was designed in which athletes learned a new motor action and trained themselves for a month either by overt action or by mental imagery of the action. The experiment was carried out with 30 male karateka ( M age = 35 yr., SD = 8.7; M years of practice = 6, SD = 3) instructed to perform an action ( Ura-Shuto-Uchi) that they had not previously learned. The athletes were divided into three groups: Untrained (10 subjects who did not perform any training), Action Trained (10 subjects who performed Ura-Shuto-Uchi training daily for 16 minutes), and Mental Imagery (10 subjects who performed mental imagery training of Ura-Shuto-Uchi daily for 16 minutes). The subjects were tested five times, once every 7 days. During each test, they performed a series of 60 motor action trials. In Tests 1, 3, and 5, they also performed a series of 60 mental imagery trials. During the trials, an electroencephalogram (EEG), electromyography (EMG), muscle strength and power, and other physiological parameters were recorded. The results differed by group. Untrained subjects did not show significant effects. In the Action Trained group, training had an effect on reactivity and movement speed, with a reduction of EMG activation and reaction times. Moreover, muscle strength, power, and work increased significantly. The Mental Imagery group showed the same effects on muscle strength, power, and work, but changes in reactivity were not observed. In the Mental Imagery group, the study of Movement Related Brain Macropotentials indicated a progressive modification of the profile of the waves from Test 1 to Test 5 during imagery, showing significant variations of the amplitude of the waves related to the premotor and motor execution periods. Results show that motor imagery can influence muscular abilities such as strength and power and can modify Movement Related Brain Macropotentials, the profile of which potentially could be used to verify the effectiveness of motor imagery training.

Modeling Human Transcription Typing with Queuing Network-Model Human Processor (QN-MHP)

Typing is one of the basic and prevalent activities in human machine interaction. John (1988, 1996) proposed a PERT (Project-Evaluation-Research-Technique)-based model called TYPIST, which modeled 21 of the 31 behavioral phenomena in transcription typing (Salthouse, 1986, 1987; Gentner, 1983). However, TYPIST can only analyze the typing phenomena along the time dimension; it can not model error and eye movement of typing. Based on the queuing network theory of human performance (Liu, 1996, 1997) and current discoveries in brain and cognitive sciences, this paper proposes a queuing network model of typing which successfully modeled not only all the 21 phenomena modeled by TYPIST, but also 13 additional phenomena in transcription typing including 5 typing error phenomena, 3 eye movement phenomena and 2 brain imaging phenomena. Further developments of the queuing network model in modeling typing and other tasks, and its value in proactive ergonomic design of typing interfaces are discussed.

Long-Lasting Cortical Reorganization as the Result of Motor Imagery of Throwing a Ball in a Virtual Tennis Court

In order to characterize the neural signature of a motor imagery (MI) task, the present study investigates for the first time the oscillation characteristics including both of the time-frequency measurements, event related spectral perturbation and intertrial coherence (ITC) underlying the variations in the temporal measurements (event related potentials, ERP) directly related to a MI task. We hypothesize that significant variations in both of the time-frequency measurements underlie the specific changes in the ERP directly related to MI. For the MI task, we chose a simple everyday task (throwing a tennis ball), that does not require any particular motor expertise, set within the controlled virtual reality scenario of a tennis court. When compared to the rest condition a consistent, long-lasting negative fronto-central ERP wave was accompanied by significant changes in both time frequency measurements suggesting long-lasting cortical activity reorganization. The ERP wave was characterized by two peaks at about 300 ms (N300) and 1000 ms (N1000). The N300 component was centrally localized on the scalp and was accompanied by significant phase consistency in the delta brain rhythms in the contralateral central scalp areas. The N1000 component spread wider centrally and was accompanied by a significant power decrease (or event related desynchronization) in low beta brain rhythms localized in fronto-precentral and parieto-occipital scalp areas and also by a significant power increase (or event related synchronization) in theta brain rhythms spreading fronto-centrally. During the transition from N300 to N1000, a contralateral alpha (mu) as well as post-central and parieto-theta rhythms occurred. The visual representation of movement formed in the minds of participants might underlie a top-down process from the fronto-central areas which is reflected by the amplitude changes observed in the fronto-central ERPs and by the significant phase synchrony in contralateral fronto-central delta and contralateral central mu to parietal theta presented here.

Excitability of spinal motor neurons during motor imagery of thenar muscle activity under maximal voluntary contractions of 50% and 100

[Purpose] We often perform physical therapy using motor imagery of muscle contraction to improve motor function for healthy subjects and central nerve disorders. This study aimed to determine the differences in the excitability of spinal motor neurons during motor imagery of a muscle contraction at different contraction strengths. [Subjects] We recorded the F-wave in 15 healthy subjects. [Methods] In resting trial, the muscle was relaxed during F-wave recording. For motor imagery trial, subjects were instructed to imagine maximal voluntary contractions of 50% and 100% while holding the sensor of a pinch meter, and F-waves were recorded for each contraction. The F-wave was recorded immediately after motor imagery. [Results] Persistence and F/M amplitude ratio during motor imagery under maximal voluntary contractions of 50% and 100% were significantly higher than that at rest. In addition, the relative values of persistence, F/M amplitude ratio, and latency were similar during motor imagery under the two muscle contraction strengths. [Conclusion] Motor imagery under maximal voluntary contractions of 50% and 100% can increase the excitability of spinal motor neurons. Differences in the imagined muscle contraction strengths are not involved in changes in the excitability of spinal motor neurons.

Influence of motor imagery of isometric opponens pollicis activity on the excitability of spinal motor neurons: a comparison using different muscle contraction strengths

[Purpose] This study aimed to determine the differences in the excitability of spinal motor neurons during motor imagery of a muscle contraction at different contraction strengths. [Methods] We recorded the F-wave in 15 healthy subjects. First, in a trial at rest, the muscle was relaxed during F-wave recording. Next, during motor imagery, subjects were instructed to imagine maximum voluntary contractions of 10%, 30%, and 50% while holding the sensor of a pinch meter, and F-waves were recorded for each contraction. F-waves were recorded immediately and at 5, 10, and 15 min after motor imagery. [Results] Both persistence and F/M amplitude ratios during motor imagery under maximum voluntary contractions of 10%, 30%, and 50% were significantly higher than that at rest. In addition, persistence, F/M amplitude ratio, and latency were similar during motor imagery under the three muscle contraction strengths. [Conclusion] Motor imagery under maximum voluntary contractions of 10%, 30%, and 50% can increase the excitability of spinal motor neurons. The results indicated that differences in muscle contraction strengths during motor imagery are not involved in changes in the excitability of spinal motor neurons.

Neurophysiological correlates of visuo-motor learning through mental and physical practice

We have previously shown that mental rehearsal can replace up to 75% of physical practice for learning a visuomotor task (Allami, Paulignan, Brovelli, & Boussaoud, (2008). Experimental Brain Research, 184, 105-113). Presumably, mental rehearsal must induce brain changes that facilitate motor learning. We tested this hypothesis by recording scalp electroencephalographic activity (EEG) in two groups of subjects. In one group, subjects executed a reach to grasp task for 240 trials. In the second group, subjects learned the task through a combination of mental rehearsal for the initial 180 trials followed by the execution of 60 trials. Thus, one group physically executed the task for 240 trials, the other only for 60 trials. Amplitudes and latencies of event-related potentials (ERPs) were compared across groups at different stages during learning. We found that ERP activity increases dramatically with training and reaches the same amplitude over the premotor regions in the two groups, despite large differences in physically executed trials. These findings suggest that during mental rehearsal, neuronal changes occur in the motor networks that make physical practice after mental rehearsal more effective in configuring functional networks for skilful behaviour.

EEG signatures of arm isometric exertions in preparation, planning and execution

The electroencephalographic (EEG) activity patterns in humans during motor behaviour provide insight into normal motor control processes and for diagnostic and rehabilitation applications. While the patterns preceding brisk voluntary movements, and especially movement execution, are well described, there are few EEG studies that address the cortical activation patterns seen in isometric exertions and their planning. In this paper, we report on time and time-frequency EEG signatures in experiments in normal subjects (n=8), using multichannel EEG during motor preparation, planning and execution of directional centre-out arm isometric exertions performed at the wrist in the horizontal plane, in response to instruction-delay visual cues. Our observations suggest that isometric force exertions are accompanied by transient and sustained event-related potentials (ERP) and event-related (de-)synchronisations (ERD/ERS), comparable to those of a movement task. Furthermore, the ERPs and ERD/ERS are also observed during preparation and planning of the isometric task. Comparison of ear-lobe-referenced and surface Laplacian ERPs indicates the contribution of superficial sources in supplementary and pre-motor (FC(z)), parietal (CP(z)) and primary motor cortical areas (C₁ and FC₁) to ERPs (primarily negative peaks in frontal and positive peaks in parietal areas), but contribution of deep sources to sustained time-domain potentials (negativity in planning and positivity in execution). Transient and sustained ERD patterns in μ and β frequency bands of ear-lobe-referenced and surface Laplacian EEG indicate the contribution of both superficial and deep sources to ERD/ERS. As no physical displacement happens during the task, we can infer that the underlying mechanisms of motor-related ERPs and ERD/ERS patterns do not only depend on change in limb coordinate or muscle-length-dependent ascending sensory information and are primary generated by motor preparation, direction-dependent planning and execution of isometric motor tasks. The results contribute to our understanding of the functions of different brain regions during voluntary motor tasks and their activity signatures in EEG can shed light on the relationships between large-scale recordings such as EEG and other recordings such as single unit activity and fMRI in this context.

Comparison of movement related cortical potential in healthy people and amyotrophic lateral sclerosis patients

Objective: To understand the brain motor functions and neurophysiological changes due to motor disorder by comparing electroencephalographic data between healthy people and amyotrophic lateral sclerosis (ALS) patients.

Methods: The movement related cortical potential (MRCP) was recorded from seven healthy subjects and four ALS patients. They were asked to imagine right wrist extension at two speeds (fast and slow). The peak negativity (PN) and rebound rate (RR) were extracted from MRCP for comparison.

Results: The statistical analysis has showed that there was no significant difference in PN between the healthy and the ALS subjects. However, the healthy subjects presented faster RR than ALS during both fast and slow movement imagination.

Conclusions: The weaker RR of ALS patients might reflect the impairment of motor output pathways or the degree of motor degeneration.

Significance: The comparison between healthy people and ALS patients provides a way to explain the movement disorder through brain electrical signal. In addition, the characteristics of MRCP could be used to monitor and guide brain plasticity in patients.

Electrophysiological indicators of visuomotor planning: delay-dependent changes

A visuomotor task was used to investigate the influence of a varying response delay on the evoked activity measured during motor planning. Participants performed one-dimensional hand movements to visual targets after 200-, 1,000-, and 5,000- msec. delays with respect to the target offset. In response to an imperative go signal, similar deflections were observed over motor areas in all delay conditions. In contrast, activity at posterior electrodes was strongly delay-dependent. During the shortest delay condition, evoked alpha oscillations were pronounced at occipitoparietal recording sites and were accompanied by P300-like positive waves. In contrast, when the delay was either 1,000 or 5,000 msec., lateral occipitotemporal deflections (N1) were observed. Also, during the longest delay condition another P300-like component was measured, which was entirely absent when the delay was 1,000 msec. These results suggest that neurophysiological processes underlie motor planning, change depending on the time of response.

Disentangling motor execution from motor imagery with the phantom limb

Amputees can move their phantom limb at will. These 'movements without movements' have generally been considered as motor imagery rather than motor execution, but amputees can in fact perform both executed and imagined movements with their phantom and they report distinct perceptions during each task. Behavioural evidence for this dual ability comes from the fact that executed movements are associated with stump muscle contractions whereas imagined movements are not, and that phantom executed movements are slower than intact hand executed movements whereas the speed of imagined movements is identical for both hands. Since neither execution nor imagination produces any visible movement, we hypothesized that the perceptual difference between these two motor tasks relies on the activation of distinct cerebral networks. Using functional magnetic resonance imaging and changes in functional connectivity (dynamic causal modelling), we examined the activity associated with imagined and executed movements of the intact and phantom hands of 14 upper-limb amputees. Distinct but partially overlapping cerebral networks were active during both executed and imagined phantom limb movements (both performed at the same speed). A region of interest analysis revealed a 'switch' between execution and imagination; during execution there was more activity in the primary somatosensory cortex, the primary motor cortex and the anterior lobe of the cerebellum, while during imagination there was more activity in the parietal and occipital lobes, and the posterior lobe of the cerebellum. In overlapping areas, task-related differences were detected in the location of activation peaks. The dynamic causal modelling analysis further confirmed the presence of a clear neurophysiological distinction between imagination and execution, as motor imagery and motor execution had opposite effects on the supplementary motor area-primary motor cortex network. This is the first imaging evidence that the neurophysiological network activated during phantom limb movements is similar to that of executed movements of intact limbs and differs from the phantom limb imagination network. The dual ability of amputees to execute and imagine movements of their phantom limb and the fact that these two tasks activate distinct cortical networks are important factors to consider when designing rehabilitation programmes for the treatment of phantom limb pain.

Brain plasticity in the motor network is correlated with disease progression in amyotrophic lateral sclerosis

OBJECTIVE

To test the influence of functional cerebral reorganization in amyotrophic lateral sclerosis (ALS) on disease progression.

METHODS

Nineteen predominantly right-handed ALS patients and 21 controls underwent clinical evaluation, functional Magnetic Resonance Imaging (fMRI), and diffusion tensor imaging. Patients were clinically re-evaluated 1 year later and followed until death. For fMRI, subjects executed and imagined a simple hand-motor task. Between-group comparisons were performed, and correlations were searched with motor deficit arm Medical Research Council (MRC) score, disease progression ALS Functional Rating Scale (ALSFRS), and survival time.

RESULTS

By the MRC score, the hand strength was lowered by 12% in the ALS group predominating on the right side in accordance with an abnormal fractional anisotropy (FA) limited to the left corticospinal tract (37.3% reduction vs. controls P < 0.01). Compared to controls, patients displayed overactivations in the controlateral parietal (P < 0.004) and somatosensory (P < 0.004) cortex and in the ipsilateral parietal (P < 0.01) and somatosensory (P < 0.01) cortex to right-hand movement. Movement imagination gave similar results while no difference occurred with left-hand tasks. Stepwise regression analysis corrected for multiple comparisons showed that controlateral parietal activity was inversely correlated with disease progression (R(2) = 0.43, P = 0.001) and ipsilateral somatosensory activations with the severity of the right-arm deficit (R(2) = 0.48, P = 0.001).

CONCLUSIONS

Cortical Blood Oxygen Level Dependent (BOLD) signal changes occur in the brain of ALS patients during a simple hand-motor task when the motor deficit is still moderate. It is correlated with the rate of disease progression suggesting that brain functional rearrangement in ALS may have prognostic implications.

Befunde aus EEG-Untersuchungen zum Mentalen Training

Mentales Training (MT) im Sinne der planmäßig wiederholten Vorstellung eines Bewegungsablaufes ist ein zentraler Gegenstand sportpsychologischer Forschung. Im Hochleistungssport und in der Rehabilitation wird es zur Optimierung von Bewegungen eingesetzt. Einen Erklärungsansatz der Trainingswirkung bietet die Simulationstheorie mit dem zentralen Postulat, dass Bewegungsausführung und -vorstellung gleiche neuronale Strukturen aktivieren (funktionale Äquivalenz). Diese Annahme wurde mittels verschiedener neurophysiologischer Methoden geprüft, die teils zu widersprüchlichen Befunden führten. Die Elektroenzephalographie (EEG) kann unserer Ansicht nach dabei helfen, Lücken im theoretischen Erkenntnisprozess zu schließen. In diesem Artikel geben wir einen Überblick über die aktuelle Befundlage zum Mentalen Training mittels EEG. Es sollen drei wesentliche Vorteile der Methode aufgezeigt werden: (a) das EEG liefert Maße der neurophysiologischen Aktivität mit hoher zeitlicher Auflösung, (b) technische Weiterentwicklungen (drahtlose Hardware, tragbare Ausrüstung) erlauben die notwendige Bewegungsfreiheit für eine Anwendung im Sportkontext und (c) in der Rehabilitation kann die Vorstellung von Bewegungen als mentale Strategie dienen, um eine Neuroprothese auf Basis von Hirnsignalen zu steuern.

Re-imagining motor imagery: building bridges between cognitive neuroscience and sport psychology

One of the most remarkable capacities of the mind is its ability to simulate sensations, actions, and other types of experience. A mental simulation process that has attracted recent attention from cognitive neuroscientists and sport psychologists is motor imagery or the mental rehearsal of actions without engaging in the actual physical movements involved. Research on motor imagery is important in psychology because it provides an empirical window on consciousness and movement planning, rectifies a relative neglect of non-visual types of mental imagery, and has practical implications for skill learning and skilled performance in special populations (e.g., athletes, surgeons). Unfortunately, contemporary research on motor imagery is hampered by a variety of semantic, conceptual, and methodological issues that prevent cross-fertilization of ideas between cognitive neuroscience and sport psychology. In this paper, we review these issues, suggest how they can be resolved, and sketch some potentially fruitful new directions for inter-disciplinary research in motor imagery.

Strength gains by motor imagery with different ratios of physical to mental practice

The purpose of this training study was to determine the magnitude of strength gains following a high-intensity resistance training (i.e., improvement of neuromuscular coordination) that can be achieved by imagery of the respective muscle contraction imagined maximal isometric contraction (IMC training). Prior to the experimental intervention, subjects completed a 4-week standardized strength training program. 3 groups with different combinations of real maximum voluntary contraction (MVC) and mental (IMC) strength training (M75, M50, M25; numbers indicate percentages of mental trials) were compared to a MVC-only training group (M0) and a control condition without strength training (CO). Training sessions (altogether 12) consisted of four sets of two maximal 5-s isometric contractions with 10 s rest between sets of either MVC or IMC training. Task-specific effects of IMC training were tested in four strength exercises commonly used in practical settings (bench pressing, leg pressing, triceps extension, and calf raising). Maximum isometric voluntary contraction force (MVC) was measured before and after the experimental training intervention and again 1 week after cessation of the program. IMC groups (M25, M50, M75) showed slightly smaller increases in MVC (3.0% to 4.2%) than M0 (5.1%), but significantly stronger improvements than CO (−0.2%). Compared to further strength gains in M0 after 1 week (9.4% altogether), IMC groups showed no “delayed” improvement, but the attained training effects remained stable. It is concluded that high-intensity strength training sessions can be partly replaced by IMC training sessions without any considerable reduction of strength gains.

Identification of task parameters from movement-related cortical potentials

The study investigates the accuracy in discriminating rate of torque development (RTD) and target torque (TT) (task parameters) from electroencephalography (EEG) signals generated during imaginary motor tasks. Signals were acquired from nine healthy subjects during four imaginary isometric plantar-flexions of the right foot involving two RTDs (ballistic and moderate) and two TTs (30 and 60% of the maximal voluntary contraction torque), each repeated 60 times in random order. The single-trial EEG traces were classified with a pattern recognition approach based on wavelet coefficients as features and support vector machine (SVM) as classifier. Average misclassification rates were (mean +/- SD) 16 +/- 9% and 26 +/- 13% for discrimination of the two TTs under ballistic and moderate RTDs, respectively. RTDs could be discriminated with misclassification rates of 16 +/- 11% and 19 +/- 10% under high and low TT, respectively. These results indicate that differences in both TT and RTD can be detected from single-trial EEG traces during imaginary tasks.

EEG changes during sequences of visual and kinesthetic motor imagery

The evoked cerebral electric response when sequences of complex motor imagery (MI) task are executed several times is still unclear. This work aims at investigating the existence of habituation in the cortical response, more specifically in the alpha band peak of parietal and occipital areas (10-20 international system electroencephalogram, EEG, protocol). The EEG signals were acquired during sequences of MI of volleyball spike movement in kinesthetic and visual modalities and also at control condition. Thirty right-handed male subjects (18 to 40 years) were assigned to either an 'athlete' or a 'non-athlete' group, both containing 15 volunteers. Paired Wilcoxon tests (with α=0.05) indicates that sequential MI of complex tasks promotes cortical changes, mainly in the power vicinity of the alpha peak. This finding is more pronounced along the initial trials and also for the athletes during the modality of kinesthetic motor imagery.

Encoding of speed and direction of movement in the human supplementary motor area

OBJECT

The supplementary motor area (SMA) plays an important role in planning, initiation, and execution of motor acts. Patients with SMA lesions are impaired in various kinematic parameters, such as velocity and duration of movement. However, the relationships between neuronal activity and these parameters in the human brain have not been fully characterized. This is a study of single-neuron activity during a continuous volitional motor task, with the goal of clarifying these relationships for SMA neurons and other frontal lobe regions in humans.

METHODS

The participants were 7 patients undergoing evaluation for epilepsy surgery requiring implantation of intracranial depth electrodes. Single-unit recordings were conducted while the patients played a computer game involving movement of a cursor in a simple maze.

RESULTS

In the SMA proper, most of the recorded units exhibited a monotonic relationship between the unit firing rate and hand motion speed. The vast majority of SMA proper units with this property showed an inverse relation, that is, firing rate decrease with speed increase. In addition, most of the SMA proper units were selective to the direction of hand motion. These relationships were far less frequent in the pre-SMA, anterior cingulate gyrus, and orbitofrontal cortex.

CONCLUSIONS

The findings suggest that the SMA proper takes part in the control of kinematic parameters of endeffector motion, and thus lend support to the idea of connecting neuroprosthetic devices to the human SMA.

Single-trial discrimination of type and speed of wrist movements from EEG recordings

OBJECTIVE

The study explored the possibility of identifying movement type and speed from EEG recordings.

METHODS

EEG signals were acquired from 9 healthy volunteers during imagination of four tasks of the right wrist that involved two speeds (fast and slow) and two types of movement (wrist extension and rotation), each repeated 60 times in random order. Average movement-related cortical potentials (MRCPs) were compared among the four tasks. Moreover, single-trial classification was performed using the rebound rate of MRCP and the power in the mu and beta bands as features.

RESULTS

The rebound rate of the average MRCPs was greater for faster than for slower movements but did not depend on the type of movement. Accordingly, pairs of tasks executed at different speeds led to lower misclassification rate than pairs of tasks executed at the same speed. The average misclassification rate between task pairs was 21+/-2% for the best channel and task pair.

CONCLUSION

The task parameter speed can be discriminated in single-trial EEG traces with greater accuracy than the type of movement when tasks are executed at the same joint.

SIGNIFICANCE

The speed of movement execution may be included among the variables that characterize imagined tasks for brain-computer interface applications.

EEG features extraction for motor imagery

Motor imagery is the mental simulation of a motor act that includes preparation for movement, passive observations of action and mental operations of motor representations implicitly or explicitly. Motor imagery as preparation for immediate movement likely involves the motor executive brain regions. Implicit mental operations of motor representations are considered to underlie cognitive functions. Another problem concerning neuro-imaging studies on motor imagery is that the performance of imagination is very difficult to control. The ability of an individual to control its EEG may enable him to communicate without being able to control their voluntary muscles. Communication based on EEG signals does not require neuromuscular control and the individuals who have neuromuscular disorders and who may have no more control over any of their conventional communication abilities may still be able to communicate through a direct brain-computer interface. A brain-computer interface replaces the use of nerves and muscles and the movements they produce with electrophysiological signals and is coupled with the hardware and software that translate those signals into physical actions. One of the most important components of a brain-computer interface is the EEG feature extraction procedure. This paper presents an approach that uses self-organizing fuzzy neural network based time series prediction that performs EEG feature extraction in the time domain only. EEG is recorded from two electrodes placed on the scalp over the motor cortex. EEG signals from each electrode are predicted by a single fuzzy neural network. Features derived from the mean squared error of the predictions and from the mean squared of the predicted signals are extracted from EEG data by means of a sliding window. The architecture of the two auto-organizing fuzzy neural networks is a network with multi inputs and single output.

Visuo-motor learning with combination of different rates of motor imagery and physical practice

Sports psychology suggests that mental rehearsal facilitates physical practice in athletes and clinical rehabilitation attempts to use mental rehearsal to restore motor function in hemiplegic patients. Our aim was to examine whether mental rehearsal is equivalent to physical learning, and to determine the optimal proportions of real execution and rehearsal. Subjects were asked to grasp an object and insert it into an adapted slot. One group (G0) practiced the task only by physical execution (240 trials); three groups imagined performing the task in different rates of trials (25%, G25; 50%, G50; 75%, G75), and physically executed movements for the remaining trials; a fourth, control group imagined a visual rotation task in 75% of the trials and then performed the same motor task as the others groups. Movement time (MT) was compared for the first and last physical trials, together with other key trials, across groups. All groups learned, suggesting that mental rehearsal is equivalent to physical motor learning. More importantly, when subjects rehearsed the task for large numbers of trials (G50 and G75), the MT of the first executed trial was significantly shorter than the first executed trial in the physical group (G0), indicating that mental practice is better than no practice at all. Comparison of the first executed trial in G25, G50 and G75 with the corresponding trials in G0 (61, 121 and 181 trials), showed equivalence between mental and physical practice. At the end of training, the performance was much better with high rates of mental practice (G50/G75) compared to physical practice alone (G0), especially when the task was difficult. These findings confirm that mental rehearsal can be beneficial for motor learning and suggest that imagery might be used to supplement or partly replace physical practice in clinical rehabilitation.

When thoughts become action: an fMRI paradigm to study volitional brain activity in non-communicative brain injured patients

The assessment of voluntary behavior in non-communicative brain injured patients is often challenging due to the existence of profound motor impairment. In the absence of a full understanding of the neural correlates of consciousness, even a normal activation in response to passive sensory stimulation cannot be considered as proof of the presence of awareness in these patients. In contrast, predicted activation in response to the instruction to perform a mental imagery task would provide evidence of voluntary task-dependent brain activity, and hence of consciousness, in non-communicative patients. However, no data yet exist to indicate which imagery instructions would yield reliable single subject activation. The aim of the present study was to establish such a paradigm in healthy volunteers. Two exploratory experiments evaluated the reproducibility of individual brain activation elicited by four distinct mental imagery tasks. The two most robust mental imagery tasks were found to be spatial navigation and motor imagery. In a third experiment, where these two tasks were directly compared, differentiation of each task from one another and from rest periods was assessed blindly using a priori criteria and was correct for every volunteer. The spatial navigation and motor imagery tasks described here permit the identification of volitional brain activation at the single subject level, without a motor response. Volunteer as well as patient data [Owen, A.M., Coleman, M.R., Boly, M., Davis, M.H., Laureys, S., Pickard J.D., 2006. Detecting awareness in the vegetative state. Science 313, 1402] strongly suggest that this paradigm may provide a method for assessing the presence of volitional brain activity, and thus of consciousness, in non-communicative brain-injured patients.

Neural Adaptations to Resistive Exercise

It is generally accepted that neural factors play an important role in muscle strength gains. This article reviews the neural adaptations in strength, with the goal of laying the foundations for practical applications in sports medicine and rehabilitation. An increase in muscular strength without noticeable hypertrophy is the first line of evidence for neural involvement in acquisition of muscular strength. The use of surface electromyographic (SEMG) techniques reveal that strength gains in the early phase of a training regimen are associated with an increase in the amplitude of SEMG activity. This has been interpreted as an increase in neural drive, which denotes the magnitude of efferent neural output from the CNS to active muscle fibres. However, SEMG activity is a global measure of muscle activity. Underlying alterations in SEMG activity are changes in motor unit firing patterns as measured by indwelling (wire or needle) electrodes. Some studies have reported a transient increase in motor unit firing rate. Training-related increases in the rate of tension development have also been linked with an increased probability of doublet firing in individual motor units. A doublet is a very short interspike interval in a motor unit train, and usually occurs at the onset of a muscular contraction. Motor unit synchronisation is another possible mechanism for increases in muscle strength, but has yet to be definitely demonstrated. There are several lines of evidence for central control of training-related adaptation to resistive exercise. Mental practice using imagined contractions has been shown to increase the excitability of the cortical areas involved in movement and motion planning. However, training using imagined contractions is unlikely to be as effective as physical training, and it may be more applicable to rehabilitation. Retention of strength gains after dissipation of physiological effects demonstrates a strong practice effect. Bilateral contractions are associated with lower SEMG and strength compared with unilateral contractions of the same muscle group. SEMG magnitude is lower for eccentric contractions than for concentric contractions. However, resistive training can reverse these trends. The last line of evidence presented involves the notion that unilateral resistive exercise of a specific limb will also result in training effects in the unexercised contralateral limb (cross-transfer or cross-education). Peripheral involvement in training-related strength increases is much more uncertain. Changes in the sensory receptors (i.e. Golgi tendon organs) may lead to disinhibition and an increased expression of muscular force. Agonist muscle activity results in limb movement in the desired direction, while antagonist activity opposes that motion. Both decreases and increases in co-activation of the antagonist have been demonstrated. A reduction in antagonist co-activation would allow increased expression of agonist muscle force, while an increase in antagonist co-activation is important for maintaining the integrity of the joint. Thus far, it is not clear what the CNS will optimise: force production or joint integrity. The following recommendations are made by the authors based on the existing literature. Motor learning theory and imagined contractions should be incorporated into strength-training practice. Static contractions at greater muscle lengths will transfer across more joint angles. Submaximal eccentric contractions should be used when there are issues of muscle pain, detraining or limb immobilisation. The reversal of antagonists (antagonist-to-agonist) proprioceptive neuromuscular facilitation contraction pattern would be useful to increase the rate of tension development in older adults, thus serving as an important prophylactic in preventing falls. When evaluating the neural changes induced by strength training using EMG recording, antagonist EMG activity should always be measured and evaluated.

Movement-related parameters modulate cortical activity during imaginary isometric plantar-flexions

A multitude of studies have demonstrated a clear activation of the motor cortex during imagination of various motor tasks; however, it is still unclear if movement-related parameters (movement direction, range of motion, speed, force level and rate of force development) specifically modulate cortical activation as they do during the execution of actual motor tasks. Accordingly, this study examined whether the rate of torque development (RTD) and/or the torque amplitude modulates cortical potentials generated during imaginary motor tasks. Fifteen subjects imagined four different left-sided isometric plantar-flexion tasks, while EEG and EMG recordings were being performed. The averaged EEG activity was analyzed in terms of movement-related potentials (MRPs), consisting of readiness potential (RP), motor potential (MP) and movement-monitoring potential (MMP). It was demonstrated that RTD and torque amplitude indeed modulate cortical activity during imaginary motor tasks. Information concerning movement-related parameters for imaginary plantar-flexion tasks seems to be encoded in the supplementary motor area (SMA) and the primary motor cortex (M1). A comparison between MRPs of imaginary and actual motor tasks revealed that early MRPs were morphologically similar, but differed significantly in amplitude. One of the possible suggestions to explain such a difference may be an "abortion" of ongoing motor programs.

EMG Activity in Selected Target Muscles During Imagery Rising on Tiptoes in Healthy Adults and Poststrokes Hemiparetic Patients

The authors sought to gain further knowledge about activation of target muscles during imagery engagement in a motor task. Six hemiparetic patients and 9 healthy participants performed 3 real rises on tiptoes and then, after pausing, 3 imagery rises on tiptoes. Metronome beats guided the rate of rises and descents. Electromyographic (EMG) activity from the medial gastrocnemius and the rectus femoris muscles were monitored bilaterally throughout the performance of both tasks. In 3 healthy participants and 3 individuals with hemiparesis, EMG activity was related to the imagery task in at least 1 of the target muscles. Conversely, in the other participants, motor imagery practice was not accompanied by task-related EMG activity in the monitored muscles. In all cases, the increment in activation level during motor imagery practice was very low in comparison with that of real performance. The findings were not unequivocal; therefore, EMG activity may sometimes, but not always, be recorded during motor imagery practice both in healthy individuals and in poststroke hemiparetic participants. Further research is needed to align motor imagery practice with the objectives of motor rehabilitation.

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.

Hand effects on mentally simulated reaching

Within the area of simulated (imagined) versus actual movement research, investigators have discovered that mentally simulated movements, like real actions, are controlled primarily by the hemispheres contralateral to the simulated limb. Furthermore, evidence points to a left-brain advantage for accuracy of simulated movements. With this information it could be suggested that, compared to left-handers, most right-handers would have an advantage. To test this hypothesis, strong right- and left-handers were compared on judgments of perceived reachability to visual targets lasting 150 ms in multiple locations of midline, right- and left-visual field (RVF/LVF). In reference to within group responses, we found no hemispheric or hand use advantage for right-handers. Although left-handers revealed no hemispheric advantage, there was a significant hand effect, favoring the non-dominant limb, most notably in LVF. This finding is explained in regard to a possible interference effect for left-handers, not shown for right-handers. Overall, left-handers displayed significantly more errors across hemispace. Therefore, it appears that when comparing hand groups, a left-hemisphere advantage favoring right-handers is plausible.

Motor imagery in reaching: is there a left-hemispheric advantage?

The study of motor imagery affords an attractive approach in the quest to identify the specific aspects of cognitive and neuromotor mechanisms and relationship involved in action processing. Here, the authors investigated the recently reported finding that compared to the left-hemisphere, the right brain is at a significant disadvantage for mentally simulating reaching movements. The authors investigated this observation with strong right-handers that were asked to estimate the imagined reachability of visual targets (presented at 150 ms) at multiple points at midline, right- and left visual field; responses were compared to actual maximum reaching distance. Results indicated that individuals are relatively accurate at imagined reachability, with no significant distinction between visual field responses. Therefore, these data provide no evidence to support the claim that the right hemisphere is significantly inferior to the left hemisphere in estimations of motor imagery for reaching. The authors do acknowledge differences in the experimental task and subject characteristics compared to earlier work using split-brain and stroke patients.

Kraftgewinne durch Vorstellung maximaler Muskelkontraktionen

Zusammenfassung. In der vorliegenden Trainingsstudie wurde der Effekt imaginierter Muskelkontraktionen (IMC-Training) auf die isometrische Maximalkraft (MVC) untersucht. In der Literatur finden sich hierzu teils widersprüchliche Befunde ( Herbert, Dean & Gandevia, 1998 ; Yue & Cole, 1992 . Im Rahmen eines vierwöchigen kontrollierten Trainingsprogramms trainierten Versuchspersonen (N = 34) die Kraftübung Bankdrücken entweder physisch (Gruppe “MaxKraft“, n = 12), d. h. mit maximalen isometrischen Kontraktionen oder indem sie die entsprechenden Kontraktionen so lebhaft als möglich imaginierten (Gruppe “Mental“, n = 11). Die Kontrollgruppe (n = 11) hatte kein Training. Vor, während (nach 7 bzw. 14 Tagen) und am Ende der Trainingsphase wurde die Relativkraft (MVC relativiert am Körpergewicht) erfasst. Im Gegensatz zur Kontrollgruppe verzeichnet die mental übende Gruppe einen signifikanten Kraftgewinn (5.7 %; p < .001). Der stärkste Vorstellungseffekt findet sich dabei zu Beginn der Trainingsphase (η2 = .58). Der Kraftanstieg in Folge eines IMC-Trainings wird als Verbesserung der muskulären Aktivierung und somit als Anpassung der zentralen Programmierung interpretiert. Die Kraftgewinne der physisch übenden Gruppe (14.1 %) werden allerdings nicht erreicht.

Perceived reachability in hemispace

A common observation in studies of perceived (imagined) compared to actual movement in a reaching paradigm is the tendency to overestimate. Of the studies noted, reaching tasks have been presented in the general midline range. In the present study, strong right-handers were asked to judge the reachability of visual targets projected onto a table surface at midline, right- (RVF), and left-visual fields (LVF). Midline results support those of previous studies, showing an overestimation bias. In contrast, participants revealed the tendency to underestimate their reachability in RVF and LVF. These findings are discussed from the perspective of actor 'confidence' (a cognitive state) possibly associated with visual information, perceived ability, and perceived task demands.

Is the human primary motor cortex involved in motor imagery?

Participation of the primary motor cortex (M1) in motor imagery was addressed using functional magnetic resonance imaging at 2.0 T and 2 x 2 x 4 mm3 resolution in six right-handed subjects. Paradigms comprised visually cued execution and imagination of a sequential finger-to-thumb opposition task (12 s) contrasted with motor rest and visual imagery (18 s), respectively. Motor execution activated M1 as well as other parts of the motor system including supplementary motor area (SMA) and premotor areas (PM). In contrast, motor imagery did not lead to activations in M1 except for 1/6 subjects but involved SMA and PM bilaterally as well as the anterior intraparietal cortex. Moreover, a region-of-interest analysis revealed a weak initial MRI signal increase in M1 in 4/6 subjects. This novel finding of a transient response reflecting the onset of imagination which does not lead to sustained M1 activation may explain previous contradictory reports.

Single-neuron activity in the human supplementary motor area underlying preparation for action

OBJECT

The supplementary motor area (SMA) is considered critical in the planning, initiation, and execution of motor acts. Despite decades of research, including electrical stimulation mapping in patients undergoing neurosurgery, the contribution of this region to the generation of motor behavior has remained enigmatic. This is a study of single-neuron responses at various stages of a motor task during depth electrode recording in the SMA, pre-SMA, and medial temporal lobe of humans, with the goal of elucidating the disparate roles of neurons in these regions during movements.

METHODS

The patients were undergoing evaluation for epilepsy surgery requiring implantation of intracranial depth electrodes. Single-unit recordings were made during both the execution and mental imagery of finger apposition sequences. Only medial frontal neurons responded selectively to specific features of the motor plan, such as which hand performed the motor activity or the complexity of the sequence. Neuron activity progressively increased before the patient was given a "go" cue for the execution of movements; this activity peaked earlier in the pre-SMA than in the SMA proper. We observed similar patterns of activation during motor imagery and actual movement, but only neurons in the SMA differentiated between imagined and real movements.

CONCLUSIONS

These results provide support at the single-neuron level for the role of the medial frontal cortex in the temporal organization and planning of movements in humans.

What drives children's limb selection for reaching in hemispace?

Arguably, the act of reaching constitutes one of the most devoted lines of contemporary developmental research. In addition to the underlying dynamical characteristics of motor coordination, a key element in programming is limb selection, a phenomenon (handedness) that has so far resisted any reasonable unified explanation. From a more contemporary view, two factors appear to have the most influence on hand selection for a given task: motor dominance and attentional information related to task demands. This study was designed to determine what factor(s) influence choice of limb for reaching in hemispace in reference to motor dominance, object proximity, and a hemispheric bias favoring use of the hand on the same side as the stimulus. Strong right-handed children were asked to reach and retrieve a small object across right and left hemispace locations beginning with the arms uncrossed and arms-crossed. With the arms-crossed condition, an imagined and actual movement execution was administered. Results from the uncrossed condition supported previous reported findings for adults and children. That is, participants responded ipsilaterally using the hand on the same side as the stimulus, thus supporting the case for object proximity and hemispheric bias. However, in the arms-crossed condition the vast majority of participants preferred keeping the limbs crossed in response to right and left hemispace stimuli, which leads to the suggestion that object proximity rather than hemispheric bias was the driving factor in this context. The behavioral pattern for imagined and actual movement was not significantly different. Overall, the findings add to the growing acceptance that limb selection is task and context dependent, rather than a biologically based invariant feature of motor behavior.

Sensation of effort is altered in Huntington's disease

In this study, we investigated sensation of effort in Huntington disease (HD). We tested the hypothesis that the basal ganglia are involved in processing effort sensation. The experimental paradigm consisted in a contralateral matching procedure where normal subjects (N=6) and HD patients (N=6) were required to lift a reference weight with their non-dominant index, and then compare the target-weight with variable weights lifted by the dominant index. Two kinds of sequences were administered: (1) increasing, where the first weight was lighter than the reference weight and progressively increased in 20g steps, (2) decreasing, where trials started with a heavier weight and progressively decreased. We calculated the discrimination threshold (DT) across sequences as the weight for which the subject's response changed sign. The difference between the higher and the lower threshold was defined as "uncertain area". We predicted that controls should overestimate the reference weight lifted by their non-dominant hand because the same effort produces more force when applied to stronger muscles. If the basal ganglia mediates sensation of effort, patients' capability to discriminate weights should be degraded. As expected, normal subjects overestimated the reference weight lifted by their non-dominant index and showed a restricted uncertain area, thus, indicating that were able to discriminate minimal differences in generated forces. By contrast, patients with HD underestimated the reference weight lifted by their non-dominant hand and showed a broad uncertain area, thus, demonstrating that they could detect only important differences in the matched efforts. These results suggest that effort sensation critically involves the basal ganglia. In normal conditions, in parallel with the efferent command of force, an efferent copy reflecting the magnitude of the voluntary motor command is transmitted to sensory centres. This signal and/or the integration of sensory feedback which generates what is experienced as the sense of effort, would be altered in HD.