Movement related potentials in acutely induced weakness and stroke

The Effect of Virtual Reality on Motor Anticipation and Hand Function in Patients with Subacute Stroke: A Randomized Trial on Movement-Related Potential

Background

Impaired cognitive ability to anticipate the required control for an upcoming task in patients with stroke may affect rehabilitation outcome. The cortical excitability of task-related motor anticipation for upper limb movement induced by virtual reality (VR) training remains unclear.

Aims

To investigate the effect of VR training on the cortical excitability of motor anticipation when executing upper limb movement in patients with subacute stroke.

Methods

A total of thirty-six stroke survivors with upper limb hemiparesis resulting from the first occurrence of stroke within 1 to 3 months were recruited. Participants were randomly allocated to the VR intervention group or conventional therapy group. Event-related potentials (ERPs) and electromyography (EMG) were used to simultaneously record the cortical excitability and muscle activities during palmar grasp motion. Outcome measures of the contingent negative variation (CNV) latency and amplitude, EMG reaction time, Upper Limb Fugl-Meyer Assessment (UL-FMA), Action Research Arm Test (ARAT), and National Institutes of Health Stroke Scale (NIHSS) were recorded pre- and postintervention. The between-group difference was analysed by mixed model ANOVA.

Results

The EMG onset time of the paretic hand in the VR group was earlier than that observed in the control group (t = 2.174, p = 0.039) postintervention. CNV latency reduction postintervention was larger in the VR group than in the control group (t = 2.411, p = 0.021) during paretic hand movement. The reduction in CNV amplitude in the VR group was larger in the VR group than in the control group (p < 0.001 for all electrodes except for C3) when executing paretic hand movement. ARAT and UL-FMA scores were significantly higher in the VR group than in the control group (p = 0.019 and p = 0.037, respectively) postintervention. No significant difference in the reduction in NIHSS was found between the VR and control groups (p = 0.072).

Conclusions

VR intervention is superior to conventional therapy to improve the cognitive neural process of motor anticipation and reduce the excessive compensatory activation of the contralesional hemisphere. The improvements observed in the cognitive neural process corroborated with the improvements in hand function.

Neuroplasticity of Cortical Planning for Initiating Stepping Poststroke: A Case Series

BACKGROUND AND PURPOSE

Therapeutic exercise improves balance and walking ability in individuals after stroke. The extent to which motor planning improves with therapeutic exercise is unknown. This case series examined how outpatient physical therapy affects motor planning and motor performance for stepping.

CASE DESCRIPTION

Individuals poststroke performed self-initiated stepping before (baseline), after (postintervention), and 1 month after (retention) intervention. Amplitude and duration of the movement-related cortical potential (MRCP) was measured using an electroencephalograph from the Cz electrode. Electromyography (EMG) of biceps femoris (BF) was collected. Additionally, clinical measures of motor impairment and function were evaluated at all 3 time points by a blinded assessor.

INTERVENTION

Two types of outpatient physical therapy were performed for 6 weeks: CONVENTIONAL (n = 3) and FAST (n = 4, Fast muscle Activation and Stepping Training).

OUTCOMES

All 7 participants reduced MRCP duration, irrespective of the type of physical therapy. The MRCP amplitude and BF EMG onset changes were more variable. Clinical outcomes improved or were maintained for all participants. The extent of motor impairment was associated with MRCP amplitude.

DISCUSSION

Changes in MRCP duration suggest that outpatient physical therapy may promote neuroplasticity of motor planning of stepping movements after stroke; however, a larger sample is needed to determine whether this finding is valid.This case series suggests motor planning for initiating stepping may improve after 6 weeks of outpatient physical therapy for persons with stroke.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A307).

Assessing the Relationship Between Motor Anticipation and Cortical Excitability in Subacute Stroke Patients With Movement-Related Potentials

Background: Stroke survivors may lack the cognitive ability to anticipate the required control for palmar grasp execution. The cortical mechanisms involved in motor anticipation of palmar grasp movement and its association with post-stroke hand function remains unknown. Aims: To investigate the cognitive anticipation process during a palmar grasp task in subacute stroke survivors and to compare with healthy individuals. The association between cortical excitability and hand function was also explored. Methods: Twenty-five participants with hemiparesis within 1-6 months after first unilateral stroke were recruited. Twenty-five matched healthy individuals were recruited as control. Contingent negative variation (CNV) was measured using electroencephalography recordings (EEG). Event related potentials were elicited by cue triggered hand movement paradigm. CNV onset time and amplitude between pre-cue and before movement execution were recorded. Results: The differences in CNV onset time and peak amplitude were statistically significant between the subacute stroke and control groups, with patients showing earlier onset time with increased amplitudes. However, there was no statistically significant difference in CNV onset time and peak amplitude between lesioned and non-lesioned hemisphere in the subacute stroke group. Low to moderate linear associations were observed between cortical excitability and hand function. Conclusions: The earlier CNV onset time and higher peak amplitude observed in the subacute stroke group suggest increased brain computational demand during palmar grasp task. The lack of difference in CNV amplitude between the lesioned and non-lesioned hemisphere within the subacute stroke group may suggest that the non-lesioned hemisphere plays a role in the motor anticipatory process. The moderate correlations suggested that hand function may be associated with cortical processing of motor anticipation.

Combining Movement-Related Cortical Potentials and Event-Related Desynchronization to Study Movement Preparation and Execution

This study applied a comprehensive electroencephalography (EEG) analysis for movement-related cortical potentials (MRCPs) and event-related desynchronization (ERD) in order to understand movement-related brain activity changes during movement preparation and execution stage of unilateral wrist extension. Thirty-four healthy subjects completed two event-related potential tests in the same sequence. Unilateral wrist extension was involved in both tests as the movement task. Instruction Response Movement (IRM) was a brisk movement response task with visual “go” signal, while Cued Instruction Response Movement (CIRM) added a visual cue contenting the direction information to create a prolonged motor preparation stage. Recorded EEG data were segmented and averaged to show time domain changes and then transformed into time-frequency mapping to show the time-frequency changes. All components were calculated and compared among C3, Cz, and C4 locations. The motor potential appeared bilaterally in both tests' movement execution stages, and Cz had the largest peak value among the investigated locations (p < 0.01). In CIRM, a contingent negative variation (CNV) component presented bilaterally during the movement preparation stage with the largest amplitude at Cz. ERD of the mu rhythm (mu ERD) presented bilateral sensorimotor cortices during movement execution stages in both tests and was the smallest at Cz among the investigated locations. In the movement preparation stage of CIRM, mu ERD presented mainly in the contralateral sensory motor cortex area (C3 and C4 for right and left wrist movements, respectively) and showed significant differences between different locations. EEG changes in the time and time-frequency domains showed different topographical features. Movement execution was controlled bilaterally, while movement preparation was controlled mainly by contralateral sensorimotor cortices. Mu ERD was found to have stronger contra-lateralization features in the movement preparation stage and might be a better indicator for detecting movement intentions. This information could be helpful and might provide comprehensive information for studying movement disorders (such as those in post-stroke hemiplegic patients) or for facilitating the development of neuro-rehabilitation engineering technology such as brain computer interface.

A Ternary Brain-Computer Interface Based on Single-Trial Readiness Potentials of Self-initiated Fine Movements: A Diversified Classification Scheme

In recent years, the readiness potential (RP), a type of pre-movement neural activity, has been investigated for asynchronous electroencephalogram (EEG)-based brain-computer interfaces (BCIs). Since the RP is attenuated for involuntary movements, a BCI driven by RP alone could facilitate intentional control amid a plethora of unintentional movements. Previous studies have mainly attempted binary single-trial classification of RP. An RP-based BCI with three or more states would expand the options for functional control. Here, we propose a ternary BCI based on single-trial RPs. This BCI classifies amongst an idle state, a left hand and a right hand self-initiated fine movement. A pipeline of spatio-temporal filtering with per participant parameter optimization was used for feature extraction. The ternary classification was decomposed into binary classifications using a decision-directed acyclic graph (DDAG). For each class pair in the DDAG structure, an ordered diversified classifier system (ODCS-DDAG) was used to select the best among various classification algorithms or to combine the results of different classification algorithms. Using EEG data from 14 participants performing self-initiated left or right key presses, punctuated with rest periods, we compared the performance of ODCS-DDAG to a ternary classifier and four popular multiclass decomposition methods using only a single classification algorithm. ODCS-DDAG had the highest performance (0.769 Cohen's Kappa score) and was significantly better than the ternary classifier and two of the four multiclass decomposition methods. Our work supports further study of RP-based BCI for intuitive asynchronous environmental control or augmentative communication.

Change in Movement-Related Cortical Potentials Following Constraint-Induced Movement Therapy (CIMT) After Stroke

Abstract. Patients with chronic stroke were given Constraint-Induced Movement Therapy (CIMT) over an intensive two-week course of treatment. The intervention resulted in a large improvement in use of the more-affected upper extremity in the laboratory and in the real-world environment. High-resolution electroencephalography (EEG) showed that the treatment produced marked changes in cortical activity that correlated with the significant rehabilitative effects. Repetitive unilateral self-paced voluntary movements showed a large increase after treatment in the amplitudes of the late components of the Bereitschaftspotential (BP) both in the hemisphere contralateral to the more-affected arm and in the ipsilateral hemisphere. Simultaneous electromyographic recordings (EMG) and other aspects of the data indicate that the emergence of the movement-related neural source in the healthy hemisphere was not due to mirror movements of the non-test hand and that the increase in BP amplitudes was not the result of an increase in the force or effort of the response pre- to post-treatment. The results are consistent with the rehabilitation treatment having produced a use-dependent cortical reorganization and is a case where the physiological data interdigitates with and provides additional credibility to the clinical data.

Movement related cortical potentials in severe chronic stroke

Movement related cortical potentials (MRCPs) have been studied for many years and controlled using brain computer interfaces (BCIs). Furthermore, MRCPs have been proposed as reliable and immediate indicators of cortical reorganizations in motor learning and after stroke. In this study MRCPs preceding and during hand movements in severe chronic stroke were investigated. Eight severely impaired (no residual finger extension) chronic stoke patients underwent EEG and EMG recordings during a cue triggered hand movement paradigm. Four patients presented subcortical lesions only while the other four presented mixed (cortical and subcortical) lesions. MRCPs were measured before (slow cortical potentials SCPs) and at movement onset (motor potentials MPs). SCPs were observed during paretic hand movements only. Latencies were longer and reached their negativity peak earlier during paretic hand movement. When dividing the patients in subcortical only and mixed lesion patients, we observed significantly bigger MP peak amplitudes over the lesioned hemisphere during paretic and healthy hand movements in subcortical stroke patients. Furthermore, we observed a significant difference in MP peak latency between subcortical and mixed stroke patients during paretic hand movements. We demonstrated for the first time significant differences between subcortical only and mixed (cortical and subcortical) stroke patients' MRCPs during motor preparation and execution. Furthermore, we demonstrated how stroke produces a longer MRCP and that lesion location affects MP peak amplitude and latency. Finally, we propose the use MRCP based BCIs to reduce their duration (towards normal) and induce motor function recovery.

Movement related slow cortical potentials in severely paralyzed chronic stroke patients

Movement-related slow cortical potentials (SCPs) are proposed as reliable and immediate indicators of cortical reorganization in motor learning. SCP amplitude and latency have been reported as markers for the brain's computational effort, attention and movement planning. SCPs have been used as an EEG signature of motor control and as a main feature in Brain-Machine-Interfaces (BMIs). Some reports suggest SCPs are modified following stroke. In this study, we investigated movement-related SCPs in severe chronic stroke patients with no residual paretic hand movements preceding and during paretic (when they try to move) and healthy hand movements. The aim was to identify SCP signatures related to cortex integrity and complete paralysis due to stroke in the chronic stage. Twenty severely impaired (no residual finger extension) chronic stoke patients, of whom ten presented subcortical and ten cortical and subcortical lesions, underwent EEG and EMG recordings during a cue triggered hand movement (open/close) paradigm. SCP onset appeared and peaked significantly earlier during paretic hand movements than during healthy hand movements. Amplitudes were significantly larger over the midline (Cz, Fz) for paretic hand movements while contralateral (C4, F4) and midline (Cz, Fz) amplitudes were significantly larger than ipsilateral activity for healthy hand movements. Dividing the participants into subcortical only and mixed lesioned patient groups, no significant differences observed in SCP amplitude and latency between groups. This suggests lesions in the thalamocortical loop as the main factor in SCP changes after stroke. Furthermore, we demonstrated how, after long-term complete paralysis, post-stroke intention to move a paralyzed hand resulted in longer and larger SCPs originating in the frontal areas. These results suggest SCP are a valuable feature that should be incorporated in the design of new neurofeedback strategies for motor neurorehabilitation.

Movement-related cortical potentials during muscle fatigue induced by upper limb submaximal isometric contractions

The aim of this study was to examine the central neurophysiological mechanisms during fatigue induced by submaximal isometric contractions. A total of 23 individuals participated in the study and were assigned to fatigue and nonfatigue groups. Handgrip force, root mean square (RMS) of surface electromyography (sEMG) signal and movement-related cortical potentials during self-paced submaximal handgrip isometric contractions were assessed for each participant. The experimental data showed significant decreases in both maximal voluntary contraction [-24.3%; F(3, 42)=19.62, P<0.001, ηp=0.48] and RMS [-30.1%; F(3, 42)=19.01, P<0.001, ηp=0.57] during maximal voluntary contractions and a significant increase [F(3, 42)=14.27, P<0.001, ηp=0.50] in the average RMS of sEMG over four blocks in the fatigue group. There was no significant difference in the readiness potential between the fatigue and the nonfatigue groups at early stages, and at late stages, significant differences were observed only at the Fp1 and FC1 sites. Motor potential amplitudes were significantly higher in the fatigue group than in the nonfatigue group irrespective of block or electrode positions. Positive waveforms were observed in the prefrontal cortex in states without muscle fatigue, whereas a negative waveform pattern was observed with muscle fatigue. Significant within-subject correlations were observed between motor potential at the C1 site and RMS of sEMG (r=-0.439, P=0.02, ηp=0.11). Neurophysiological evidence indicates that cortical activity increases in the prefrontal cortex, primary motor cortex and supplementary motor cortex with muscle fatigue. Muscle fatigue appears to have considerable effects on the components of movement-related cortical potentials during movement execution, whereas the readiness potential before movement is sensitive to cognitive demands during prolonged exercise. Our results provide additional evidence for a link between central motor command during movement execution and motor unit recruitment.

Spatiotemporal dynamics of online motor correction processing revealed by high-density electroencephalography

The ability to control online motor corrections is key to dealing with unexpected changes arising in the environment with which we interact. How the CNS controls online motor corrections is poorly understood, but evidence has accumulated in favor of a submovement-based model in which apparently continuous movement is segmented into distinct submovements. Although most studies have focused on submovements' kinematic features, direct links with the underlying neural dynamics have not been extensively explored. This study sought to identify an electroencephalographic signature of submovements. We elicited kinematic submovements using a double-step displacement paradigm. Participants moved their wrist toward a target whose direction could shift mid-movement with a 50% probability. Movement kinematics and cortical activity were concurrently recorded with a low-friction robotic device and high-density electroencephalography. Analysis of spatiotemporal dynamics of brain activation and its correlation with movement kinematics showed that the production of each kinematic submovement was accompanied by (1) stereotyped topographic scalp maps and (2) frontoparietal ERPs time-locked to submovements. Positive ERP peaks from frontocentral areas contralateral to the moving wrist preceded kinematic submovement peaks by 220-250 msec and were followed by positive ERP peaks from contralateral parietal areas (140-250 msec latency, 0-80 msec before submovement peaks). Moreover, individual subject variability in the latency of frontoparietal ERP components following the target shift significantly predicted variability in the latency of the corrective submovement. Our results are in concordance with evidence for the intermittent nature of continuous movement and elucidate the timing and role of frontoparietal activations in the generation and control of corrective submovements.

Detection and classification of movement-related cortical potentials associated with task force and speed

OBJECTIVE

In this study, the objective was to detect movement intentions and extract different levels of force and speed of the intended movement from scalp electroencephalography (EEG). We then estimated the performance of the closed loop system.

APPROACH

Cued movements were detected from continuous EEG recordings using a template of the initial phase of the movement-related cortical potential in 12 healthy subjects. The temporal features, extracted from the movement intention, were classified with an optimized support vector machine. The system performance was evaluated when combining detection with classification.

MAIN RESULTS

The system detected 81% of the movements and correctly classified 75 ± 9% and 80 ± 10% of these at the point of detection when varying the force and speed, respectively. When the detector was combined with the classifier, the system detected and correctly classified 64 ± 13% and 67 ± 13% of these movements. The system detected and incorrectly classified 21 ± 7% and 16 ± 9% of the movements. The movements were detected 317 ± 73 ms before the movement onset.

SIGNIFICANCE

The results indicate that it is possible to detect movement intentions with limited latencies, and extract and classify different levels of force and speed, which may be combined with assistive technologies for patient-driven neurorehabilitation.

Motor planning in chronic upper-limb hemiparesis: evidence from movement-related potentials

Background

Chronic hemiplegia is a common long-term consequence of stroke, and subsequent motor recovery is often incomplete. Neurophysiological studies have focused on motor execution deficits in relatively high functioning patients. Much less is known about the influence exerted by processes related to motor preparation, particularly in patients with poor motor recovery.

Methodology/Principal Findings

The current study investigates motor preparation using a modified response-priming experiment in a large sample of patients (n = 50) with moderate-to-severe chronic hemiparesis. The behavioural results revealed that hemiparetic patients had an increased response-priming effect compared to controls, but that their response times were markedly slower for both hands. Patients also demonstrated significantly enhanced midline late contingent negative variation (CNV) during paretic hand preparation, despite the absence of overall group differences when compared to controls. Furthermore, increased amplitude of the midline CNV correlated with a greater response-priming effect. We propose that these changes might reflect greater anticipated effort to respond in patients, and consequently that advance cueing of motor responses may be of benefit in these individuals. We further observed significantly reduced CNV amplitudes over the lesioned hemisphere in hemiparetic patients compared to controls during non-paretic hand preparation, preparation of both hands and no hand preparation. Two potential explanations for these CNV reductions are discussed: alterations in anticipatory attention or state changes in motor processing, for example an imbalance in inter-hemispheric inhibition.

Conclusions/Significance

Overall, this study provides evidence that movement preparation could play a crucial role in hemiparetic motor deficits, and that advance motor cueing may be of benefit in future therapeutic interventions. In addition, it demonstrates the importance of monitoring both the non-paretic and paretic hand after stroke and during therapeutic intervention.

Detection of self-paced reaching movement intention from EEG signals

Future neuroprosthetic devices, in particular upper limb, will require decoding and executing not only the user's intended movement type, but also when the user intends to execute the movement. This work investigates the potential use of brain signals recorded non-invasively for detecting the time before a self-paced reaching movement is initiated which could contribute to the design of practical upper limb neuroprosthetics. In particular, we show the detection of self-paced reaching movement intention in single trials using the readiness potential, an electroencephalography (EEG) slow cortical potential (SCP) computed in a narrow frequency range (0.1–1 Hz). Our experiments with 12 human volunteers, two of them stroke subjects, yield high detection rates prior to the movement onset and low detection rates during the non-movement intention period. With the proposed approach, movement intention was detected around 500 ms before actual onset, which clearly matches previous literature on readiness potentials. Interestingly, the result obtained with one of the stroke subjects is coherent with those achieved in healthy subjects, with single-trial performance of up to 92% for the paretic arm. These results suggest that, apart from contributing to our understanding of voluntary motor control for designing more advanced neuroprostheses, our work could also have a direct impact on advancing robot-assisted neurorehabilitation.

Precise temporal association between cortical potentials evoked by motor imagination and afference induces cortical plasticity

In monkeys, the repeated activation of somatosensory afferents projecting onto the motor cortex (M1) has a pivotal role in motor skill learning. Here we investigate if sensory feedback that is artificially generated at specific times during imagination of a dorsiflexion task leads to reorganization of the human M1. The common peroneal nerve was stimulated to generate an afferent volley timed to arrive during specific phases of the cortical potential generated when a movement was imagined (50 repetitions). The change in the output of M1 was quantified by applying single transcranial magnetic stimuli to the area of M1 controlling the tibialis anterior muscle. The results demonstrated that the concomitance between the cognitive process of movement (motor imagination) and the ascending volley due to the peripheral nerve stimulation can lead to significant increases in cortical excitability. These increases were critically dependent on the timing between the peripherally generated afferent volley and the cortical potential generated during the imagined movement. Only if the afferent volley arrived during the peak negative deflection of the potential, were significant alterations in motor cortical output attained. These results demonstrate that an artificially generated signal (the peripheral afferent volley) can interact with a physiologically generated signal in humans leading to plastic changes within the M1, the final output stage for movement generation within the human brain. The results presented may have implications in systems for artificially inducing cortical plasticity in patients with motor impairments (neuromodulation).

Bereitschaftspotential and movement-related potentials: Origin, significance, and application in disorders of human movement

The existence of a slow negative wave, the Bereitschaftspotential ("BP"), preceding voluntary movement by 1 second or more was first reported more than 40 years ago. There appears to be considerable interindividual differences, but there is general agreement that the initial negativity actually consists of two distinct phases. Uncertainty remains about many other properties and features of the response, including nomenclature, which makes the existing literature difficult to synthesize. The duration of the premovement negativity raises questions about how and when voluntary movement is initiated. Premovement negativities can also be seen before (predictably) externally paced movement, and these have similarities to the BP. Although lateralized generators exist, it is likely that the majority of the early component of the BP (BP1 or early BP), arises from the anterior supplementary motor area (SMA) and more rostral pre-SMA. The late phase of the BP (BP2 or late BP) is probably generated by activity in both the SMA proper and the contralateral motor cortex. Changes in the BP occur in several movement disorders, notably Parkinson's disease, in which the pattern is consistent with a failure of pre-SMA activation. The presence (or absence) of a clear preceding negativity can also have diagnostic importance for certain movement disorders.