Equivalent is not equal: Primary motor cortex (MI) activation during motor imagery and execution of sequential movements

The Effect of Motor Imagery Practice on an Aiming Task with Attentional Focus Cues

When one directs their attention to an intended effect (external focus of attention, EFOA), motor performance is generally better than when one directs their attention to their own body movements (internal focus of attention, IFOA). However, the effect of attentional focus is unclear when a skill is practiced through motor imagery (MI) in the absence of physical trials. Participants (N = 30, M = 22.33 yrs, SD = 2.69) in the present study completed three physical trials of a reciprocal aiming task before and (24-h) after MI practice. During MI practice, the EFOA (n = 15) and IFOA (n = 15) groups mentally practiced the task with no physical practice with EFOA-MI or IFOA-MI, respectively, for three consecutive days. Our results showed that both groups significantly improved in accuracy (F1,28 = 6.49, p = .017), supporting the benefit of MI in motor skill acquisition. However, a significant effect of attentional focus was not observed (F1.,28 = 0.445, p = 0.51). We discussed two potential explanations: EFOA/IFOA requires physical trials to affect performance, or individuals must use both EFOA and IFOA in the process of creating imagery of the environment and movements, which may obscure the effect of EFOA and IFOA.

The effects of music combined to paired associative stimulation on motor-evoked potentials and alertness in spinal cord injury patients and healthy subjects

Paired associative stimulation (PAS) consisting of high-intensity transcranial magnetic stimulation (TMS) and high-frequency peripheral nerve stimulation (known as high-PAS) induces plastic changes and improves motor performance in patients with incomplete spinal cord injury (SCI). Listening to music during PAS may potentially improve mood and arousal and facilitate PAS-induced neuroplasticity via auditory-motor coupling, but the effects have not been explored. This pilot study aimed to determine if the effect of high-PAS on motor-evoked potentials (MEPs) and subjective alertness can be augmented with music. Ten healthy subjects and nine SCI patients received three high-PAS sessions in randomized order (PAS only, PAS with music synchronized to TMS, PAS with self-selected music). MEPs were measured before (PRE), after (POST), 30 min (POST30), and 60 min (POST60) after stimulation. Alertness was evaluated with a questionnaire. In healthy subjects, MEPs increased at POST in all sessions and remained higher at POST60 in PAS with synchronized music compared with the other sessions. There was no difference in alertness. In SCI patients, MEPs increased at POST and POST30 in PAS only but not in other sessions, whereas alertness was higher in PAS with self-selected music. More research is needed to determine the potential clinical effects of using music during high-PAS.

Motor cortex activation during visuomotor transformations: evoked potentials during overt and imagined movements

Despite the prevalence of visuomotor transformations in our motor skills, their mechanisms remain incompletely understood, especially when imagery actions are considered such as mentally picking up a cup or pressing a button. Here, we used a stimulus-response task to directly compare the visuomotor transformation underlying overt and imagined button presses. Electroencephalographic activity was recorded while participants responded to highlights of the target button while ignoring the second, non-target button. Movement-related potentials (MRPs) and event-related desynchronization occurred for both overt movements and motor imagery (MI), with responses present even for non-target stimuli. Consistent with the activity accumulation model where visual stimuli are evaluated and transformed into the eventual motor response, the timing of MRPs matched the response time on individual trials. Activity-accumulation patterns were observed for MI, as well. Yet, unlike overt movements, MI-related MRPs were not lateralized, which appears to be a neural marker for the distinction between generating a mental image and transforming it into an overt action. Top-down response strategies governing this hemispheric specificity should be accounted for in future research on MI, including basic studies and medical practice.

A comprehensive guide to BCI-based stroke neurorehabilitation interventions

Brain-Computer Interfaces (BCIs) offer the potential to facilitate neurorehabilitation in stroke patients by decoding user intentions from the central nervous system, thereby enabling control over external devices. Despite their promise, the diverse range of intervention parameters and technical challenges in clinical settings have hindered the accumulation of substantial evidence supporting the efficacy and effectiveness of BCIs in stroke rehabilitation. This article introduces a practical guide designed to navigate through these challenges in conducting BCI interventions for stroke rehabilitation. Applicable regardless of infrastructure and study design limitations, this guide acts as a comprehensive reference for executing BCI-based stroke interventions. Furthermore, it encapsulates insights gleaned from administering hundreds of BCI rehabilitation sessions to stroke patients.•Presents a comprehensive methodology for implementing BCI-based upper extremity therapy in stroke patients.•Provides detailed guidance on the number of sessions, trials, as well as the necessary hardware and software for effective intervention.

Tensor Decomposition Analysis of Longitudinal EEG Signals Reveals Differential Oscillatory Dynamics in Eyes-Closed and Eyes-Open Motor Imagery BCI: A Case Report

Functional dissociation of brain neural activity induced by opening or closing the eyes has been well established. However, how the temporal dynamics of the underlying neuronal modulations differ between these eye conditions during movement-related behaviours is less known. Using a robotic-assisted motor imagery brain-computer interface (MI BCI), we measured neural activity over the motor regions with electroencephalography (EEG) in a stroke survivor during his longitudinal rehabilitation training. We investigated lateralized oscillatory sensorimotor rhythm modulations while the patient imagined moving his hemiplegic hand with closed and open eyes to control an external robotic splint. In order to precisely identify the main profiles of neural activation affected by MI with eyes-open (MIEO) and eyes-closed (MIEC), a data-driven approach based on parallel factor analysis (PARAFAC) tensor decomposition was employed. Using the proposed framework, a set of narrow-band, subject-specific sensorimotor rhythms was identified; each of them had its own spatial and time signature. When MIEC trials were compared with MIEO trials, three key narrow-band rhythms whose peak frequencies centred at ∼8.0 Hz, ∼11.5 Hz, and ∼15.5 Hz, were identified with differently modulated oscillatory dynamics during movement preparation, initiation, and completion time frames. Furthermore, we observed that lower and higher sensorimotor oscillations represent different functional mechanisms within the MI paradigm, reinforcing the hypothesis that rhythmic activity in the human sensorimotor system is dissociated. Leveraging PARAFAC, this study achieves remarkable precision in estimating latent sensorimotor neural substrates, aiding the investigation of the specific functional mechanisms involved in the MI process.

EEGSym: Overcoming Inter-Subject Variability in Motor Imagery Based BCIs With Deep Learning

In this study, we present a new Deep Learning (DL) architecture for Motor Imagery (MI) based Brain Computer Interfaces (BCIs) called EEGSym. Our implementation aims to improve previous state-of-the-art performances on MI classification by overcoming inter-subject variability and reducing BCI inefficiency, which has been estimated to affect 10-50% of the population. This convolutional neural network includes the use of inception modules, residual connections and a design that introduces the symmetry of the brain through the mid-sagittal plane into the network architecture. It is complemented with a data augmentation technique that improves the generalization of the model and with the use of transfer learning across different datasets. We compare EEGSym's performance on inter-subject MI classification with ShallowConvNet, DeepConvNet, EEGNet and EEG-Inception. This comparison is performed on 5 publicly available datasets that include left or right hand motor imagery of 280 subjects. This population is the largest that has been evaluated in similar studies to date. EEGSym significantly outperforms the baseline models reaching accuracies of 88.6±9.0 on Physionet, 83.3±9.3 on OpenBMI, 85.1±9.5 on Kaya2018, 87.4±8.0 on Meng2019 and 90.2±6.5 on Stieger2021. At the same time, it allows 95.7% of the tested population (268 out of 280 users) to reach BCI control (≥70% accuracy). Furthermore, these results are achieved using only 16 electrodes of the more than 60 available on some datasets. Our implementation of EEGSym, which includes new advances for EEG processing with DL, outperforms previous state-of-the-art approaches on inter-subject MI classification.

Event-Related Potentials Analysis of the Effects of Discontinuous Short-Term Fine Motor Imagery on Motor Execution

In this study, event-related potentials and neurobehavioral measurements were used to investigate the effects of discontinuous short-term fine motor imagery (MI), a paradigm of finger sequential MI training interspersed with no-MI that occurs within 1 hr, on fine finger motor execution. The event-related potentials revealed that there were significant differences in the P300 between the fine MI training and the no-MI training. There were also significant changes in the P200 between fine motor execution of familiar tasks after MI training and fine motor execution of unfamiliar tasks without MI training. Neurobehavioral data revealed that the fine MI enhanced fine motor execution. These findings may suggest that discontinuous short-term fine MI could be useful in improving fine motor skills.

Robot Assisted Treatment of Hand Functional Rehabilitation Based on Visual Motor Imagination

This pilot study implements a hybrid brain computer interface paradigm based on motor imagery (MI) and steady-state visual evoked potential (SSVEP), in order to explore the neural mechanism and clinical effect of MI-SSVEP intervention paradigm on upper limb functional rehabilitation. In this study, EEG data of 12 healthy participants were collected, and the activation regions of MI-SSVEP paradigm were identified by power spectral density (PSD). By analyzing the inter trial phase consistency (ITPC) of characteristic regions and the causal relationship of brain network, the motor cognitive process including high-level somatosensory joint cortex in the intervention process of MI-SSVEP was studied. Subsequently, this study verified the clinical effect of MI-SSVEP intervention paradigm for 61 stroke patients. The results show that the robot assisted therapy using MI-SSVEP intervention paradigm can more effectively improve the rehabilitation effect of patients.

Neural correlates of unpredictable Stop and non‐Stop cues in overt and imagined execution

The ability to inhibit incorrect behaviors is crucial for survival. In real contexts, cues that require stopping usually appear intermixed with indications to continue the ongoing action. However, in the classical Stop‐signal task (SST), the unpredictable stimuli are always signals that require inhibition. To understand the neural mechanisms activated by low‐probability nonstop cues, we recorded the electroencephalography from 23 young volunteers while they performed a modified SST where the unpredictable stimuli could be either Stop or confirmatory Go signals (CGo). To isolate the influence of motor output, the SST was performed during overt and covert execution. We found that, paradoxically, CGo stimuli activated motor inhibition processes, and evoked patterns of brain activity similar to those obtained after Stop signals (N2/P3 event‐related potentials and midfrontal theta power increase), though in lesser magnitude. These patterns were also observed during the imagined performance. Finally, applying machine learning procedures, we found that the brain activity evoked after CGo versus Stop signals can be classified above chance during both, overt and imagined execution. Our results provide evidence that unpredictable signals cause motor inhibition even when they require to continue an ongoing action.

This study advances our understanding of the neural correlates of inhibition by using a modified Stop‐signal task where Stop signals were intermixed with cues to continue the ongoing action (CGo signals). CGo signals produced motor inhibition and EEG activity similar to Stop signals (both during overt and imagined performance). The neural activity related to CGo vs Stop signals could be decoded using a machine learning algorithm, indicating that Stop signals evoke a specific pattern of EEG activity.

Changes in Corticospinal Circuits During Premovement Facilitation in Physiological Conditions

Changes in corticospinal excitability have been well documented in the preparatory period before movement, however, their mechanisms and physiological role have not been entirely elucidated. We aimed to investigate the functional changes of excitatory corticospinal circuits during a reaction time (RT) motor task (thumb abduction) in healthy subjects (HS). 26 HS received single pulse transcranial magnetic stimulation (TMS) over the primary motor cortex (M1). After a visual go signal, we calculated RT and delivered TMS at three intervals (50, 100, and 150 ms) within RT and before movement onset, recording motor evoked potentials (MEP) from the abductor pollicis brevis (APB) and the task-irrelevant abductor digiti minimi (ADM). We found that TMS increased MEP_APB amplitude when delivered at 150, 100, and 50 ms before movement onset, demonstrating the occurrence of premovement facilitation (PMF). MEP increase was greater at the shorter interval (MEP₅₀) and restricted to APB (no significant effects were detected recording from ADM). We also reported time-dependent changes of the RT and a TMS side-dependent effect on MEP amplitude (greater on the dominant side). In conclusion, we here report changes of RT and side-dependent, selective and facilitatory effects on the MEP_APB amplitude when TMS is delivered before movement onset (PMF), supporting the role of excitatory corticospinal mechanisms at the basis of the selective PMF of the target muscle during the RT protocol.

Brain-Computer Interface Coupled to a Robotic Hand Orthosis for Stroke Patients' Neurorehabilitation: A Crossover Feasibility Study

Brain-Computer Interfaces (BCI) coupled to robotic assistive devices have shown promise for the rehabilitation of stroke patients. However, little has been reported that compares the clinical and physiological effects of a BCI intervention for upper limb stroke rehabilitation with those of conventional therapy. This study assesses the feasibility of an intervention with a BCI based on electroencephalography (EEG) coupled to a robotic hand orthosis for upper limb stroke rehabilitation and compares its outcomes to conventional therapy. Seven subacute and three chronic stroke patients (M = 59.9 ± 12.8) with severe upper limb impairment were recruited in a crossover feasibility study to receive 1 month of BCI therapy and 1 month of conventional therapy in random order. The outcome measures were comprised of: Fugl-Meyer Assessment of the Upper Extremity (FMA-UE), Action Research Arm Test (ARAT), motor evoked potentials elicited by transcranial magnetic stimulation (TMS), hand dynamometry, and EEG. Additionally, BCI performance and user experience were measured. All measurements were acquired before and after each intervention. FMA-UE and ARAT after BCI (23.1 ± 16; 8.4 ± 10) and after conventional therapy (21.9 ± 15; 8.7 ± 11) were significantly higher (p < 0.017) compared to baseline (17.5 ± 15; 4.3 ± 6) but were similar between therapies (p > 0.017). Via TMS, corticospinal tract integrity could be assessed in the affected hemisphere of three patients at baseline, in five after BCI, and four after conventional therapy. While no significant difference (p > 0.05) was found in patients’ affected hand strength, it was higher after the BCI therapy. EEG cortical activations were significantly higher over motor and non-motor regions after both therapies (p < 0.017). System performance increased across BCI sessions, from 54 (50, 70%) to 72% (56, 83%). Patients reported moderate mental workloads and excellent usability with the BCI. Outcome measurements implied that a BCI intervention using a robotic hand orthosis as feedback has the potential to elicit neuroplasticity-related mechanisms, similar to those observed during conventional therapy, even in a group of severely impaired stroke patients. Therefore, the proposed BCI system could be a suitable therapy option and will be further assessed in clinical trials.

A novel paired associative stimulation protocol with a high-frequency peripheral component: A review on results in spinal cord injury rehabilitation

In recent decades, a multitude of therapeutic approaches has been developed for spinal cord injury (SCI), but few have progressed to regular clinical practice. Novel non-invasive, cost-effective, and feasible approaches to treat this challenging condition are needed. A novel variant of paired associative stimulation (PAS), high-PAS, consists of non-invasive high-intensity transcranial magnetic stimulation (TMS) and non-invasive high-frequency electrical peripheral nerve stimulation (PNS). We observed a therapeutic effect of high-PAS in 20 patients with incomplete SCI with wide range of injury severity, age, and time since injury. Tetraplegic and paraplegic, traumatic, and neurological SCI patients benefited from upper- or lower-limb high-PAS. We observed increases in manual motor scores (MMT) of upper and lower limbs, functional hand tests, walking tests, and measures of functional independence. We also optimized PAS settings in several studies in healthy subjects and began elucidating the mechanisms of therapeutic action. The scope of this review is to describe the clinical experience gained with this novel PAS approach. This review is focused on the summary of our results and observations and the methodological considerations for researchers and clinicians interested in adopting and further developing this new method.

Omitting TMS component from paired associative stimulation with high-frequency PNS: A case series of tetraplegic patients

Objectives

Earlier studies have shown how chronic spinal cord injury (SCI) patients have benefitted from paired associative stimulation (PAS), consisting of high-frequency peripheral nerve stimulation (PNS) and high-intensity transcranial magnetic stimulation (TMS). Since high-frequency PNS is poorly characterized, its therapeutic effect without TMS should be evaluated. We tested the effect of PNS combined with motor imagery in chronic SCI patients using the same parameters of PNS as in earlier PAS-based studies that also used TMS.

Methods

Five patients with chronic incomplete SCI and tetraplegia received a 6-week treatment of PNS combined with motor imagery to the weaker upper limb. Patients were evaluated with Manual Muscle Testing (MMT), hand function tests (Box and block, grip and pinch strength dynamometry), and spasticity.

Results

There was no significant change in hand function tests or spasticity. MMT values improved significantly immediately after the PNS period (0.59 ± 0.17, p = 0.043) and in the 1-month follow-up visit (0.87 ± 0.18, p = 0.043). However, improvement of MMT values was weaker than in chronic tetraplegic patients in a corresponding PAS study that used identical PNS stimulation but also included the TMS component omitted here (Tolmacheva et al., 2019a, Clin Neurophysiol Pract).

Conclusions

The lack of effect on functional hand tests with the protocol presented here suggests that the synergistic effect of PNS and TMS components is essential for the full therapeutic effect previously observed with PAS intervention. The moderate improvement of the MMT score suggests the possible usefulness of PNS and motor imagery for some of those tetraplegic SCI patients who have contraindications to TMS.

Significance

These results add to the understanding of the PAS therapeutic mechanism by highlighting the importance of dual stimulation for achieving the full therapeutic effect of long-term PAS with a high-frequency PNS component.

Using Transcranial Direct Current Stimulation to Augment the Effect of Motor Imagery-Assisted Brain-Computer Interface Training in Chronic Stroke Patients-Cortical Reorganization Considerations

Introduction: Transcranial direct current stimulation (tDCS) has been shown to modulate cortical plasticity, enhance motor learning and post-stroke upper extremity motor recovery. It has also been demonstrated to facilitate activation of brain-computer interface (BCI) in stroke patients. We had previously demonstrated that BCI-assisted motor imagery (MI-BCI) can improve upper extremity impairment in chronic stroke participants. This study was carried out to investigate the effects of priming with tDCS prior to MI-BCI training in chronic stroke patients with moderate to severe upper extremity paresis and to investigate the cortical activity changes associated with training. Methods: This is a double-blinded randomized clinical trial. Participants were randomized to receive 10 sessions of 20-min 1 mA tDCS or sham-tDCS before MI-BCI, with the anode applied to the ipsilesional, and the cathode to the contralesional primary motor cortex (M1). Upper extremity sub-scale of the Fugl-Meyer Assessment (UE-FM) and corticospinal excitability measured by transcranial magnetic stimulation (TMS) were assessed before, after and 4 weeks after intervention. Results: Ten participants received real tDCS and nine received sham tDCS. UE-FM improved significantly in both groups after intervention. Of those with unrecordable motor evoked potential (MEP-) to the ipsilesional M1, significant improvement in UE-FM was found in the real-tDCS group, but not in the sham group. Resting motor threshold (RMT) of ipsilesional M1 decreased significantly after intervention in the real-tDCS group. Short intra-cortical inhibition (SICI) in the contralesional M1 was reduced significantly following intervention in the sham group. Correlation was found between baseline UE-FM score and changes in the contralesional SICI for all, as well as between changes in UE-FM and changes in contralesional RMT in the MEP- group. Conclusion: MI-BCI improved the motor function of the stroke-affected arm in chronic stroke patients with moderate to severe impairment. tDCS did not confer overall additional benefit although there was a trend toward greater benefit. Cortical activity changes in the contralesional M1 associated with functional improvement suggests a possible role for the contralesional M1 in stroke recovery in more severely affected patients. This has important implications in designing neuromodulatory interventions for future studies and tailoring treatment. Clinical Trial Registration: The study was registered at https://clinicaltrials.gov (NCT01897025).

Motor Imagery Training During Arm Immobilization Prevents Corticomotor Idling: An EEG Resting-State Analysis

Limb disuse causes overt, measurable alterations in motor functions. Motor imagery (MI) practice has been used as a behavioral strategy to prevent motor impairments due to limb disuse or immobilization. Yet, how MI operates at the neural level in the context of short-term limb immobilization remains understudied. We hypothesized that MI treatment applied during 12 h of arm immobilization prevents immobilization-related changes in resting-state electroencephalographic (rsEEG) power and functional connectivity. Fourteen participants first underwent rsEEG after 12 h of normal motor activity (without immobilization). Then, rsEEG recording was performed after 12 h of arm immobilization either with MI treatment or without, each condition separated by 1 week, according to a randomized within-subjects design. MI treatment consisted in performing varied visual and kinaesthetic MI exercises (5 sessions of 15 min every two hours). The results showed that in the delta, theta, alpha and beta frequency bands, interhemispheric difference in sensors power over the motor cortex (i.e. C3 vs. C4) was reduced after arm immobilization, while it did not change when MI treatment was delivered during the immobilization period. Moreover, functional connectivity across the sensors-network in the delta (1-4 Hz) and alpha (8-12 Hz) frequency bands decreased after immobilization while it was restored by MI treatment. To conclude, MI counteracts functional neural changes within and between motor regions in the context of limb immobilization. Practical applications for motor rehabilitation strategies, particularly in stroke patients, are also discussed.

Brain-computer interface performance analysis of monozygotic twins with discordant hand dominance: A case study

Brain-computer interfaces (BCI) decode user's intentions to control external devices. However, performance variations across individuals have limited their use to laboratory environments. Handedness could contribute to these variations, especially when motor imagery (MI) tasks are used for BCI control. To further understand how handedness affects BCI control, performance differences between two monozygotic twins were analysed during offline movement and MI tasks, and while twins controlled a BCI using right-hand MI. Quantitative electroencephalography (qEEG), brain structures' volumes, and neuropsychological tests were assessed to evaluate physiological, anatomical and psychological relationships with BCI performance. Results showed that both twins had good motor imagery and attention abilities, similar volumes on most subcortical brain structures, more pronounced event-related desynchronization elicited by the twin performing non-dominant MI, and that this twin also obtained significant higher performances with the BCI. Linear regression analysis implied a strong association between twins' BCI performance, and more pronounced cortical activations in the contralateral hemisphere relative to hand MI. Therefore, it is possible that BCI performance was related with the ability of each twin to elicit cortical activations during hand MI, and less associated with subcortical brain structures' volumes and neuropsychological tests.

Acquisition and consolidation of implicit motor learning with physical and mental practice across multiple days of anodal tDCS

BACKGROUND

Acquisition and consolidation of a new motor skill occurs gradually over long time span. Motor imagery (MI) and brain stimulation have been showed as beneficial approaches that boost motor learning, but little is known about the extent of their combined effects.

OBJECTIVE

Here, we aimed to investigate, for the first time, whether delivering multiple sessions of transcranial direct current stimulation (tDCS) over primary motor cortex during physical and MI practice might improve implicit motor sequence learning in a young population.

METHODS

Participants practiced a serial reaction time task (SRTT) either physically or through MI, and concomitantly received either an anodal (excitatory) or sham stimulation over the primary motor cortex during three successive days. The effect of anodal tDCS on the general motor skill and sequence specific learning were assessed on both acquisition (within-day) and consolidation (between-day) processes. We further compared the magnitude of motor learning reached after a single and three daily sessions of tDCS.

RESULTS

The main finding showed that anodal tDCS boosted MI practice, but not physical practice, during the first acquisition session. A second major result showed that compared to sham stimulation, multiple daily session of anodal tDCS, for both types of practice, resulted in greater implicit motor sequence learning rather than a single session of stimulation.

CONCLUSIONS

The present study is of particular importance in the context of rehabilitation, where we postulate that scheduling mental training when patients are not able to perform physical movement might beneficiate from concomitant and consecutive brain stimulation sessions over M₁ to promote functional recovery.

Gamma-Band Oscillations Preferential for Nociception can be Recorded in the Human Insula

Transient nociceptive stimuli elicit robust phase-locked local field potentials (LFPs) in the human insula. However, these responses are not preferential for nociception, as they are also elicited by transient non-nociceptive vibrotactile, auditory, and visual stimuli. Here, we investigated whether another feature of insular activity, namely gamma-band oscillations (GBOs), is preferentially observed in response to nociceptive stimuli. Although nociception-evoked GBOs have never been explored in the insula, previous scalp electroencephalography and magnetoencephalography studies suggest that nociceptive stimuli elicit GBOs in other areas such as the primary somatosensory and prefrontal cortices, and that this activity could be closely related to pain perception. Furthermore, tracing studies showed that the insula is a primary target of spinothalamic input. Using depth electrodes implanted in 9 patients investigated for epilepsy, we acquired insular responses to brief thermonociceptive stimuli and similarly arousing non-nociceptive vibrotactile, auditory, and visual stimuli (59 insular sites). As compared with non-nociceptive stimuli, nociceptive stimuli elicited a markedly stronger enhancement of GBOs (150-300 ms poststimulus) at all insular sites, suggesting that this feature of insular activity is preferential for thermonociception. Although this activity was also present in temporal and frontal regions, its magnitude was significantly greater in the insula as compared with these other regions.

Does Transcranial Direct Current Stimulation Affect the Learning of a Fine Sequential Hand Motor Skill with Motor Imagery?

Learning a fine sequential hand motor skill, like playing the piano or learning to type, improves not only due to physical practice, but also due to motor imagery. Previous studies revealed that transcranial direct current stimulation (tDCS) and motor imagery independently affect motor learning. In the present study, we investigated whether tDCS combined with motor imagery above the primary motor cortex influences sequence-specific learning. Four groups of participants were involved: an anodal, cathodal, sham stimulation, and a control group (without stimulation). A modified discrete sequence production (DSP) task was employed: the Go/NoGo DSP task. After a sequence of spatial cues, a response sequence had to be either executed, imagined, or withheld. This task allows to estimate both non-specific learning and sequence-specific learning effects by comparing the execution of unfamiliar sequences, familiar imagined, familiar withheld, and familiar executed sequences in a test phase. Results showed that the effects of anodal tDCS were already developing during the practice phase, while no effects of tDCS on sequence-specific learning were visible during the test phase. Results clearly showed that motor imagery itself influences sequence learning, but we also revealed that tDCS does not increase the influence of motor imagery on sequence learning.

Hand Rehabilitation Robotics on Poststroke Motor Recovery

The recovery of hand function is one of the most challenging topics in stroke rehabilitation. Although the robot-assisted therapy has got some good results in the latest decades, the development of hand rehabilitation robotics is left behind. Existing reviews of hand rehabilitation robotics focus either on the mechanical design on designers' view or on the training paradigms on the clinicians' view, while these two parts are interconnected and both important for designers and clinicians. In this review, we explore the current literature surrounding hand rehabilitation robots, to help designers make better choices among varied components and thus promoting the application of hand rehabilitation robots. An overview of hand rehabilitation robotics is provided in this paper firstly, to give a general view of the relationship between subjects, rehabilitation theories, hand rehabilitation robots, and its evaluation. Secondly, the state of the art hand rehabilitation robotics is introduced in detail according to the classification of the hardware system and the training paradigm. As a result, the discussion gives available arguments behind the classification and comprehensive overview of hand rehabilitation robotics.

To What Extent Can Motor Imagery Replace Motor Execution While Learning a Fine Motor Skill?

Motor imagery is generally thought to share common mechanisms with motor execution. In the present study, we examined to what extent learning a fine motor skill by motor imagery may substitute physical practice. Learning effects were assessed by manipulating the proportion of motor execution and motor imagery trials. Additionally, learning effects were compared between participants with an explicit motor imagery instruction and a control group. A Go/NoGo discrete sequence production (DSP) task was employed, wherein a five-stimulus sequence presented on each trial indicated the required sequence of finger movements after a Go signal. In the case of a NoGo signal, participants either had to imagine carrying out the response sequence (the motor imagery group), or the response sequence had to be withheld (the control group). Two practice days were followed by a final test day on which all sequences had to be executed. Learning effects were assessed by computing response times (RTs) and the percentages of correct responses (PCs). The electroencephalogram (EEG ) was additionally measured on this test day to examine whether motor preparation and the involvement of visual short term memory (VST M) depended on the amount of physical/mental practice. Accuracy data indicated strong learning effects. However, a substantial amount of physical practice was required to reach an optimal speed. EEG results suggest the involvement of VST M for sequences that had less or no physical practice in both groups. The absence of differences between the motor imagery and the control group underlines the possibility that motor preparation may actually resemble motor imagery.

The influence of motor imagery on the learning of a fine hand motor skill

Motor imagery has been argued to affect the acquisition of motor skills. The present study examined the specificity of motor imagery on the learning of a fine hand motor skill by employing a modified discrete sequence production task: the Go/NoGo DSP task. After an informative cue, a response sequence had either to be executed, imagined, or withheld. To establish learning effects, the experiment was divided into a practice phase and a test phase. In the latter phase, we compared mean response times and accuracy during the execution of unfamiliar sequences, familiar imagined sequences, and familiar executed sequences. The electroencephalogram was measured in the practice phase to compare activity between motor imagery, motor execution, and a control condition in which responses should be withheld. Event-related potentials (ERPs) and event-related lateralizations (ERLs) showed strong similarities above cortical motor areas on trials requiring motor imagery and motor execution, while a major difference was found with trials on which the response sequence should be withheld. Behavioral results from the test phase showed that response times and accuracy improved after physical and mental practice relative to unfamiliar sequences (so-called sequence-specific learning effects), although the effect of motor learning by motor imagery was smaller than the effect of physical practice. These findings confirm that motor imagery also resembles motor execution in the case of a fine hand motor skill.

Functional Equivalence of Imagined vs. Real Performance of an Inhibitory Task: An EEG/ERP Study

Early neuroimaging and electrophysiological studies suggested that motor imagery recruited a different network than motor execution. However, several studies have provided evidence for the involvement of the same circuits in motor imagery tasks, in the absence of overt responses. The present study aimed to test whether imagined performance of a stop-signal task produces a similar pattern of motor-related EEG activity than that observed during real performance. To this end, mu and beta event-related desynchronization (ERD) and the Lateralized Readiness Potential (LRP) were analyzed. The study also aimed to clarify the functional significance of the Stop-N2 and Stop-P3 event-related potential (ERPs) components, which were also obtained during both real and imagined performance. The results showed a common pattern of brain electrical activity, and with a similar time course, during covert performance and overt execution of the stop-signal task: presence of LRP and Stop-P3 in the imagined condition and identical LRP onset, and similar mu and beta ERD temporal windows for both conditions. These findings suggest that a similar inhibitory network may be activated during both overt and covert execution of the task. Therefore, motor imagery may be useful to improve inhibitory skills and to develop new communicating systems for Brain-Computer Interface (BCI) devices based on inhibitory signals.

The dissociation between command following and communication in disorders of consciousness: an fMRI study in healthy subjects

Neuroimaging studies have identified a subgroup of patients with a Disorder of Consciousness (DOC) who, while being behaviorally non-responsive, are nevertheless able to follow commands by modulating their brain activity in motor imagery (MI) tasks. These techniques have even allowed for binary communication in a small number of DOC patients. However, the majority of patients who can follow commands are unable to use their responses to communicate. A similar dissociation between present command following (CF) and absent communication abilities has been reported in overt behavioral assessments. However, the neural correlates of this dissociation in both overt and covert modalities are unknown. Here, we used functional magnetic resonance imaging (fMRI) to explore the neural mechanisms underlying CF and selection of responses for binary communication using either executed or imagined movements. Fifteen healthy participants executed or imagined two different types of arm movements that were either pre-determined by the experimenters (CF) or decided by them (action selection, AS). Action selection involved greater activity in high-level associative areas in frontal and parietal regions than CF. Additionally, motor execution (ME), as compared to MI, activated contralateral motor cortex, while the opposite contrast revealed activation in the ipsilateral sensorimotor cortex and the left inferior frontal gyrus. Importantly, there was no interaction between the task (CF/AS) and modality (MI/ME). Our results suggest that the neural processes involved in following a motor command or selecting between two motor actions are not dependent on how the response is expressed (via ME/MI). They also suggest a potential neural basis for the distinction in cognitive abilities seen in DOC patients.

Neural processes mediating the preparation and release of focal motor output are suppressed or absent during imagined movement

Movements that are executed or imagined activate a similar subset of cortical regions, but the extent to which this activity represents functionally equivalent neural processes is unclear. During preparation for an executed movement, presentation of a startling acoustic stimulus (SAS) evokes a premature release of the planned movement with the spatial and temporal features of the tasks essentially intact. If imagined movement incorporates the same preparatory processes as executed movement, then a SAS should release the planned movement during preparation. This hypothesis was tested using an instructed-delay cueing paradigm during which subjects were required to rapidly release a handheld weight while maintaining the posture of the arm or to perform first-person imagery of the same task while holding the weight. In a subset of trials, a SAS was presented at 1500, 500, or 200 ms prior to the release cue. Task-appropriate preparation during executed and imagined movements was confirmed by electroencephalographic recording of a contingent negative variation waveform. During preparation for executed movement, a SAS often resulted in premature release of the weight with the probability of release progressively increasing from 24 % at -1500 ms to 80 % at -200 ms. In contrast, the SAS rarely (<2 % of trials) triggered a release of the weight during imagined movement. However, the SAS frequently evoked the planned postural response (suppression of bicep brachii muscle activity) irrespective of the task or timing of stimulation (even during periods of postural hold without preparation). These findings provide evidence that neural processes mediating the preparation and release of the focal motor task (release of the weight) are markedly attenuated or absent during imagined movement and that postural and focal components of the task are prepared independently.

Sensorimotor Learning Enhances Expectations During Auditory Perception

Sounds that have been produced with one's own motor system tend to be remembered better than sounds that have only been perceived, suggesting a role of motor information in memory for auditory stimuli. To address potential contributions of the motor network to the recognition of previously produced sounds, we used event-related potential, electric current density, and behavioral measures to investigate memory for produced and perceived melodies. Musicians performed or listened to novel melodies, and then heard the melodies either in their original version or with single pitch alterations. Production learning enhanced subsequent recognition accuracy and increased amplitudes of N200, P300, and N400 responses to pitch alterations. Premotor and supplementary motor regions showed greater current density during the initial detection of alterations in previously produced melodies than in previously perceived melodies, associated with the N200. Primary motor cortex was more strongly engaged by alterations in previously produced melodies within the P300 and N400 timeframes. Motor memory traces may therefore interface with auditory pitch percepts in premotor regions as early as 200 ms following perceived pitch onsets. Outcomes suggest that auditory-motor interactions contribute to memory benefits conferred by production experience, and support a role of motor prediction mechanisms in the production effect.

Is motor-imagery brain-computer interface feasible in stroke rehabilitation?

In the past 3 decades, interest has increased in brain-computer interface (BCI) technology as a tool for assisting, augmenting, and rehabilitating sensorimotor functions in clinical populations. Initially designed as an assistive device for partial or total body impairments, BCI systems have since been explored as a possible adjuvant therapy in the rehabilitation of patients who have had a stroke. In particular, BCI systems incorporating a robotic manipulanda to passively manipulate affected limbs have been studied. These systems can use a range of invasive (ie, intracranial implanted electrodes) or noninvasive neurophysiologic recording techniques (ie, electroencephalography [EEG], near-infrared spectroscopy, and magnetoencephalography) to establish communication links between the brain and the BCI system. Trials are most commonly performed on EEG-based BCI in comparison with the other techniques because of its high temporal resolution, relatively low setup costs, portability, and noninvasive nature. EEG-based BCI detects event-related desynchronization/synchronization in sensorimotor oscillatory rhythms associated with motor imagery (MI), which in turn drives the BCI. Previous evidence suggests that the process of MI preferentially activates sensorimotor regions similar to actual task performance and that repeated practice of MI can induce plasticity changes in the brain. It is therefore postulated that the combination of MI and BCI may augment rehabilitation gains in patients who have had a stroke by activating corticomotor networks via MI and providing sensory feedback from the affected limb using end-effector robots. In this review we examine the current literature surrounding the feasibility of EEG-based MI-BCI systems in stroke rehabilitation. We also discuss the limitations of using EEG-based MI-BCI in patients who have had a stroke and suggest possible solutions to overcome these limitations.

Aging in movement representations for sequential finger movements: a comparison between young-, middle-aged, and older adults

Studies show that as we enter older adulthood (>64years), our ability to mentally represent action in the form of using motor imagery declines. Using a chronometry paradigm to compare the movement duration of imagined and executed movements, we tested young-, middle-aged, and older adults on their ability to perform sequential finger (fine-motor) movements. The task required number recognition and ordering and was presented in three levels of complexity. Results for movement duration indicated no differences between young- and middle-aged adults, however both performed faster than the older group. In regard to the association between imagined and executed actions, correlation analyses indicated that values for all groups were positive and moderate (r's .80,.76,.70). In summary, whereas the older adults were significantly slower in processing actions than their younger counterparts, the ability to mentally represent their actions was similar.

Cue-induced beta rebound during withholding of overt and covert foot movement

OBJECTIVE

Beta rebound is the term for bursts of EEG activity in the beta band observable after movement or somatosensory stimulation. It is assumed to reflect an active inhibition process. Our aim was to investigate the differences in the beta rebound between movement termination and withholding of movement, and the withholding of overt and covert movement.

METHODS

Twenty healthy persons completed Go/NoGo experiments with real and imaginary foot movements (dorsiflexion of both feet). Only participants that presented a beta rebound were considered. Event-related (de)synchronization provided the time course of the beta rebound from a participant specific frequency band. Statistical analyses revealed the significant differences between pairs of conditions: motor execution Go vs. motor execution NoGo, and motor execution NoGo vs. motor imagery NoGo.

RESULTS

The beta rebound is stronger and lasts longer after termination of movement than during withholding of a motor response (9 participants). Withholding of overt movement generates a stronger, longer, and more widespread beta rebound than the withholding of imaginary movement (7 participants). The beta rebound is more common after termination (16/16) and withholding of real movement (12/16) than during withholding of imaginary movements (7/16).

CONCLUSIONS

These phenomena share a common origin and a common frequency band. Their functional meaning is assumed to be the same, although there are differences in time span and intensity of the beta ERS.

SIGNIFICANCE

First direct comparison of the beta rebound between motor execution and motor withholding, as well as withholding of overt and covert foot movement. A beta rebound also occurs during withholding of a motor task, and it is more common and strong for overt movement than for covert movement.

Rehabilitation of gait after stroke: a review towards a top-down approach

This document provides a review of the techniques and therapies used in gait rehabilitation after stroke. It also examines the possible benefits of including assistive robotic devices and brain-computer interfaces in this field, according to a top-down approach, in which rehabilitation is driven by neural plasticity.The methods reviewed comprise classical gait rehabilitation techniques (neurophysiological and motor learning approaches), functional electrical stimulation (FES), robotic devices, and brain-computer interfaces (BCI).From the analysis of these approaches, we can draw the following conclusions. Regarding classical rehabilitation techniques, there is insufficient evidence to state that a particular approach is more effective in promoting gait recovery than other. Combination of different rehabilitation strategies seems to be more effective than over-ground gait training alone. Robotic devices need further research to show their suitability for walking training and their effects on over-ground gait. The use of FES combined with different walking retraining strategies has shown to result in improvements in hemiplegic gait. Reports on non-invasive BCIs for stroke recovery are limited to the rehabilitation of upper limbs; however, some works suggest that there might be a common mechanism which influences upper and lower limb recovery simultaneously, independently of the limb chosen for the rehabilitation therapy. Functional near infrared spectroscopy (fNIRS) enables researchers to detect signals from specific regions of the cortex during performance of motor activities for the development of future BCIs. Future research would make possible to analyze the impact of rehabilitation on brain plasticity, in order to adapt treatment resources to meet the needs of each patient and to optimize the recovery process.

Role of the primary motor cortex in the early boost in performance following mental imagery training

Recently, it has been suggested that the primary motor cortex (M1) plays a critical role in implementing the fast and transient post-training phase of motor skill consolidation, known to yield an early boost in performance. Whether a comparable early boost in performance occurs following motor imagery (MIM) training is still unknown. To address this issue, two groups of subjects learned a finger tapping sequence either by MIM or physical practice (PP). In both groups, performance increased significantly in the post-training phase when compared with the pre-training phase and further increased after a 30 min resting period, indicating that both MIM and PP trainings were equally efficient and induced an early boost in motor performance. This conclusion was corroborated by the results of an additional control group. In a second experiment, we then investigated the causal role of M1 in implementing the early boost process resulting from MIM training. To do so, we inhibited M1 by applying a continuous theta-burst stimulation (cTBS) in healthy volunteers just after they learnt, by MIM, the same finger-tapping task as in Experiment #1. As a control, cTBS was applied over the vertex of subjects who underwent the same experiment. We found that cTBS applied over M1 selectively abolished the early boost process subsequent to MIM training. Altogether, the present study provides evidence that MIM practice induces an early boost in performance and demonstrates that M1 is causally involved in this process. These findings further divulge some degree of behavioral and neuronal similitude between MIM and PP.

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.

Functional magnetic resonance imaging study on the effects of acute single administration of paroxetine on motivation-related brain activity

AIM

The aim of the present study was to investigate the effects of acute paroxetine administration on brain activity related to motivation.

METHODS

Sixteen healthy subjects participated in a randomized, single-blind, no-drug/placebo-controlled, cross-over study. After administration of no drug, placebo or paroxetine (selective serotonin reuptake inhibitor; 20 mg), subjects underwent functional magnetic resonance imaging while performing a monetary incentive delay task. We analyzed the differences in brain activities of the reward anticipation/motor preparation period that are subject to motivational modulation. For this purpose, we subdivided the incentive trials on the basis of whether the reaction times (RT) were slower or faster than the subject's mean RT (slow RT and fast RT trials).

RESULTS

No drug and placebo showed robust activation differences in the globus pallidus and putamen for the fast RT trials compared to the slow RT trials, whereas paroxetine showed none. Paroxetine showed significantly lower activations in the globus pallidus, insula, putamen and dorsolateral prefrontal cortex compared to no drug in the fast RT trials.

CONCLUSIONS

Paroxetine single acute administration diminished brain activity induced by motivation in healthy subjects. This may partially explain the increased lack of motivation seen in patients with relatively mild symptoms after taking a dose of paroxetine for the first time.

Premovement facilitation of corticospinal excitability before simple and sequential movement

The purpose of this study was to investigate whether premovement facilitation of corticospinal excitability before sequential movement was different from that before simple movement. Each of 7 participants who performed choice reaction tasks with the right hand pressed a force transducer with the index finger in response to a start cue or pressed the transducers sequentially with the index finger, little finger, thumb, little finger, and index finger. Transcranial magnetic stimulation was delivered to the left motor cortex before the electromyographic burst in the first dorsal interosseous muscle and motor evoked potentials were recorded from the first dorsal interosseous muscle. The amplitude of the motor-evoked potential increased as its onset got closer to the onset of the electromyographic burst. The increase before the sequential movement was larger and began earlier than that before the simple movement. These findings indicate that premovement facilitation of corticospinal excitability is different in magnitude and timing between sequential and simple movements.

Task complexity differentially affects executed and imagined movement preparation: evidence from movement-related potentials

Background

The neural simulation theory predicts similarity for the neural mechanisms subserving overt (motor execution) and covert (movement imagination) actions. Here we tested this prediction for movement preparation, a key characteristic of motor cognition.

Methodology/Principal Findings

High-density electroencephalogram (EEG) was recorded during covert and overt actions. Movement preparation was studied with a motor priming paradigm, which varied task complexity and amount of advance information. Participants performed simple or complex sequential finger movements either overtly or covertly. Advance information was either fully predictive or partially predictive. Stimulus-locked event-related potential (ERP) data showed the typical pattern of foreperiod activation for overt and covert movements. The foreperiod contingent negative variation (CNV) differed between simple and complex movements only in the execution task. ERP topographies differed between execution and imagination only when advance information was fully predictive.

Conclusions/Significance

Results suggest a differential contribution of the movement preparation network to action imagination and execution. Overt and covert actions seem to involve similar though not identical mechanisms, where overt actions engage a more fine-grained modulation of covert preparatory states.

On the equivalence of executed and imagined movements: evidence from lateralized motor and nonmotor potentials

The neural simulation theory assumes that motor imagery and motor execution draw on a shared set of mechanisms underlying motor cognition. Evidence is accumulating that motor imagery and motor execution have many common features. The extent of the similarity and whether it spreads into the preparation phase is however unclear. This study used electroencephalographic recordings to compare the effects of providing advance information about upcoming movements on preparatory processing in a motor imagery and execution paradigm. Event-related potential data were recorded in a priming task where participants were cued to perform simple or complex finger movements. We hypothesized that a high degree of functional similarity of motor imagery and motor execution should be reflected in similar alterations of lateralized preparatory activity. Lateralized preparatory activity was indeed very similar, showing both motor-related (lateralized readiness potential, LRP) and cognitive components (anterior directing-attention negativity or ADAN, late directing-attention positivity or LDAP). Dipole analysis revealed that LRP, ADAN, and LDAP sources were very comparable for motor imagination and execution. Results generally support the idea of common underlying functional networks subserving both the preparation for execution and imagery of movements. They also provide a broader context for this notion by revealing similarities in cognitive components associated with the movement tasks.

Exploiting multiple sensory modalities in brain-machine interfaces

Recent improvements in cortically-controlled brain-machine interfaces (BMIs) have raised hopes that such technologies may improve the quality of life of severely motor-disabled patients. However, current generation BMIs do not perform up to their potential due to the neglect of the full range of sensory feedback in their strategies for training and control. Here we confirm that neurons in the primary motor cortex (MI) encode sensory information and demonstrate a significant heterogeneity in their responses with respect to the type of sensory modality available to the subject about a reaching task. We further show using mutual information and directional tuning analyses that the presence of multi-sensory feedback (i.e. vision and proprioception) during replay of movements evokes neural responses in MI that are almost indistinguishable from those responses measured during overt movement. Finally, we suggest how these playback-evoked responses may be used to improve BMI performance.

Observation-based learning for brain-machine interfaces

Canonically, 'mirror neurons' are cells in area F5 of the ventral premotor cortex that are active during both observation and execution of goal-directed movements. Recently, cells with similar properties have been observed in a number of other areas in the motor system, including the primary motor cortex. Mirror neurons are a part of a system whose function is thought to involve the prediction and interpretation of the sensory consequences of our own actions as well as the actions of others. Mirror-like responses are relevant to the development of brain-machine interfaces (BMIs) because they provide a robust way to map neural activity to behavior, and because they represent high-level information about goals and intentions that may have utility in future BMI applications.