Showing papers on "Motor imagery published in 2005"

Common Spatial Pattern Method for Channel Selelction in Motor Imagery Based Brain-computer Interface

Abstract: A brain-computer interface (BCI) based on motor imagery (MI) translates the subject's motor intention into a control signal through classifying the electroencephalogram (EEG) patterns of different imagination tasks, e.g. hand and foot movements. Characteristic EEG spatial patterns make MI tasks substantially discriminable. Multi-channel EEGs are usually necessary for spatial pattern identification and therefore MI-based BCI is still in the stage of laboratory demonstration, to some extent, due to the need for constantly troublesome recording preparation. This paper presents a method for channel reduction in Mi-based BCI. Common spatial pattern (CSP) method was employed to analyze spatial patterns of imagined hand and foot movements. Significant channels were selected by searching the maximums of spatial pattern vectors in scalp mappings. A classification algorithm was developed by means of combining linear discriminant analysis towards event-related desynchronization (ERD) and readiness potential (RP). The classification accuracies with four optimal channels were 93.45% and 91.88% for two subjects

Neural Topography and Content of Movement Representations

Abstract: We have used implicit motor imagery to investigate the neural correlates of motor planning independently from actual movements. Subjects were presented with drawings of left or right hands and asked to judge the hand laterality, regardless of the stimulus rotation from its upright orientation. We paired this task with a visual imagery control task, in which subjects were presented with typographical characters and asked to report whether they saw a canonical letter or its mirror image, regardless of its rotation. We measured neurovascular activity with fast event-related fMRI, distinguishing responses parametrically related to motor imagery from responses evoked by visual imagery and other task-related phenomena. By quantifying behavioral and neurovascular correlates of imagery on a trial-by-trial basis, we could discriminate between stimulusrelated, mental rotation-related, and response-related neural activity. We found that specific portions of the posterior parietal and precentral cortex increased their activity as a function of mental rotation only during the motor imagery task. Within these regions, the parietal cortex was visually responsive, whereas the dorsal precentral cortex was not. Response- but not rotation-related activity was found around the left central sulcus (putative primary motor cortex) during both imagery tasks. Our study provides novel evidence on the topography and content of movement representations in the human brain. During intended action, the posterior parietal cortex combines somatosensory and visuomotor information, whereas the dorsal premotor cortex generates the actual motor plan, and the primary motor cortex deals with movement execution. We discuss the relevance of these results in the context of current models of action planning.

What Disconnection Tells about Motor Imagery: Evidence from Paraplegic Patients

Abstract: Brain activation during motor imagery has been the subject of a large number of studies in healthy subjects, leading to divergent interpretations with respect to the role of descending pathways and kinesthetic feedback on the mental rehearsal of movements. We investigated patients with complete spinal cord injury (SCI) to find out how the complete disruption of motor efferents and sensory afferents influences brain activation during motor imagery of the disconnected feet. Eight SCI patients underwent behavioral assessment and functional magnetic resonance imaging. When compared to a healthy population, stronger activity was detected in primary and all non-primary motor cortical areas and subcortical regions. In paraplegic patients the primary motor cortex was consistently activated, even to the same degree as during movement execution in the controls. Motor imagery in SCI patients activated in parallel both the motor execution and motor imagery networks of healthy subjects. In paraplegics the extent of activation in the primary motor cortex and in mesial non-primary motor areas was significantly correlated with the vividness of movement imagery, as assessed by an interview. The present findings provide new insights on the neuroanatomy of motor imagery and the possible role of kinesthetic feedback in the suppression of cortical motor output required during covert movements.

Selective impairment of hand mental rotation in patients with focal hand dystonia

Abstract: Mental rotation of body parts determines activation of cortical and subcortical systems involved in motor planning and execution, such as motor and premotor areas and basal ganglia. These structures are severely impaired in several movement disorders, including dystonia. Writer's cramp is the most common form of focal hand dystonia. This study investigates whether patients affected by writer's cramp present with difficulties in tasks involving mental rotation of body parts and whether any impairments are specific to the affected hand or generalized to other body parts. For this purpose we tested 15 patients with right writer's cramp (aged 21-68 years, 8 women) and 15 healthy control subjects (10 women, age and education matched). Stimuli consisted of realistic photographs of hands and feet presented on a computer monitor in different orientations with respect to the upright canonical orientation. In each trial, subjects gave a laterality judgement by reporting verbally whether the presented body part was left or right. Two main results of the study are, firstly, writer's cramp patients are slower than controls in mentally rotating hands [F (1,28) = 5.4; P = 0.028] but not feet, and secondly, the pattern of response times to stimuli at various orientations suggests that the mental motor imagery of controls and patients reflects the type of processes and mechanisms called into play during actual execution of the same movements. In particular, increased difficulty in rotating right-sided stimuli at 120 degrees and left-sided stimuli at 240 degrees would suggest that mental rotation of body parts reflects the anatomical constraints of real hand movements. In conclusion, patients with writer's cramp presented mental rotation deficits specific to the hand. Importantly, deficits were present during mental rotation of both the right (affected) and the left (unaffected) hand, thus suggesting that the observed alterations may be independent and even exist prior to overt manifestations of dystonia.

Classification of motor imagery tasks for brain-computer interface applications by means of two equivalent dipoles analysis

Abstract: We have developed a novel approach using source analysis for classifying motor imagery tasks. Two-equivalent-dipoles analysis was proposed to aid classification of motor imagery tasks for brain-computer interface (BCI) applications. By solving the electroencephalography (EEG) inverse problem of single trial data, it is found that the source analysis approach can aid classification of motor imagination of left- or right-hand movement without training. In four human subjects, an averaged accuracy of classification of 80% was achieved. The present study suggests the merits and feasibility of applying EEG inverse solutions to BCI applications from noninvasive EEG recordings.

A wavelet-based time?frequency analysis approach for classification of motor imagery for brain?computer interface applications

Abstract: Electroencephalogram (EEG) recordings during motor imagery tasks are often used as input signals for brain-computer interfaces (BCIs). The translation of these EEG signals to control signals of a device is based on a good classification of various kinds of imagination. We have developed a wavelet-based time-frequency analysis approach for classifying motor imagery tasks. Time-frequency distributions (TFDs) were constructed based on wavelet decomposition and event-related (de)synchronization patterns were extracted from symmetric electrode pairs. The weighted energy difference of the electrode pairs was then compared to classify the imaginary movement. The present method has been tested in nine human subjects and reached an averaged classification rate of 78%. The simplicity of the present technique suggests that it may provide an alternative method for EEG-based BCI applications.

Robust EEG channel selection across subjects for brain-computer interfaces

Abstract: Most EEG-based brain-computer interface (BCI) paradigms come along with specific electrode positions, for example, for a visual-based BCI, electrode positions close to the primary visual cortex are used. For new BCI paradigms it is usually not known where task relevant activity can be measured from the scalp. For individual subjects, Lal et al. in 2004 showed that recording positions can be found without the use of prior knowledge about the paradigm used. However it remains unclear to what extent their method of recursive channel elimination (RCE) can be generalized across subjects. In this paper we transfer channel rankings from a group of subjects to a new subject. For motor imagery tasks the results are promising, although cross-subject channel selection does not quite achieve the performance of channel selection on data of single subjects. Although the RCE method was not provided with prior knowledge about the mental task, channels that are well known to be important (from a physiological point of view) were consistently selected whereas task-irrelevant channels were reliably disregarded.

Recognition of motor imagery electroencephalography using independent component analysis and machine classifiers.

Abstract: Motor imagery electroencephalography (EEG), which embodies cortical potentials during mental simulation of left or right finger lifting tasks, can be used to provide neural input signals to activate a brain computer interface (BCI) The effectiveness of such an EEG-based BCI system relies on two indispensable components: distinguishable patterns of brain signals and accurate classifiers This work aims to extract two reliable neural features, termed contralateral and ipsilateral rebound maps, by removing artifacts from motor imagery EEG based on independent component analysis (ICA), and to employ four classifiers to investigate the efficacy of rebound maps Results demonstrate that, with the use of ICA, recognition rates for four classifiers (fisher linear discriminant (FLD), back-propagation neural network (BP-NN), radial-basis function neural network (RBF-NN), and support vector machine (SVM)) improved significantly, from 54%, 54%, 57% and 55% to 705%, 755%, 765% and 773%, respectively In addition, the areas under the receiver operating characteristics (ROC) curve, which assess the quality of classification over a wide range of misclassification costs, also improved from 65, 60, 62, and 64 to 74, 76, 80 and 81, respectively

Observation, imagination and execution of an effortful movement: more evidence for a central explanation of motor imagery

Abstract: In this study subjects had to imagine, observe and perform a series of 25 squat movements while lifting two dumbbells of 12.5 kg each (one with each hand). This movement is effortful and requires substantial activation of peripheral systems. It was asked whether subjects when they imagined that they were performing the movements or when they observed a model performing the squat movements would show increased activity in EMG, heart rate and respiration compared with a control condition where they sat relaxed in a comfortable chair or a condition where they actually performed the squat movements. Two groups of subjects participated in the experiment: experienced squatters and novices. By employing these two groups we were able to study the differential effect of earlier experience with the target movement on peripheral activation. The results showed that with the exception of respiration no significant peripheral activation could be measured related to motor imagery. Although a clear distinction in experience existed between the experienced squatters versus the novices, no relevant imagery-related differences could be obtained between the two groups. The results are discussed in the light of a central explanation of motor imagery.

A brain computer interface with online feedback based on magnetoencephalography

Abstract: The aim of this paper is to show that machine learning techniques can be used to derive a classifying function for human brain signal data measured by magnetoencephalography (MEG), for the use in a brain computer interface (BCI). This is especially helpful for evaluating quickly whether a BCI approach based on electroencephalography, on which training may be slower due to lower signal-to-noise ratio, is likely to succeed. We apply RCE and regularized SVMs to the experimental data of ten healthy subjects performing a motor imagery task. Four subjects were able to use a trained classifier to write a short name. Further analysis gives evidence that the proposed imagination task is suboptimal for the possible extension to a multiclass interface. To the best of our knowledge this paper is the first working online MEG-based BCI and is therefore a "proof of concept".

Disturbance of motor imagery after cerebellar stroke

Abstract: The authors studied the possible involvement of the cerebellum in nonexecutive motor functions needed for a normal performance of complex motor patterns by analyzing (using chronometric evaluation) finger movement sequences and their respective motor imagery (a mental simulation of motor patterns). Patients suffering from a cerebellar stroke (n = 11) were compared with aged-matched control volunteers (n = 11). Patients that had apparently recovered from a unilateral cerebellar stroke showed a marked slowing of motor performance in both hands (ipsi- and contralateral to lesion). This effect was accompanied by a similar slowing of motor imagery, suggesting that the cerebellum, traditionally implicated in the control of motor execution, is also involved in nonexecutive motor functions such as the planning and internal simulation of movements.

EMG activity in selected target muscles during imagery rising on tiptoes in healthy adults and poststroke hemiparetic patients.

Abstract: 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.

Mental rotation in a patient with an implanted electrode grid in the motor cortex.

Abstract: We investigated the effects of cortical stimulation on mental rotation tasks in a patient with an electrode array placed over his left primary motor cortex. The array was implanted to relieve chronic pain resulting from right brachial plexus damage. Tasks involving motor imagery were slowed down by cortical stimulation, whereas those involving visual imagery were not. When the patient performed the motor-imagery task, the interference effect on response times disappeared if the stimulator was switched off. We also probed two of the sites (anterior-lateral and posterior-medial position), and found that stimulation of the more anterior-lateral one consistently disrupted motor imagery.

Sentence Understanding Engages Motor Processes

Abstract: Sentence Understanding Engages Motor Processes Benjamin K. Bergen (Bergen@Hawaii.Edu) Kathryn B. Wheeler (Kwheeler@Hawaii.Edu) Department of Linguistics, 569 Moore Hall, 1890 East West Road, Honolulu, HI 96822 USA Abstract running a mental simulation of a described scene, wherein an understander activates motor representations corresponding to what participants in the scene might do and perceptual representations of images they might perceive. The reasoning behind this is straightforward. Perceptual and motor imagery are known to play critical roles in higher cognitive functions like memory (Wheeler et al. 2000, Nyberg et al. 2001). By extension, they may well be integral to language understanding as well. On this view, viable communication involves the successful evocation of an aligned set of perceptual and motor images in the mind of a hearer (Glenberg & Robertson 1999, Bergen & Chang 2005). Recent evidence from neuroscience suggests a mechanism by which the internal imagination of a scene described by language may be effected. Two studies provide evidence that processing motion language associated with particular body parts also results in the activation of areas of motor and pre-motor cortex involved in producing motor actions associated with those same effectors. Using both behavioral and neurophysiological evidence, Pulvermuller et al. (2001) found that verbs associated with different effectors (mouth, hand, leg) were processed at different rates and in different regions of motor cortex. More recently, Tettamanti et al. (m.s.) have shown through an imaging study that passive listening to sentences describing mouth versus leg versus hand motions activate different parts of pre-motor cortex (as well as other areas, specifically BA 6, BA 40, and BA 44). From a broader perspective, to the extent that evidence is found indicating that imagery plays a role in language understanding, this bolsters an embodied view of meaning, in which the particular experiences a language user has had in their life, in their body, create the substantive basis for language production and understanding, as suggested by a number of authors, like Barsalou (1999), Zwaan (1999), Glenberg and Robertson (2000), Bergen, et al. (2003), Feldman and Narayanan (2004), Bergen and Chang (2005), and Matlock (To Appear), and MacWhinney (In Press). While important and productive lines of research are beginning to gain momentum in the area of mental simulation and language understanding, there has been insufficient focus thus far on the exact linguistic mechanisms that trigger mental simulation. More specifically, there are two questions that have yet to be addressed in previous studies. The first concerns the types of language that trigger simulation and the second concerns the degree of detail involved in simulation. It is of critical theoretical importance to determine how prevalent language-triggered motor simulation is – whether it occurs only when people process language about Processing sentences describing actions performed by the hearer (e.g. You gave Andy a pizza) primes actually performing a motor action compatible with the one described (Glenberg & Kaschak 2002), This result has been interpreted as indicating that processing meaning involves the activation of motor control circuitry to prepare the language understander for situated action. A complementary view (Bergen & Chang 2005) argues that motor control structures are automatically and unconsciously engaged during motion language processing irrespective of whether that language pertains to the understander, because the meaning of action language is inherently grounded in motor control circuitry. To distinguish between these views, we must determine whether motor activity results from processing language about actions performed by and on third persons (e.g. Andy gave Sara a pizza.) Two experiments tested the scope of compatible action facilitation during sentence understanding, where sentences either encoded motion in a particular direction (e.g. John opened the drawer) or using a particular handshape (e.g. Mary grabbed the marble.) Both studies yielded significant Action-sentence Compatibility Effects, demonstrating that whether language is about the understander or not, it engages their motor system. Keywords: sentence processing, mental simulation, motor control, Action-sentence Compatibility Effect Introduction Language use integrally involves perceptual and motor processes, since the production of language requires the control of facial, manual, and other effectors, and language processing begins with the detection of visual, auditory, and other perceptual cues. However, language appears to engage perceptual and motor systems and the neural structures dedicated to them in another, less obvious way. Just as performing imagery about action (Porro et al. 1996, Lotze et al. 1999) and perception (Kosslyn et al. 2001) makes use of action and perception systems, so it now appears that processing language about perceptual or motor content results in the activation of neural structures overlapping with those that would be used to actually perceive or perform the described content. The mental (re)creation of perceptual and motor experiences (among others) in order to deeply understand language goes under the rubric of mental simulation (Barsalou 1999). The notion that language understanding makes significant use of perception and action imagery has been proposed in a variety of contexts (Barsalou 1999, Zwaan 1999, Glenberg & Robertson 2000, Feldman & Narayanan 2004, Gallese & Lakoff 2005, Bergen & Chang 2005). What these various views share is the idea that language understanding entails

Exploring virtual environments with an EEG-based BCI through motor imagery.

Abstract: In this paper, we describe the possibility of navigating in a virtual environment using the output signal of an EEG-based Brain-Computer Interface (BCI). The graphical capabilities of virtual reality (VR) should help to create new BCI-paradigms and improve feedback presentation. The objective of this combination is to enhance the subject's learning process of gaining control of the BCI. In this study, the participant had to imagine left or right hand movements while exploring a virtual conference room. By imaging a left hand movement the subject turned virtually to the left inside the room and with right hand imagery to the right. In fact, three trained subjects reached 80% to 100% BCI classification accuracy in the course of the experimental sessions. All subjects were able to achieve a rotation in the VR to the left or right by approximately 45 degrees during one trial.

Influence of environmental context on motor imagery quality: an autonomic nervous system study

Abstract: This study was devised to evaluate the effect of the environmental information context on mental representation of a complex motor skill. Regional and national table tennis players were asked to perform a forehand topspin shot after an experimenter had served; during imagery sessions, they had to represent mentally the same sequence: 1) neutral imagery was conducted without information provided by reference to table-tennis, 2) context imagery included influences of the appropriate environmental context, wearing sports clothes, handling the table tennis paddle, hearing ball rebounds. Results evidenced that subjects had greater difficulty in building up a mental representation of the sequence in a neutral environment than with context imagery: longer and higher neurovegetative responses, closer to those recorded during actual movement, were observed in the context imagery modality than in the neutral imagery modality. Environmental context in which mental imagery of movement is performed could thus facilitate a subject's ability to build up mental simulation of a motor act. (Biol.Sport 22:215-226, 2005)

Phase Synchrony Rate for the Recognition of Motor Imagery in Brain-Computer Interface

Abstract: Motor imagery attenuates EEG µ and β rhythms over sensorimotor cortices. These amplitude changes are most successfully captured by the method of Common Spatial Patterns (CSP) and widely used in brain-computer interfaces (BCI). BCI methods based on amplitude information, however, have not incoporated the rich phase dynamics in the EEG rhythm. This study reports on a BCI method based on phase synchrony rate (SR). SR, computed from binarized phase locking value, describes the number of discrete synchronization events within a window. Statistical nonparametric tests show that SRs contain significant differences between 2 types of motor imageries. Classifiers trained on SRs consistently demonstrate satisfactory results for all 5 subjects. It is further observed that, for 3 subjects, phase is more discriminative than amplitude in the first 1.5-2.0 s, which suggests that phase has the potential to boost the information transfer rate in BCIs.

Effect of a fatiguing protocol on motor imagery accuracy.

Abstract: This study was devised to evaluate the influence of muscle fatigue on athletes' ability to perform motor imagery. Performance impairment is a consequence of fatigue, but alterations on perception and mental activity may also occur. To test whether peripheral fatigue affects mental processes, ten sports students imagined three consecutive countermovement jumps before and after a fatiguing protocol, through repetition of upright movements, at 70% of maximal voluntary contraction, until exhaustion. Autonomic nervous system responses and imagined movement durations were considered the dependent variables. Actual duration was systematically overestimated during both visual and kinesthetic imagery, but motor imagery duration and autonomic responses were similar without and under fatigue. Results suggest that muscle fatigue, unlike fatigue induced by prolonged exercise, does not elicit mental fatigue and therefore does not alter motor imagery accuracy.

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

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

VR-mirror : A virtual reality system for mental practice in post-stroke rehabilitation

Abstract: Developments in basic neurological research and techniques used to train professional athletes suggest that one way of facilitating this learning process of motor schemas is through the use of motor imagery, a training technique in which the procedure required to perform a task is mentally rehearsed in absence of actual physical movement. Clinical studies have shown that rehabilitation of hemiplegic and hemiparetic patients can be improved by integrating physical and mental practice. In this paper, we describe an advanced virtual reality workbench, the VR- Mirror, that it has been designed to support stroke patients with upper-limb hemiplegia in generating motor images. The development of this prototype has been supported by the Commission of the European Communities (CEC) - IST programme (Project I-Learning, 1ST 2001-38861).

Assessing recovery in middle cerebral artery stroke using functional MRI

Abstract: Primary objective: To understand the temporal evolution of brain reorganization during recovery from stroke. Research design: A patient who suffered left middle cerebral artery stroke 9 months earlier was studied on three occasions, ∼1 month apart. Methods and procedures: Brain activation was studied using functional Magnetic Resonance Imaging (fMRI). During each session, the patient performed a finger-to-thumb opposition task, which involved one bimanual and two unimanual conditions. Each condition consisted of overt movement of fingers and imagery of the same task. Results: With recovery, greater recruitment was observed of the affected primary motor cortex (M1) and a decrease in activation of the unaffected M1 and supplementary motor area. In addition, the widespread activation of brain areas seen during the initial session changed to a more focused pattern of activation as the patient recovered. Imagery tasks resulted in similar brain activity as overt execution pointing to imagery as a potential tool...

The movement-specific effect of motor imagery on the premotor time.

Abstract: The purpose of this study was to investigate the effect of motor imagery on the premotor time (PMT). Twelve healthy adults performed reaction time movements in response to external visual signals at rest, when holding an object (muscle activation), or performing different background imagined movements (motor imagery). When compared to rest, muscle activation reduced the PMT; imagined finger extension of the right hand and imagined finger flexion of the left hand elongated the PMT; imagined finger flexion of the right hand had no effect on the PMT. This movement-specific effect is interpreted as the sum of the excitatory effect caused by enhanced corticospinal excitability specifically for the primary mover of the imagined movement and an overall inhibition associated with increased task complexity during motor imagery. Our results clearly demonstrate that motor imagery has movement-specific effects on the PMT.