Showing papers on "Motor imagery published in 2004"
TL;DR: The emulation theory of representation is developed and explored as a framework that can revealingly synthesize a wide variety of representational functions of the brain, including reasoning, theory of mind phenomena, and language.
Abstract: The emulation theory of representation is developed and explored as a framework that can revealingly synthesize a wide vari- ety of representational functions of the brain. The framework is based on constructs from control theory (forward models) and signal processing (Kalman filters). The idea is that in addition to simply engaging with the body and environment, the brain constructs neural circuits that act as models of the body and environment. During overt sensorimotor engagement, these models are driven by efference copies in parallel with the body and environment, in order to provide expectations of the sensory feedback, and to enhance and process sensory information. These models can also be run off-line in order to produce imagery, estimate outcomes of different actions, and eval- uate and develop motor plans. The framework is initially developed within the context of motor control, where it has been shown that inner models running in parallel with the body can reduce the effects of feedback delay problems. The same mechanisms can account for motor imagery as the off-line driving of the emulator via efference copies. The framework is extended to account for visual imagery as the off-line driving of an emulator of the motor-visual loop. I also show how such systems can provide for amodal spatial imagery. Per- ception, including visual perception, results from such models being used to form expectations of, and to interpret, sensory input. I close by briefly outlining other cognitive functions that might also be synthesized within this framework, including reasoning, theory of mind phenomena, and language.
1,031 citations
01 Jan 2004
TL;DR: The emulation theory of representation as mentioned in this paper is a framework that can reveally synthesize a wide variety of representational functions of the brain, including reasoning, theory of mind phenomena, and language.
Abstract: The emulation theory of representation is developed and explored as a framework that can revealingly synthesize a wide variety of representational functions of the brain. The framework is based on constructs from control theory (forward models) and signal processing (Kalman filters). The idea is that in addition to simply engaging with the body and environment, the brain constructs neural circuits that act as models of the body and environment. During overt sensorimotor engagement, these models are driven by efference copies in parallel with the body and environment, in order to provide expectations of the sensory feedback, and to enhance and process sensory information. These models can also be run off-line in order to produce imagery, estimate outcomes of different actions, and evaluate and develop motor plans. The framework is initially developed within the context of motor control, where it has been shown that inner models running in parallel with the body can reduce the effects of feedback delay problems. The same mechanisms can account for motor imagery as the off-line driving of the emulator via efference copies. The framework is extended to account for visual imagery as the off-line driving of air emulator of the motor-visual loop. I also show how such systems can provide for amodal spatial imagery. Perception, including visual perception, results from such models being used to form expectations of, and to interpret, sensory input. I close by briefly outlining other cognitive functions that might also be synthesized within this framework, including reasoning, theory of mind phenomena, and language.
955 citations
TL;DR: The results suggest that networks underlying these behaviors are not identical, despite the extensive overlap between E and KI, and highlights the role of the connection of superior parietal lobule to the supplementary motor area in both types of motor imagery.
Abstract: Motor imagery, the 'mental rehearsal of motor acts without overt movements', involves either a visual representation (visual imagery, VI) or mental simulation of movement, associated with a kinesthetic feeling (kinetic imagery, KI). Previous brain imaging work suggests that patterns of brain activation differ when comparing execution (E) with either type of imagery but the functional connectivity of the participating networks has not been studied. Using functional magnetic resonance imaging (fMRI) and structural equation modeling, this study elucidates the inter-relationships among the relevant areas for each of the three motor behaviors. Our results suggest that networks underlying these behaviors are not identical, despite the extensive overlap between E and KI. Inputs to M1, which are facilitatory during E, have the opposite effect during KI, suggesting a physiological mechanism whereby the system prevents overt movements. Finally, this study highlights the role of the connection of superior parietal lobule to the supplementary motor area in both types of motor imagery.
506 citations
14 Jun 2004
TL;DR: An asynchronous BCI is characterized by continuous analyzing and classification of EEG data, and it is important to maximize the hits during an intended mental task and to minimize the false positive detections in the resting or idling state.
Abstract: Nearly all electroencephalogram (EEG)-based brain-computer interface (BCI) systems operate in a cue-paced or synchronous mode. This means that the onset of mental activity (thought) is externally-paced and the EEG has to be analyzed in predefined time windows. In the near future, BCI systems that allow the user to intend a specific mental pattern whenever she/he wishes to produce such patterns will also become important. An asynchronous BCI is characterized by continuous analyzing and classification of EEG data. Therefore, it is important to maximize the hits (true positive rate) during an intended mental task and to minimize the false positive detections in the resting or idling state. EEG data recorded during right/left motor imagery is used to simulate an asynchronous BCI. To optimize the classification results, a refractory period and a dwell time are introduced.
267 citations
TL;DR: In this article, the authors investigated the cortical network which mediates music performance compared to music imagery in 12 music academy students playing the right hand part of a Bartok piece using functional magnetic resonance imaging (fMRI).
262 citations
TL;DR: The present promising results suggest that the source analysis approach could manifest a clearer picture on the cortical activity, and thus facilitate the classification of MI tasks from scalp EEGs.
Abstract: We report a pilot study of performing classification of motor imagery for brain–computer interface applications, by means of source analysis of scalp-recorded EEGs. Independent component analysis (ICA) was used as a spatio-temporal filter extracting signal components relevant to left or right motor imagery (MI) tasks. Source analysis methods including equivalent dipole analysis and cortical current density imaging were applied to reconstruct equivalent neural sources corresponding to MI, and classification was performed based on the inverse solutions. The classification was considered correct if the equivalent source was found over the motor cortex in the corresponding hemisphere. A classification rate of about 80% was achieved in the human subject studied using both the equivalent dipole analysis and the cortical current density imaging analysis. The present promising results suggest that the source analysis approach could manifest a clearer picture on the cortical activity, and thus facilitate the classification of MI tasks from scalp EEGs.
235 citations
01 Aug 2004
TL;DR: A novel finding of a transient response reflecting the onset of imagination which does not lead to sustained M1 activation may explain previous contradictory reports.
Abstract: Participation of the primary motor cortex (M1) in motor imagery was addressed using functional magnetic resonance imaging at 2.0 T and 2 x 2 x 4 mm3 resolution in six right-handed subjects. Paradigms comprised visually cued execution and imagination of a sequential finger-to-thumb opposition task (12 s) contrasted with motor rest and visual imagery (18 s), respectively. Motor execution activated M1 as well as other parts of the motor system including supplementary motor area (SMA) and premotor areas (PM). In contrast, motor imagery did not lead to activations in M1 except for 1/6 subjects but involved SMA and PM bilaterally as well as the anterior intraparietal cortex. Moreover, a region-of-interest analysis revealed a weak initial MRI signal increase in M1 in 4/6 subjects. This novel finding of a transient response reflecting the onset of imagination which does not lead to sustained M1 activation may explain previous contradictory reports.
227 citations
TL;DR: Motor imagery training without supervision at home may improve performance on the trained task only, and the relation between movement imagery, attention and perceived personal control over recovery remained unclear.
Abstract: Objective: To assess the efficacy of motor imagery training for arm function in chronic stroke patients. The relation between mental processes such as attentional and perceived personal control over recovery, and motor imagery was additionally investigated.Design and subjects: Twenty patients with long-term motor impairments (mean two years post stroke), were assessed before and after four weeks of training. Ten patients mentally rehearsed movements with their affected arm. Their recovery was compared with patients who performed nonmotor imagery (n =5), or who were not engaged in mental rehearsal (n =5).Setting: Patients were recruited from the stroke database of Ninewells Hospital, Dundee. Assessment and training were performed at the patients' home.Interventions: The motor imagery group was asked to practise daily imagining moving tokens with their affected arm. The nonmotor imagery group rehearsed visual imagery of previously seen pictures. All patients practised physically moving the tokens.Main measu...
223 citations
TL;DR: The present method promises to provide a useful alternative as a general purpose classification procedure for MI classification by using time-frequency synthesis approach to accommodate the individual difference, and using the spatial patterns derived from electroencephalogram (EEG) rhythmic components as the feature description.
218 citations
TL;DR: Loss of a single limb per se does not prevent motor imagery but it significantly enhances its difficulty; these subjects apparently perform the hand recognition task using a strategy in which they initially mentally simulate movements of their dominant limb, consistent with the view that only 'tools' can be incorporated in a dynamic body schema.
Abstract: Previous research suggests a close similarity in brain activity between mental simulation of a movement and its real counterpart. To explore this similarity, we aimed to assess whether imagery is affected by the loss of a limb or of its motor skills. We examined the performance of 16 adult, upper limb amputees (and age-matched controls) in a left/right hand judgement task that implicitly requires motor imagery. The experimental group included subjects who had suffered the amputation of the dominant or the non-dominant limb. Although responding well above chance, amputees as a group were slower and less accurate than controls. Nevertheless, their response pattern was similar to that of controls, namely slower response times and more errors for stimuli depicting hands in unnatural orientations, i.e. postures difficult to reach with a real movement. Interestingly, for all stimuli, amputees' performance was strongly affected by the side of limb loss: subjects who underwent amputation of their preferred limb made more errors and required greater latencies to respond as compared with amputees of the non-dominant limb. In a further analysis we observed that the habit of wearing an aesthetic prosthesis significantly interfered with the ability to judge the corresponding hand. Our data lead to three main conclusions: (i) loss of a single limb per se does not prevent motor imagery but it significantly enhances its difficulty; (ii) these subjects apparently perform the hand recognition task using a strategy in which they initially mentally simulate movements of their dominant limb; (iii) wearing a prosthesis, devoid of any motor function, seems to interfere with motor imagery, consistent with the view that only 'tools' can be incorporated in a dynamic body schema.
212 citations
TL;DR: The similarity found between observation and imagery of hand actions in terms of corticospinal facilitation is interpreted in the light of the motor-simulation theory of Jeannerod, which proposes that perceiving actions involves neural simulation of the same action by the observer, thereby explaining the parallel between actions observed and actions imaged at the representational level.
TL;DR: In this paper, the primary motor cortex (M1) in motor imagery was addressed using functional magnetic resonance imaging at 2.0 T and 2 x 2 x 4 mm3 resolution in six right-handed subjects.
TL;DR: Results indicate that the actual limb posture affects the process of motor imagery, and postural modulation effect is discussed, which induced a higher increase in corticospinal excitability, when compared with PB.
Abstract: In order to study the interaction between proprioceptive information and motor imagery, we herein investigate how compatible and incompatible postural signals influence corticospinal excitability during the mental simulation of hand movements. Subjects were asked to imagine themselves joining the tips of the thumb and the little finger while they maintained one of the two following hand postures: posture A (PA, compatible), little finger, index and thumb extended, the remaining fingers flexed; or posture B (PB, incompatible), index and thumb extended, other fingers flexed. All subjects rated the imagined finger opposition movements as easier to perform when the hand was kept in PA than in PB (P < 0.01) and the correlation between the duration of motor imagery and movement execution was also higher for PA than PB (P < 0.01). For each posture, motor evoked potentials (MEPs) elicited by focal transcranial magnetic stimulation (TMS) of the left motor cortex were recorded from the right opponens pollicis muscle during both motor imagery (MI) and rest (R) conditions. MEP area varied according to the hand posture: PA induced a higher increase in corticospinal excitability, when compared with PB. These results indicate that the actual limb posture affects the process of motor imagery. The source of this postural modulation effect is discussed.
TL;DR: It was suggested that children with DCD, unlike controls, do not automatically enlist motor imagery when performing mental rotation, but rely on an alternative object-based strategy that preserves speed and accuracy.
Abstract: Recent studies show that children with developmental coordination disorder (DCD) have difficulties in generating an accurate visuospatial representation of an intended action, which are shown by deficits in motor imagery. This study sought to test this hypothesis further using a mental rotation paradigm. It was predicted that children with DCD would not conform to the typical pattern of responding when required to imagine movement of their limbs. Participants included 16 children with DCD and 18 control children; mean age for the DCD group was 10 years 4 months, and for controls 10 years. The task required children to judge the handedness of single-hand images that were presented at angles between 0° and 180° at 45° intervals in either direction. Results were broadly consistent with the hypothesis above. Responses of the control children conformed to the typical pattern of mental rotation: a moderate trade-off between response time and angle of rotation. The response pattern for the DCD group was less typical, with a small trade-off function. Response accuracy did not differ between groups. It was suggested that children with DCD, unlike controls, do not automatically enlist motor imagery when performing mental rotation, but rely on an alternative object-based strategy that preserves speed and accuracy. This occurs because these children manifest a reduced ability to make imagined transformations from an egocentric or first-person perspective.
TL;DR: In this article, Malouin et al. examined the relationship between working memory and motor improvement obtained after a single training session combining mental and physical practice, and found that the motor improvement was measured by the percentage change in limb loading on the affected limb after training and 24 hours later (follow-up).
TL;DR: It will be outlined how conceptual spaces can represent various kind of information and how they can be used to describe concept learning.
Abstract: I focus on the distinction between sensation and perception. Perceptions contain additional information that is useful for interpreting sensations. Following Grush, I propose that emulators can be seen as containing (or creating) hidden variables that generate perceptions from sensations. Such hidden variables could be used to explain further cognitive phenomena, for example, causal reasoning.
TL;DR: Performance time showed a high correlation between real and virtual movements in the following conditions: during dominant and non-dominant hand movements; in simple and complex motor tasks; in normal volunteers and patients suffering unilateral brain damage caused by a stroke.
15 Mar 2004
TL;DR: The main aim was to evaluate which two of several candidate tasks lead to patterns of electroencephalographic (EEG) activity that could be differentiated most reliably and, therefore, produce the highest communication rate.
Abstract: Different cognitive tasks were investigated for use with a brain-computer interface (BCI). The main aim was to evaluate which two of several candidate tasks lead to patterns of electroencephalographic (EEG) activity that could be differentiated most reliably and, therefore, produce the highest communication rate. An optimal signal processing method was also sought to enhance differentiation of EEG profiles across tasks. In ten normal subjects (five male), aged 29-54 years, EEG activity was recorded from four channels during cognitive tasks grouped in pairs, and performed alternately. Four imagery tasks were: spatial navigation around a familiar environment; auditory imagery of a familiar tune; and right and left motor imagery of opening and closing the hand. Signal processing methodology included autoregressive (AR) modeling and classification based on logistic regression and a nonlinear generative classifier. The highest communication rate was found using the navigation and auditory imagery tasks. In terms of classification performance and, hence, possible communication rate, these results were significantly better (p<0.05) than those obtained with the classical pairing of motor tasks involving imaginary movements of the left and right hands. In terms of EEG data analysis, a nonlinear classification model provided more robust results than a linear model (p/spl Lt/0.01), and a lower AR model order than those used in previous work was found to be effective. These findings have implications for establishing appropriate methods to operate BCI systems, particularly for disabled people who may experience difficulty with motor tasks, even motor imagery.
TL;DR: The efficacy of MP for activating cerebral and cerebellar sensorimotor networks suggests that MP might be an effective substitute or complement to PP to activate compensatory networks for motor rehabilitation.
Abstract: Motor behavior and sensorimotor activation of the cerebrum and cerebellum were measured before and after motor imagery-based mental practice (MP) and physical practice (PP) of a sequential motor task. Two-button-press sequences (A, B) were performed outside a magnetic resonance imaging scanner and at 2 Hz inside the scanner during a pretest. Participants (n = 39) completed PP, MP, or no practice (NP) of Sequence A for 1 week and were posttested. Sequence A performance improved 121%, 86%, and 4% for the PP, MP, and NP groups, respectively (p 0.05). PP improvements were accompanied by increased striatal and decreased cerebellar activation, while MP improvements were accompanied by increased cerebellar, premotor, and striatal activation. The efficacy of MP for activating cerebral and cerebellar sensorimotor networks suggests that MP might be an effective substitute or complement to PP to activate compensatory networks for motor rehabilitation.
TL;DR: Preliminary evidence that internally simulating movements may induce functional reorganization of the contralesional hand representation of a chronic, densely hemiplegic, cerebral vascular accident (CVA) patient is discussed.
TL;DR: The specific facilitatory effect of motor imagery, action/object observation, and speech listening on motor excitability shown by these experiments provides strong evidence that the motor system is constantly involved whenever the idea of an action is evoked.
Abstract: We continuously act on objects, on other individuals, and on ourselves, and actions represent the only way we have to manifest our own desires and goals. In the last two decades, electrophysiological experiments have demonstrated that actions are stored in the brain according to a goal-related organization. The authors review a series of experimental data showing that this "vocabulary of motor schemata" could also be used for non-strictly motor purposes. In the first section, they present data from monkey experiments describing the functional properties of inferior premotor cortex and, in more detail, the properties of visuomotor neurons responding to objects and others' actions observation (mirror neurons). In the second section, human data are reviewed, with particular regard to electrophysiological experiments aiming to investigate how action representations are stored and addressed. The specific facilitatory effect of motor imagery, action/object observation, and speech listening on motor excitability shown by these experiments provides strong evidence that the motor system is constantly involved whenever the idea of an action is evoked.
TL;DR: This review examines the role of the posterior parietal cortex (PPC) in schizophrenia within the context of recent models of self-monitoring deficits in patients with schizophrenia and suggests that patients experiencing passivity phenomena may have particular impairments of parietal function related to poor utilisation of forward models of intended actions.
TL;DR: The general principles of ideomotor theory are described and recent empirical work that supports this theory is reviewed, including studies on the role of response effects for the selection and initiation of simple actions and for learning and performing action sequences.
Abstract: Ideomotor approaches to motor control focus on the cognitive mechanisms underlying voluntary action selection. Ideomotor theory states that actions are cognitively represented in terms of their anticipated sensory consequences (response effects) and that there are bidirectional associations between movements and ensuing response effects. Accordingly, the anticipation of response effects may serve as a mental cue to activate the corresponding movement. The aim of the present paper is to describe the general principles of ideomotor theory and to review recent empirical work that supports this theory. Specifically, we describe studies on the role of response effects for the selection and initiation of simple actions and for learning and performing action sequences. Finally, we discuss potential implications of these results for sport psychology, in particular with reference to the role of motor imagery in mental practice.
TL;DR: Results showed first that the difference between actual and mental motor acts takes place at the late stage of the preparation period and consists of a quantitative modulation of the activity of common structures in M1, and showed that primary motor structures are involved to the same extent in the actual or imagined execution of a motor act.
Abstract: Studies evaluating the role of the executive motor system in motor imagery came to a general agreement in favour of the activation of the primary motor area (M1) during imagery, although in reduced proportion as compared to motor execution. It is still unclear whether this difference occurs within the preparation period or the execution period of the movement, or both. In the present study, EEG was used to investigate separately the preparation and the execution periods of overt and covert movements in adults. We designed a paradigm that randomly mixed actual and kinaesthetic imagined trials of an externally paced sequence of finger key presses. Sixty channel event-related potentials were recorded to capture the cerebral activations underlying the preparation for motor execution and motor imagery, as well as cerebral activations implied in motor execution and motor imagery. Classical waveform analysis was combined with data-driven spatiotemporal segmentation analysis. In addition, a LAURA source localization algorithm was applied to functionally define brain related motor areas. Our results showed first that the difference between actual and mental motor acts takes place at the late stage of the preparation period and consists of a quantitative modulation of the activity of common structures in M1. Second, they showed that primary motor structures are involved to the same extent in the actual or imagined execution of a motor act. These findings reinforce and refine the functional equivalence hypothesis between actual and imagined motor acts.
TL;DR: Transcranial magnetic stimulation was employed to probe the modulatory effects of transcranial direct current stimulation of motor cortex on motor evoked responses (MEPs) produced during motor imagery and no changes in MEP amplitude were found after anodal stimulation.
Abstract: Transcranial magnetic stimulation (TMS) was employed to probe the modulatory effects of transcranial direct current stimulation of motor cortex on motor evoked responses (MEPs) produced during motor imagery. MEP amplitudes at rest and during motor imagery were assessed before and for a period of 60 min after transcranial direct current stimulation (tDCS) applied over the primary motor cortex at 1 mA for 5 min. Cathodal stimulation induced a decrease of about 30% of MEP amplitude at rest and a 50% reduction of MEP size during imagery. Ten minutes after tDCS, MEPs at rest returned to baseline values while MEPs during motor imagery were suppressed for up to 30 min. No changes in MEP amplitude during imagery were found after anodal stimulation. tDCS could represent a powerful tool to modulate the excitability of motor areas involved in mental practice and motor imagery.
TL;DR: The results provide direct evidence of the neural origin of the main phenomena of finger interaction, as well as the involvement of similar neural structures (including M1) during voluntary movement.
01 Jan 2004
TL;DR: An electroencephalogram-based brain-computer interface (BCI) is combined with virtual reality technology to explore the feasibility of walking through a virtual city by using motor imagery.
Abstract: This paper gives a short overview of the feasibility of walking through a virtual city by using motor imagery. Therefore an electroencephalogram-based brain-computer interface (BCI) is combined with virtual reality technology. A BCI transforms bioelectrical brain signals, modulated by mental activity (e.g. imagination of foot or right hand movements), into a control signal. This signal is used to walk forward / backward or to remain stationary inside a virtual city. Results of the first experimental sessions are presented.
TL;DR: A clinical protocol in which interactive tools are used to stimulate motor imagery in hemiplegic stroke patients, thereby helping them to recover lost motor function and improving the cost-effectiveness of training is described.
Abstract: Converging lines of evidence suggest that motor imagery (the mental simulation of a motor act within working memory) is associated with subliminal activation of the motor system. This observation has led to the hypothesis that cortical activation during motor imagery may affect the acquisition of specific motor skills and help the recovery of motor function. In this paper, we describe a clinical protocol in which we use interactive tools to stimulate motor imagery in hemiplegic stroke patients, thereby helping them to recover lost motor function. The protocol consists of an inpatient and an outpatient phase, combining physical and mental practice. In the inpatient phase, patients are trained in a laboratory setting, using a custom-made interactive workbench (VR Mirror). After discharge, patients use a portable device to guide mental and physical practice in a home setting. The proposed strategy is based on the hypotheses that: (a) combined physical and mental practice can make a cost-effective contributio...
TL;DR: These results provide support at the single-neuron level for the role of the medial frontal cortex in the temporal organization and planning of movements in humans.
Abstract: Object The supplementary motor area (SMA) is considered critical in the planning, initiation, and execution of motor acts. Despite decades of research, including electrical stimulation mapping in patients undergoing neurosurgery, the contribution of this region to the generation of motor behavior has remained enigmatic. This is a study of single-neuron responses at various stages of a motor task during depth electrode recording in the SMA, pre-SMA, and medial temporal lobe of humans, with the goal of elucidating the disparate roles of neurons in these regions during movements. Methods The patients were undergoing evaluation for epilepsy surgery requiring implantation of intracranial depth electrodes. Single-unit recordings were made during both the execution and mental imagery of finger apposition sequences. Only medial frontal neurons responded selectively to specific features of the motor plan, such as which hand performed the motor activity or the complexity of the sequence. Neuron activity progressive...
[...]
TL;DR: In this article, a general framework of motor simulation is proposed as a coherent explanation for the various types of action representation during motor imagery, motor decisions, and action observation, which is also used for interpreting the effects of mental training, learning by observation, and the use of neuroprosthetic devices in motorically handicapped people.
Abstract: This paper considers the nature of representations that precede the execution of an action. An analysis of the content of these representations is proposed by using classical tools of cognitive psychology, like introspection and mental chronometry. Their neural vehicle is described in normal subjects with neuroimaging methods and by clinical neuroscience methods like transcranial magnetic stimulation. The contribution of pathological conditions, such as paralysis and amputation, to the description of action representation is discussed. A general framework of motor simulation is proposed as a coherent explanation for the various types of action representation during motor imagery, motor decisions, and action observation. This framework is also used for interpreting the effects of mental training, learning by observation, and the use of neuroprosthetic devices in motorically handicapped people.