Showing papers on "Motor imagery published in 2000"

Close interrelation of motor development and cognitive development and of the cerebellum and prefrontal cortex.

Abstract: Motor development and cognitive development may be fundamentally interrelated. Contrary to popular notions that motor development begins and ends early, whereas cognitive development begins and ends later, both motor and cognitive development display equally protracted developmental timetables. When cognitive development is perturbed, as in a neurodevelopmental disorder, motor development is often adversely affected. While it has long been known that the striatum functions as part of a circuit with dorsolateral prefrontal cortex, it is suggested here that the same is true for the cerebellum and that the cerebellum may be important for cognitive as well as motor functions. Like prefrontal cortex, the cerebellum reaches maturity late. Many cognitive tasks that require prefrontal cortex also require the cerebellum. To make these points, evidence is summarized of the close co-activation of the neocerebellum and dorsolateral prefrontal cortex in functional neuroimaging, of similarities in the cognitive sequelae of damage to dorsolateral prefrontal cortex and the neocerebellum, of motor deficits in "cognitive" developmental disorders, and of abnormalities in the cerebellum and in prefrontal cortex in the same developmental disorders.

Mu and beta rhythm topographies during motor imagery and actual movements.

Abstract: People can learn to control the 8-12 Hz mu rhythm and/or the 18-25 Hz beta rhythm in the EEG recorded over sensorimotor cortex and use it to control a cursor on a video screen. Subjects often report using motor imagery to control cursor movement, particularly early in training. We compared in untrained subjects the EEG topographies associated with actual hand movement to those associated with imagined hand movement. Sixty-four EEG channels were recorded while each of 33 adults moved left- or right-hand or imagined doing so. Frequency-specific differences between movement or imagery and rest, and between right- and left-hand movement or imagery, were evaluated by scalp topographies of voltage and r spectra, and principal component analysis. Both movement and imagery were associated with mu and beta rhythm desynchronization. The mu topographies showed bilateral foci of desynchronization over sensorimotor cortices, while the beta topographies showed peak desynchronization over the vertex. Both mu and beta rhythm left/right differences showed bilateral central foci that were stronger on the right side. The independence of mu and beta rhythms was demonstrated by differences for movement and imagery for the subjects as a group and by principal components analysis. The results indicated that the effects of imagery were not simply an attenuated version of the effects of movement. They supply evidence that motor imagery could play an important role in EEG-based communication, and suggest that mu and beta rhythms might provide independent control signals.

Real-time EEG analysis with subject-specific spatial patterns for a brain-computer interface (BCI)

Abstract: Electroencephalogram (EEG) recordings during right and left motor imagery allow one to establish a new communication channel for, e.g., patients with amyotrophic lateral sclerosis. Such an EEG-based brain-computer interface (BCI) can be used to develop a simple binary response for the control of a device. Three subjects participated in a series of on-line sessions to test if it is possible to use common spatial patterns to analyze EEG in real time in order to give feedback to the subjects. Furthermore, the classification accuracy that can be achieved after only three days of training was investigated. The patterns are estimated from a set of multichannel EEG data by the method of common spatial patterns and reflect the specific activation of cortical areas. By construction, common spatial patterns weight each electrode according to its importance to the discrimination task and suppress noise in individual channels by using correlations between neighboring electrodes. Experiments with three subjects resulted in an error rate of 2, 6 and 14% during on-line discrimination of left- and right-hand motor imagery after three days of training and make common spatial patterns a promising method for an EEG-based brain-computer interface.

EEG-based communication: a pattern recognition approach

Abstract: Presents an overview of the authors' research into brain-computer interfacing (BCI). This comprises an offline study of the effect of motor imagery on EEG and an online study that uses pattern classifiers incorporating parameter uncertainty and temporal information to discriminate between different cognitive tasks in real-time.

Transcranial Magnetic Stimulation of Primary Motor Cortex Affects Mental Rotation

Abstract: Neuroimaging studies have shown that motor structures are activated not only during overt motor behavior but also during tasks that require no overt motor behavior, such as motor imagery and mental rotation. We tested the hypothesis that activation of the primary motor cortex is needed for mental rotation by using single- pulse transcranial magnetic stimulation (TMS). Single-pulse TMS was delivered to the representation of the hand in left primary motor cortex while participants performed mental rotation of pictures of hands and feet. Relative to a peripheral magnetic stimulation control condition, response times (RTs) were slower when TMS was delivered at 650 ms but not at 400 ms after stimulus onset. The magnetic stimulation effect at 650 ms was larger for hands than for feet. These findings demonstrate that (i) activation of the left primary motor cortex has a causal role in the mental rotation of pictures of hands; (ii) this role is stimulus-specific because disruption of neural activity in the hand area slowed RTs for pictures of hands more than feet; and (iii) left primary motor cortex is involved relatively late in the mental rotation process.

Imagining the impossible: intact motor representations in hemiplegics.

Abstract: Motor imagery is known to involve brain regions vital to the performance of motor skills including primary motor cortex. The present results show that, following cerebral vascular accidents (CVAs) affecting a variety of these regions, many adults with left or right upper-limb paralysis (i.e. hemiparesis/hemiplegia) retain the ability to accurately represent prehensile movements involving the impaired limb. This suggests that during the acute phase of recovery many CVA patients can use motor imagery to activate partially damaged motor networks; a process that may facilitate functional reorganization. This ability was, however, compromised in cases with right posterior parietal or left frontal lesions. This pattern is consistent with the hypothesis that imagined prehension, like actual reaching and grasping, involves a network of highly interconnected areas distributed throughout parietal and frontal cortices.

Ipsilateral involvement of primary motor cortex during motor imagery.

Abstract: To investigate whether motor imagery involves ipsilateral cortical regions, we studied haemodynamic changes in portions of the motor cortex of 14 right-handed volunteers during actual motor performance (MP) and kinesthetic motor imagery (MI) of simple sequences of unilateral left or right finger movements, using functional magnetic resonance imaging (fMRI). Increases in mean normalized fMRI signal intensities over values obtained during the control (visual imagery) task were found during both MP and MI in the posterior part of the precentral gyrus and supplementary motor area, both on the contralateral and ipsilateral hemispheres. In the left lateral premotor cortex, fMRI signals were increased during imagery of either left or right finger movements. Ipsilateral cortical clusters displaying fMRI signal changes during both MP and MI were identified by correlation analyses in 10 out of 14 subjects; their extent was larger in the left hemisphere. A larger cortical population involved during both contralateral MP and MI was found in all subjects. The overall spatial extent of both the contralateral and the ipsilateral MP + MI clusters was approximately 90% of the whole cortical volume activated during MP. These results suggest that overlapping neural networks in motor and premotor cortex of the contralateral and ipsilateral hemispheres are involved during imagery and execution of simple motor tasks.

Motor imagery in normal subjects and in asymmetrical Parkinson’s disease A PET study

Abstract: Objective: To investigate, using PET and H 2 15 O, brain activation abnormalities of patients with PD during motor imagery. To determine whether motor imagery activation patterns depend on the hand used to complete the task. Background: Previous work in PD has shown that bradykinesia is associated with slowness of motor imagery. Methods: The PET study was performed in eight patients with PD with predominantly right-sided akinesia, and in eight age-matched control subjects, all right-handed. Regional cerebral blood flow was measured by PET and H 2 15 O while subjects imagined a predetermined unimanual externally cued sequential movement with a joystick with either the left or the right hand, and during a rest condition. Results: In normal subjects, the prefrontal cortex, supplementary motor area (SMA), superior parietal lobe, inferior frontal gyrus, and cerebellum were activated during motor imagery with either the left or the right hand. Contralateral primary motor cortex activation was noted only when the task was imagined with the right (dominant) hand, whereas activation of the dorsolateral prefrontal cortex was observed only during imagery with the left hand. In patients with PD, motor imagery with the right (“akinetic”) hand was characterized by lack of activation of the contralateral primary sensorimotor cortex and the cerebellum, persistent activation of the SMA, and bilateral activation of the superior parietal cortex. Motor imagery with the left (“non-akinetic”) hand was also abnormal, with lack of activation of the SMA compared with controls. Conclusions: In patients with PD with predominantly right-sided akinesia, brain activation during motor imagery is abnormal and may appear even with the less affected hand. In normal subjects, brain activation during motor imagery depends on the hand used in the imagined movement.

Spatiotemporal ERD/ERS patterns during voluntary movement and motor imagery.

Abstract: Publisher Summary This chapter discusses the three phases during voluntary, self-paced movements—preparation, execution, and recovery. Each of these phases has its characteristic spatiotemporal ERD/ERS pattern. The preparatory phase is characterized by an onset of mu event-related desynchronization (ERD) prior to voluntary movement with a contralateral preponderance. The central beta desynchronization starts later around one second before movement onset, with a clear contralateral dominance. The Execution of movement is accompanied by a bilateral pattern of mu and central beta desynchronization with a clear focus close to the corresponding cortical representation area. In addition to this ERD, an enhancement of gamma band activity can be found parallel with the motor act. One important feature of this gamma ERS is its cortical topography concomitant with the functional anatomy of the sensorimotor cortex. Embedded in desynchronized mu rhythm are bursts of beta oscillations (post-movement beta ERS) focused to the primary motor area. Beta ERS is of special interest because of its strict somatotopic organization, its good signal (beta ERS)-to-noise (EEG with desynchronized mu rhythm) ratio and its coincidence with a reduced corticospinal excitability. The results on motor imagery can be interpreted such that execution and imagination of movement involve the same cortical network in the corresponding representation area.

The precuneus in motor imagery: a magnetoencephalographic study.

Abstract: Magnetoencephalography was applied to subjects who imagined themselves hurdling in self-centered space. In three of six subjects all 300 trials in the motor imagery condition revealed the precuneus dipole. When we divided the 300 trials into four overlapping blocks (one block = 150 trials), all six subjects showed precuneus activity. The latency of the precuneus dipole was about 220 ms. We suggest that the precuneus activity during motor imagery involves retrieval of spatial information and/or setting up spatial attributes. Only in one subject but twice, the current dipole located in the supplementary motor area was observed 60 ms after activation of the precuneus, which suggests that the signal from the precuneus for motor imagery is transferred to the supplementary motor area.

Motor imagery and visual event recognition.

Abstract: In order to investigate the influence of covert motor processes in the recognition of visual events, we compared the response times (RT) in two similar tasks, one involving a to-be-grasped object and the other involving a to-be-observed object. In one task, we asked right-handed subjects to tell whether an observed screwdriver presented in different orientations and rotating on its main axis was screwing or unscrewing (screwdriver task). In the other task the visual stimuli were precisely the same, but subjects had to think of the screwdriver as being the pivot pin of an imagined clock, turning its hands from the back (clock task). They had to tell whether the imagined clock hands were moving clockwise or counterclockwise. In the screwdriver task, a prominent right-left asymmetry consisting of higher RTs for stimulus orientations awkward for a right-hand grip was present, suggesting that subjects adopted a strategy based upon mentally simulating the grabbing of the screwdriver handle with the dominant hand. Consistent with the hypothesis that the crucial factor that triggers these motor imagery processes is the "graspability" of the relevant object in the scene, in the clock task the right-left asymmetry disappeared in most subjects, RTs mirroring the symmetry of the visual stimuli. These findings indicate that, when interpreting a scene involving a to-be-grasped object, a strategy based upon motor imagery (mental grasping), probably unfolding procedural knowledge, is activated. When the scene involves a to-be-observed object, the recognition task can be accomplished through other, possibly visual, strategies.

Motor imagery in Huntington's disease

Abstract: We investigated the role of the basal ganglia (BG) in motor imagery in patients with Huntington's disease (HD). A visually guided pointing task assessed whether patients could predict actual movement time (MT) through motor imagery. Executed and imagined movements were performed when vision was constrained centrally, or was free to move. Participants completed a series of imagined and actual movements, with and without central fixation, between two target circles. Patients with HD and controls' imagined MTs were significantly faster than their executed MTs. In compliance with Fitt's law, both actual and imagined MTs increased as a function of increasing task difficulty. We conclude that motor imagery is relatively preserved in HD.