Is the human primary motor cortex involved in motor imagery?

Whole-body isometric force/torque measurements for functional assessment in neuro-rehabilitation: platform design, development and verification

BACKGROUND

One of the main scientific and technological challenges of rehabilitation bioengineering is the development of innovative methodologies, based on the use of appropriate technological devices, for an objective assessment of patients undergoing a rehabilitation treatment. Such tools should be as fast and cheap to use as clinical scales, which are currently the daily instruments most widely used in the routine clinical practice.

METHODS

A human-centered approach was used in the design and development of a mechanical structure equipped with eight force/torque sensors that record quantitative data during the initiation of a predefined set of Activities of Daily Living (ADL) tasks, in isometric conditions.

RESULTS

Preliminary results validated the appropriateness, acceptability and functionality of the proposed platform, that has become now a tool used for clinical research in three clinical centres.

CONCLUSION

This paper presented the design and development of an innovative platform for whole-body force and torque measurements on human subjects. The platform has been designed to perform accurate quantitative measurements in isometric conditions with the specific aim to address the needs for functional assessment tests of patients undergoing a rehabilitation treatment as a consequence of a stroke.The versatility of the system also enlightens several other interesting possible areas of application for therapy in neurorehabilitation, for research in basic neuroscience, and more.

An fMRI investigation on image generation in different sensory modalities: the influence of vividness

In the present fMRI study the issue of the specific cortices activation during imagery generation in different sensory modalities is addressed. In particular, we tested whether the vividness variability of imagery was reflected in the BOLD signal within specific sensory cortices. Subjects were asked to generate a mental image for each auditory presented sentence. Each imagery modality was contrasted with an abstract sentence condition. In addition, subjects were asked to fill the Italian version of the Questionnaire Upon Mental Imagery (QMI) prior to each neuroimaging session. In general, greater involvement of sensory specific cortices in high-vivid versus low-vivid subjects was found for visual (occipital), gustatory (anterior insula), kinaesthetic (pre-motor), and tactile and for somatic (post-central parietal) imagery modalities. These results support the hypothesis that vividness is related to image format: high-vivid subjects would create more analogical representations relying on the same specific neural substrates active during perception with respect to low-vivid subjects. Results are also discussed according to the simulation perspective.

Motor imagery influences the execution of repetitive finger opposition movements

Motor imagery (MI) is the ability to imagine performing a movement without executing it. In literature, there have been numerous reports on the influence of MI on motor practice and the beneficial effects of "mental practice" on the physical performance has been suggested to rely to the close temporal association between motor rehearsal and actual performance. In the present study, we aimed to evaluate whether the addition of a period of motor imagery between two motor practice trials could modify movement execution in a repetitive finger opposition motor task performed at maximal speed and whether the effect of motor imagery on motor practice is dependant on the complexity of movement. We observed that the addition of motor imagery to the sole motor practice was able to influence the performance of repetitive finger opposition movements inducing an increase of the velocity of movement greater than that observed with the motor practice alone. Further the addition of motor imagery was able to induce a modification in the motor strategy in terms of duration of the main phases of movements. This was more evident when subjects executed a finger sequential task with respect to a simple finger tapping task. We assume that mental rehearsal facilitates the brain network involved in sensorimotor control, particularly acting on those neural structures involved in the motor program.

Brain activity during visual versus kinesthetic imagery: an fMRI study

Although there is ample evidence that motor imagery activates similar cerebral regions to those solicited during actual movements, it is still unknown whether visual (VI) and kinesthetic imagery (KI) recruit comparable or distinct neural networks. The present study was thus designed to identify, through functional magnetic resonance imaging at 3.0 Tesla in 13 skilled imagers, the cerebral structures implicated in VI and KI. Participants were scanned in a perceptual control condition and while physically executing or focusing during motor imagery on either the visual or kinesthetic components of an explicitly known sequence of finger movements. Subjects' imagery abilities were assessed using well-established psychological, chronometric, and new physiological measures from the autonomic nervous system. Compared with the perceptual condition, physical executing, VI, and KI resulted in overlapping (albeit non-identical) brain activations, including motor-related regions and the inferior and superior parietal lobules. By contrast, a divergent pattern of increased activity was observed when VI and KI were compared directly: VI activated predominantly the occipital regions and the superior parietal lobules, whereas KI yielded more activity in motor-associated structures and the inferior parietal lobule. These results suggest that VI and KI are mediated through separate neural systems, which contribute differently during processes of motor learning and neurological rehabilitation.

MOTOR-EVOKED POTENTIALS FOLLOWING IMAGERY AND LIMB DISUSE

This article investigated whether mental imagery training could reduce the detrimental effects produced by limb disuse. Subjects learned a task requiring fifth finger abduction. Motor-evoked potentials (MEPs) were obtained from the abductor digiti minimi muscle using transcranial magnetic stimulation. The arm was casted and the experimental group then practiced using imagery. After seven days, variable error scores increased. The immobilization treatment decreased MEP scores in both groups, with no difference between groups. It is concluded that limb immobilization produces a decrement in the area of motor cortex dedicated to this muscle as a result of disuse. Imagery failed to ameliorate the disuse-related changes.

Neurofunctional modulation of brain regions by distinct forms of motor cognition and movement features

Extrastriate, parietal, and frontal brain regions are differentially involved in distinct kinds of body movements and motor cognition. Using functional magnetic resonance imaging, we investigated the neural mechanisms underlying the observation and mental imagery of meaningful face and limb movements with or without objects. The supplementary motor area was differentially recruited by the mental imagery of movements while there were differential responses of the extrastriate body area (EBA) during the observation conditions. Contrary to most previous reports, the EBA responded to face movements, albeit to a lesser degree than to limb movements. The medial wall of the intraparietal sulcus and adjacent intraparietal cortex was selectively recruited by the processing of meaningful upper limb movements, irrespective of whether these were object-related or not. Besides reach and grasp movements, the intraparietal sulcus may thus be involved in limb gesture processing, that is, in an important aspect of human social communication. We conclude that subregions of a frontal-parietal network differentially interact during the cognitive processing of body movements according to the specific motor-related task at hand and the particular movement features involved.

Automated classification of fMRI data employing trial-based imagery tasks

Automated interpretation and classification of functional MRI (fMRI) data is an emerging research field that enables the characterization of underlying cognitive processes with minimal human intervention. In this work, we present a method for the automated classification of human thoughts reflected on a trial-based paradigm using fMRI with a significantly shortened data acquisition time (less than one minute). Based on our preliminary experience with various cognitive imagery tasks, six characteristic thoughts were chosen as target tasks for the present work: right-hand motor imagery, left-hand motor imagery, right foot motor imagery, mental calculation, internal speech/word generation, and visual imagery. These six tasks were performed by five healthy volunteers and functional images were obtained using a T(*)(2)-weighted echo planar imaging (EPI) sequence. Feature vectors from activation maps, necessary for the classification of neural activity, were automatically extracted from the regions that were consistently and exclusively activated for a given task during the training process. Extracted feature vectors were classified using the support vector machine (SVM) algorithm. Parameter optimization, using a k-fold cross validation scheme, allowed the successful recognition of the six different categories of administered thought tasks with an accuracy of 74.5% (mean)+/-14.3% (standard deviation) across all five subjects. Our proposed study for the automated classification of fMRI data may be utilized in further investigations to monitor/identify human thought processes and their potential link to hardware/computer control.

Juggling with the brain - thought and action in the human motor system

Empirical findings from various research fields indicate that cognitive and motor processes are far less dissimilar than previously thought. The present chapter takes a neuroscientific perspective and offers evidence for similarities between cognition and action focusing on three key players of the classical motor system: the primary motor cortex, the cerebellum, and the premotor cortex. Briefly, although movement execution is apparently supported in part by the same cerebral resources engaged in cognitive processes, the three brain regions reviewed here are differentially engaged in more or less action-bound cognitive processes.

Imaging the imagination: the trouble with motor imagery

Sports and exercise psychology finds itself in a most unfortunate situation these days. While all other branches of the psychological sciences help themselves freely to the glitzy new toys of modern neuroscience--MRI and PET, mostly--exploring the neural underpinnings of whatever cognitive function they are interested in exploring, the sport sciences are left out of the fun for the simple reason that these imaging instruments preclude motion--the very thing then that is the subject of interest to them. There are several legitimate ways around this problem but the one that seems to be most popular is, I think, not--legitimate, that is. The basic idea, unduly sharpened here, is the following. Neuroimaging studies have shown that imagined and actual motion share the same neural substrates or, alternatively, imagining an action corresponds to a subliminal activation of the same brain areas required for its execution. It follows from this, the arguments runs, that motor imagery can be used as a proxy for real motor performance, et voilà, the sports sciences can go wild with all the snazzy brain imaging tools after all--just like everyone else. This notion is, I believe, misbegotten, a house of cards that threatens to cast a long shadow over the field. The present article, then, is, to be frank, intended to put a machete to this kind of thinking. It does this by exposing this conclusion to be based on an unholy marriage of selective data reporting and gross overgeneralization. The result is a wild goose chase fueled by wishful thinking.

Application to robot control using brain function measurement by near-infrared spectroscopy

In recent years, study of brain computer interface (BCI) is conducted actively and many researches of implementation using electro encephalic gram (EEG) are reported. On the other hand, some realization of BCI based on near-infrared spectroscopy (NIRS) also had been reported. Since a measurement instrument for NIRS is comparatively small-scale and it can perform noninvasive measurements, NIRS is expected as one of useful tool in order to realize versatile BCIs. In this paper, the estimation method is shown the possibility of applications to the ON/OFF control of BCI by NIRS. We measured regional cerebral blood flow during tapping movement of the right hand by NIRS and we propose a method to quantitatively estimate start and end timing of movement by using a neural network.

Motor planning, imagery, and execution in the distributed motor network: a time-course study with functional MRI

Activation of motor-related areas has consistently been found during various motor imagery tasks and is regarded as the central mechanism generating motor imagery. However, the extent to which motor execution and imagery share neural substrates remains controversial. We examined brain activity during preparation for and execution of physical or mental finger tapping. During a functional magnetic resonance imaging at 3 T, 13 healthy volunteers performed an instructed delay finger-tapping task either in a physical mode or mental mode. Number stimuli instructed subjects about a finger-tapping sequence. After an instructed delay period, cue stimuli prompted them either to execute the tapping movement or to imagine it. Two types of planning/preparatory activity common for movement and imagery were found: instruction stimulus-related activity represented widely in multiple motor-related areas and delay period activity in the medial frontal areas. Although brain activity during movement execution and imagery was largely shared in the distributed motor network, imagery-related activity was in general more closely related to instruction-related activity than to the motor execution-related activity. Specifically, activity in the medial superior frontal gyrus, anterior cingulate cortex, precentral sulcus, supramarginal gyrus, fusiform gyrus, and posterolateral cerebellum likely reflects willed generation of virtual motor commands and analysis of virtual sensory signals.

Phase synchrony measurement in motor cortex for classifying single-trial EEG during motor imagery

A motor imagery based brain-computer interface (BCI) translates the subject's motor intention into a control signal. For this BCI system, most algorithms are based on power changes of mu and beta rhythms. In this paper, we employ the measurement of phase synchrony to investigate the activities of the supplementary motor area (SMA) and primary motor area (M1) during left/right hand movement imagery. The single-trial phase locking value (PLV) features were derived from intrinsic large-scale and local-scale phase synchronies between and within SMA and M1. The classification performance suggests that phase synchrony is an additional robust feature for differentiating motor imagery states.

Assessment of brain interactivity in the motor cortex from the concept of functional connectivity and spectral analysis of fMRI data

Functional magnetic resonance imaging (fMRI) was used to assess the contributions of movement preparation and execution of a visuomotor task in a cerebral motor network. The functional connectivity of the voxel time series between brain regions in the frequency space was investigated by performing spectral analysis of fMRI time series. The regional interactivities between the two portions of the supplementary motor area (pre-SMA and SMA-proper) and the primary motor cortex (M1), defined as a seed region, were evaluated. The spectral parameter of coherence was used to describe a correlation structure in the frequency domain between two voxel-based time series and to infer the strength of the functional interaction within our presumed motor network of connections. The results showed meaningful differences of the functional interactions between the two portions of the SMA and the M1 area depending on the task conditions. This approach demonstrated the existence of a functional dissociation between the pre-SMA and SMA-proper subregions. We therefore conclude that spectral analysis is useful for identifying functional interactions of brain regions and might provide a powerful tool to quantify changes in connectivity profiles associated with various components of an experimental task.

Motor representations and practice affect brain systems underlying imagery: an FMRI study of internal imagery in novices and active high jumpers

This study used functional magnetic resonance imaging (fMRI) to investigate differences in brain activity between one group of active high jumpers and one group of high jumping novices (controls) when performing motor imagery of a high jump. It was also investigated how internal imagery training affects neural activity. The results showed that active high jumpers primarily activated motor areas, e.g. pre-motor cortex and cerebellum. Novices activated visual areas, e.g. superior occipital cortex. Imagery training resulted in a reduction of activity in parietal cortex. These results indicate that in order to use an internal perspective during motor imagery of a complex skill, one must have well established motor representations of the skill which then translates into a motor/internal pattern of brain activity. If not, an external perspective will be used and the corresponding brain activation will be a visual/external pattern. Moreover, the findings imply that imagery training reduces the activity in parietal cortex suggesting that imagery is performed more automatic and results in a more efficient motor representation more easily accessed during motor performance.

Motor imagery: a window into the mechanisms and alterations of the motor system

Motor imagery is a widely used paradigm for the study of cognitive aspects of action control, both in the healthy and the pathological brain. In this paper we review how motor imagery research has advanced our knowledge of behavioral and neural aspects of action control, both in healthy subjects and clinical populations. Furthermore, we will illustrate how motor imagery can provide new insights in a poorly understood psychopathological condition: conversion paralysis (CP). We measured behavioral and cerebral responses with functional magnetic resonance imaging (fMRI) in seven CP patients with a lateralized paresis of the arm as they imagined moving the affected or the unaffected hand. Imagined actions were either implicitly induced by the task requirements, or explicitly instructed through verbal instructions. We previously showed that implicitly induced motor imagery of the affected limb leads to larger ventromedial prefrontal responses compared to motor imagery of the unaffected limb. We interpreted this effect in terms of greater self-monitoring of actions during motor imagery of the affected limb. Here, we report new data in support of this interpretation: inducing self-monitoring of actions of both the affected and the unaffected limb (by means of explicitly cued motor imagery) abolishes the activation difference between the affected and the unaffected hand in the ventromedial prefrontal cortex. Our results show that although implicit and explicit motor imagery both entail motor simulations, they differ in terms of the amount of action monitoring they induce. The increased self-monitoring evoked by explicit motor imagery can have profound cerebral consequences in a psychopathological condition.

The suppressive influence of SMA on M1 in motor imagery revealed by fMRI and dynamic causal modeling

Although motor imagery is widely used for motor learning in rehabilitation and sports training, the underlying mechanisms are still poorly understood. Based on fMRI data sets acquired with very high temporal resolution (300 ms) under motor execution and imagery conditions, we utilized Dynamic Causal Modeling (DCM) to determine effective connectivity measures between supplementary motor area (SMA) and primary motor cortex (M1). A set of 28 models was tested in a Bayesian framework and the by-far best-performing model revealed a strong suppressive influence of the motor imagery condition on the forward connection between SMA and M1. Our results clearly indicate that the lack of activation in M1 during motor imagery is caused by suppression from the SMA. These results highlight the importance of the SMA not only for the preparation and execution of intended movements, but also for suppressing movements that are represented in the motor system but not to be performed.

[Contribution of the spectral analysis to the brain connectivity study by fMRI]

AIM

To validate, through functional magnetic resonance imaging (fMRI) from spectral analysis of time series during a visuomotor task, a model of functional connectivity mainly constituted by the pre-supplementary motor area (pre-SMA), the supplementary motor area proper (SMA-proper) and the primary motor cortex (M1).

MATERIALS AND METHODS

The paradigm that was tried out in young subjects (n=5) consisted of a preparation task of motor movement. We firstly proceeded with an estimate in the frequency domain of coherency coefficients and values of phase shift between these three areas. Secondly, the estimated coherency coefficients were integrated to a model of functional connectivity. Two interaction coefficients were calculated, one for the related M1 and pre-SMA regions, the other one for the related M1 and SMA-proper regions.

RESULTS AND CONCLUSION

Our results demonstrate hemodynamic activity that definitely occurred earlier in the pre-SMA area during the preparatory period of the task. In the same way, a more important interaction was found between M1 and pre-SMA areas, which corroborates the assumption of the prevalent role played by these two areas in the case of a preparation task of a motor movement. Thus, this study has allowed highlighting a functional dissociation between the two portions of the SMA.

Corticomotor facilitation associated with observation and imagery of hand actions is impaired in Parkinson's disease

In the present report, we extend our previous observations on corticomotor facilitation associated with covert (action observed or imagined) and overt (action imitated) action execution in old adults (Leonard and Tremblay in Exp Brain Res 117:167-175, 2007) to investigate the impact of Parkinson's disease (PD). Participants consisted of 22 older adults (age range 58-76 years) of whom 11 were medicated patients diagnosed with PD (patient group) and 11 were age-matched healthy controls (healthy group). Corticomotor facilitation was assessed by monitoring the changes in the amplitude of motor evoked potentials (MEP) in muscles of the right hand (first dorsal interosseous: FDI; and abductor digiti minimi: ADM) in response to transcranial magnetic stimulation of the left motor cortex. In each group, corticomotor facilitation was assessed with participants seated in front of a computer screen under four testing conditions: (1) REST: eyes closed and instructions to relax for 10 s, (2) OBS: observe action, (3) IMAG: imagine action and (4) IMIT: imitate action. The action depicted in the video displayed the hand of a male subject cutting a piece of material with scissors. Comparison of variations in MEP amplitude revealed a significant interaction between groups and conditions. In the healthy group, the OBS and IMAG conditions were both associated with significant facilitation in the FDI and ADM, whereas the same conditions failed to produce facilitation in the PD group. In both groups, the IMIT condition produced the largest facilitation in hand muscles. Further planned comparisons revealed a significant difference between groups in the FDI for the OBS condition. From these findings, we conclude that, even when properly medicated, old adults with PD may experience major difficulties in engaging the motor system for covert actions, particularly when asked to observe another person's action. This failure of corticomotor facilitation for covert actions appears to be linked with the deficit in motor activation associated with basal ganglia dysfunction in PD and in line with the difficulty experienced in general by patients "to energize" the motor system in preparation for action.

Cortical activation during motor imagery is reduced in Amyotrophic Lateral Sclerosis

The neural correlates of motor execution in Amyotrophic Lateral Sclerosis (ALS) are challenging to investigate due to muscle weakness. Alternatives to traditional motor execution paradigms are therefore of great interest. This study tested the hypothesis that patients with Amyotrophic Lateral Sclerosis (ALS) would show increased cortical activation during motor imagery compared to healthy controls, as seen in studies of motor execution. Functional MRI was used to measure activation during a block design paradigm contrasting imagery of right hand movements against rest in 16 patients with ALS and 17 age-matched healthy controls. Patients with ALS showed reduced activation during motor imagery in the left inferior parietal lobule, and in the anterior cingulate gyrus and medial pre-frontal cortex. This reduction in cortical activation during motor imagery contrasts with the pattern seen during motor execution. This may represent the disruption of normal motor imagery networks by ALS pathology outside the primary motor cortex.

Differential brain processing of audiovisual sexual stimuli in men: Comparative positron emission tomography study of the initiation and maintenance of penile erection during sexual arousal

The human male psychosexual cycle consists of four phases: excitation, plateau, orgasm, and resolution. Identification of the specific neural substrates of each phase may provide information regarding the brain's pathophysiology of sexual dysfunction. We previously analyzed regional cerebral blood flow (rCBF) with H(2)15O-positron emission tomography (PET) during the excitation phase (initiation of penile erection) induced by audiovisual sexual stimuli (AVSS) and identified activation of the cerebellar vermis, the bilateral extrastriate cortex, and right orbitofrontal cortex, suggesting a role of cognition/emotion in the excitement phase. In the present study, we analyzed rCBF of the same six healthy volunteers during the plateau phase (maintenance of penile erection) induced by AVSS and compared the results with those of the excitation phase. Penile rigidity was monitored in real time with RigiScan Plus during PET scanning. Images were analyzed by statistical parametric mapping (SPM) software, and rCBF in the amygdala, hypothalamus, anterior cingulate, and insula was measured. During the plateau phase, primary subcortical activation was noted in the right ventral putamen, indicating motivational factors in the sexual response via the limbic reward circuit. A significant increase in rCBF in the left hypothalamus was also observed during the plateau phase. The right anterior cingulate and left insula were specifically activated during the excitation phase but not during the plateau phase. These results indicate a significant role of the ventral putamen and the hypothalamus in the plateau phase and confirm that paralimbic and limbic components of the human brain differentially coordinate the sexual response in a psychosexual phase-dependent manner.

The functional role of dorso-lateral premotor cortex during mental rotation

Subjects deciding whether two objects presented at angular disparity are identical or mirror versions of each other usually show response times that linearly increase with the angle between objects. This phenomenon has been termed mental rotation. While there is widespread agreement that parietal cortex plays a dominant role in mental rotation, reports concerning the involvement of motor areas are less consistent. From a theoretical point of view, activation in motor areas suggests that mental rotation relies upon visuo-motor rather than visuo-spatial processing alone. However, the type of information that is processed by motor areas during mental rotation remains unclear. In this study we used event-related fMRI to assess whether activation in parietal and dorsolateral premotor areas (dPM) during mental rotation is distinctively related to processing spatial orientation information. Using a newly developed task paradigm we explicitly separated the processing steps (encoding, mental rotation proper and object matching) required by mental rotation tasks and additionally modulated the amount of spatial orientation information that had to be processed. Our results show that activation in dPM during mental rotation is not strongly modulated by the processing of spatial orientation information, and that activation in dPM areas is strongest during mental rotation proper. The latter finding suggests that dPM is involved in more generalized processes such as visuo-spatial attention and movement anticipation. We propose that solving mental rotation tasks is heavily dependent upon visuo-motor processes and evokes neural processing that may be considered as an implicit simulation of actual object rotation.

Motor imagery and action observation: cognitive tools for rehabilitation

Rehabilitation, for a large part may be seen as a learning process where old skills have to be re-acquired and new ones have to be learned on the basis of practice. Active exercising creates a flow of sensory (afferent) information. It is known that motor recovery and motor learning have many aspects in common. Both are largely based on response-produced sensory information. In the present article it is asked whether active physical exercise is always necessary for creating this sensory flow. Numerous studies have indicated that motor imagery may result in the same plastic changes in the motor system as actual physical practice. Motor imagery is the mental execution of a movement without any overt movement or without any peripheral (muscle) activation. It has been shown that motor imagery leads to the activation of the same brain areas as actual movement. The present article discusses the role that motor imagery may play in neurological rehabilitation. Furthermore, it will be discussed to what extent the observation of a movement performed by another subject may play a similar role in learning. It is concluded that, although the clinical evidence is still meager, the use of motor imagery in neurological rehabilitation may be defended on theoretical grounds and on the basis of the results of experimental studies with healthy subjects.

Amplitude and phase coupling measures for feature extraction in an EEG-based brain-computer interface

Most of the feature extraction methods in existing brain-computer interfaces (BCIs) are based on the dynamic behavior of separate signals, without using the coupling information between different brain regions. In this paper, amplitude and phase coupling measures, quantified by a nonlinear regressive coefficient and phase locking value respectively, were used for feature extraction. The two measures were based on three different coupling methods determined by neurophysiological a priori knowledge, and applied to a small number of electrodes of interest, leading to six feature vectors for classification. Five subjects participated in an online BCI experiment during which they were asked to imagine a movement of either the left or right hand. The electroencephalographic (EEG) recordings from all subjects were analyzed offline. The averaged classification accuracies of the five subjects ranged from 87.4% to 92.9% for the six feature vectors and the best classification accuracies of the six feature vectors ranged between 84.4% and 99.6% for the five subjects. The performance of coupling features was compared with that of the autoregressive (AR) feature. Results indicated that coupling measures are appropriate methods for feature extraction in BCIs. Furthermore, the combination of coupling and AR feature can effectively improve the classification accuracy due to their complementarities.

Motor imagery of complex everyday movements. An fMRI study

The present study aimed to investigate the functional neuroanatomical correlates of motor imagery (MI) of complex everyday movements (also called everyday tasks or functional tasks). 15 participants imagined two different types of everyday movements, movements confined to the upper extremities (UE; e.g., eating a meal) and movements involving the whole body (WB; e.g., swimming), during fMRI scanning. Results showed that both movement types activated the lateral and medial premotor cortices bilaterally, the left parietal cortex, and the right basal ganglia. Direct comparison of WB and UE movements further revealed a homuncular organization in the primary sensorimotor cortices (SMC), with UE movements represented in inferior parts of the SMC and WB movements in superior and medial parts. These results demonstrate that MI of everyday movements drives a cortical network comparable to the one described for more simple movements such as finger opposition. The findings further are in accordance with the suggestion that motor imagery-based mental practice is effective because it activates a comparable cortical network as overt training. Since most people are familiar with everyday movements and therefore a practice of the movement prior to scanning is not necessarily required, the current paradigm seems particularly appealing for clinical research and application focusing on patients with low or no residual motor abilities.

Understanding non-biological dynamics with your own premotor system

The human premotor cortex (PM) appears to subserve a variety of cognitive and motor functions, including the prediction of non-biological dynamics. In the present study we directly tested the correspondence of premotor correlates of predicting different non-biological dynamics and imagining different actions by means of functional magnetic resonance imaging. Prediction tasks on either spatial, object or rhythmic dynamics were expected to draw on premotor areas involved in motor imagery tasks for arm, hand and mouth movements, respectively. Firstly, the results confirmed comparable dorsal-to-ventral distributions of property effects (in prediction) and movement effects (in motor imagery) in PM. Secondly, even more direct correspondences were observed for mouth movement imagery and rhythm prediction in inferior ventral PM and for arm movement imagery and spatial prediction in dorsal PM. Hand movement imagery and object prediction led to activations in closely adjacent areas in left superior ventral PM. Together, the present findings support the notion that to-be-predicted stimulus dynamics and motor effectors are coupled in lateral PM according to a pragmatic default. Beyond that, the results add further support to the notion that the human PM is involved in the prediction of many if not all kinds of dynamics.

Corticomotor facilitation associated with observation, imagery and imitation of hand actions: a comparative study in young and old adults

In the present report, we extent our previous findings (Clark et al. in Neuropsychologia 42:105-122, 2004) on corticomotor facilitation associated with covert (observation and imagery) and overt execution (action imitation) of hand actions to better delineate the selectivity of the effect in the context of an object-oriented action. A second aim was to examine whether the pattern of facilitation would be affected by age. Corticomotor facilitation was determined in two groups of participants (young n = 21, 24 +/- 2 years; old n = 19, 62 +/- 6 years) by monitoring changes in the amplitude and latency of motor evoked potentials (MEPs) elicited in hand muscles by transcranial magnetic stimulation. MEP responses were measured from both the first dorsal interosseous (FDI, task selective muscle) and the abductor digiti minimi (ADM) of the right hand while participants attended to four different video presentations. Each of four videos provided specific instructions for participants to either: (1) close their eyes and relax (REST), (2) observe the action attentively (OBS), (3) close their eyes and mentally simulate the action (IMAG), or (4) imitate the action (IMIT). The action depicted in the videos represented a male subject cutting a piece of material with scissors. In the young group, the pattern of results revealed selective facilitation in the FDI in conditions involving either covert (OBS and IMAG) or overt action execution (IMIT). In the ADM, only overt execution with action imitation was associated with significant MEP facilitation. In the old group, a similar pattern of results was observed, although the modulation was less selective than that seen in the young group. In fact, older individuals often exhibited concomitant facilitation in both the FDI and ADM during either covert (OBS and IMAG conditions) or overt action execution (IMIT condition). Taken together, these results further corroborate the notion that the corticomotor system is selectively active when actions are covertly executed through internal simulation triggered by observation or by motor imagery, as proposed by Jeannerod (Neuroimage 14:S103-S109, 2001). With aging, the ability to produce corticomotor facilitation in association with covert action execution appears to be largely preserved, although there seems to be a loss in selectivity. This lack of selectivity may, in turn, reflect age-related alterations in the function of the corticospinal system, which may impair the ability to individuate finger movements either in the covert or overt stage of action execution.

Cortical correlates of TMS-induced phantom hand movements revealed with concurrent TMS-fMRI

We studied an amputee patient who experiences a conscious sense of movement (SoM) in her phantom hand, without significant activity in remaining muscles, when transcranial magnetic stimulation (TMS) is applied at appropriate intensity over the corresponding sector of contralateral motor cortex. We used the novel methodological combination of TMS during fMRI to reveal the neural correlates of her phantom SoM. A critical contrast concerned trials at intermediate TMS intensities: low enough not to produce overt activity in remaining muscles; but high enough to produce a phantom SoM on approximately half such trials. Comparing trials with versus without a phantom SoM reported phenomenally, for the same intermediate TMS intensities, factored out any non-specific TMS effects on brain activity to reveal neural correlates of the phantom SoM itself. Areas activated included primary motor cortex, dorsal premotor cortex, anterior intraparietal sulcus, and caudal supplementary motor area, regions that are also involved in some hand movement illusions and motor imagery in normals. This adds support to proposals that a conscious sense of movement for the hand can be conveyed by activity within corresponding motor-related cortical structures.

Neural substrates for motor imagery in severe hemiparesis

BACKGROUND

The beneficial effects of imagined movements on motor learning and performance suggest that motor imagery is functionally close to preparatory and executive motor processes.

OBJECTIVE

The purpose of this study was to examine the cortical processes associated with imagery of movement of the wrist in subjects with severe hemiparesis.

METHODS

During fMRI, subjects with stroke performed alternating blocks of imagining wrist-tracking movements with the hemiparetic hand, active wrist-tracking movements with the unaffected hand, and resting. Control subjects performed the same tasks using an assigned hand. Cortical activation in the primary motor (M1), primary sensory (S1), supplementary motor area (SMA), and pre-SMA regions was determined through a laterality index of active voxels and signal intensity. Ability to imagine was assessed with an Imagery Rating Scale.

RESULTS

All subjects displayed primarily contralateral control during the track condition. Healthy subjects demonstrated contralateral control in all areas during the imagine condition, whereas subjects with stroke displayed primarily contralateral activation in S1 but ipsilateral in M1 and SMA. The percentage change in signal intensity was greater in the ipsilateral hemisphere in subjects with stroke than in the ipsilateral hemisphere in healthy subjects during the imagine condition. Additionally, subjects with self-reported low ability to imagine displayed no difference in activation compared to those with high imagery ability.

CONCLUSIONS

These findings are consistent with other works demonstrating primarily ipsilateral control of the hemiparetic hand in subjects with functional movement and lay the groundwork for further investigation into the ability of mental imagery to affect functionally relevant cortical control in subjects recovering from stroke.

No evidence for a substantial involvement of primary motor hand area in handedness judgements: a transcranial magnetic stimulation study

Twelve right-handed volunteers were asked to judge the laterality of a hand stimulus by pressing a button with one of their toes. Judgements were based on two-dimensional drawings of the back or palm of a right or left hand at various orientations. Suprathreshold single-pulse transcranial magnetic stimulation (TMS) was given to the left primary motor hand area (M1-HAND) at 0, 200, 400, 600, 800 or 1000 ms after stimulus onset to probe the functional involvement of the dominant left M1 at various stages of handedness recognition. We found that mean reaction times and error rates increased with angle of rotation depending on the actual biomechanical constraints of the hand but suprathreshold TMS had no influence on task performance regardless of the timing of TMS. However, the excitability of the corticomotor output from the left M1-HAND was modulated during the reaction. Judging left hand drawings was associated with an attenuation of motor-evoked potentials 300-100 ms before the response, whereas judging right hand drawings facilitated the motor-evoked potentials only immediately before the response. These effects were the same for pictures of backs and palms and were independent of the angle of rotation. The failure of TMS to affect task performance suggests that there is no time window during which the M1-HAND makes a critical contribution to mental rotation of the hand. The modulation of motor-evoked potentials according to the laterality of the stimulus indicates a secondary effect of the task on corticomotor excitability that is not directly related to mental rotation itself.

Motor Imagery

Background and Purpose— Understanding brain plasticity after stroke is important in developing rehabilitation strategies. Active movement therapies show considerable promise but depend on motor performance, excluding many otherwise eligible patients. Motor imagery is widely used in sport to improve performance, which raises the possibility of applying it both as a rehabilitation method and to access the motor network independently of recovery. Specifically, whether the primary motor cortex (M1), considered a prime target of poststroke rehabilitation, is involved in motor imagery is unresolved.

Summary of Review— We review methodological considerations when applying motor imagery to healthy subjects and in patients with stroke, which may disrupt the motor imagery network. We then review firstly the motor imagery training literature focusing on upper-limb recovery, and secondly the functional imaging literature in healthy subjects and in patients with stroke.

Conclusions— The review highlights the difficulty in addressing cognitive screening and compliance in motor imagery studies, particularly with regards to patients with stroke. Despite this, the literature suggests the encouraging effect of motor imagery training on motor recovery after stroke. Based on the available literature in healthy volunteers, robust activation of the nonprimary motor structures, but only weak and inconsistent activation of M1, occurs during motor imagery. In patients with stroke, the cortical activation patterns are essentially unexplored as is the underlying mechanism of motor imagery training. Provided appropriate methodology is implemented, motor imagery may provide a valuable tool to access the motor network and improve outcome after stroke.

Limb (hand vs. foot) and response conflict have similar effects on event-related potentials (ERPs) recorded during motor imagery and overt execution

Although there is substantial evidence that motor execution (M-Ex) and motor imagery (M-Im) share a common neural substrate, the role of the primary motor cortex (M1) during imagery is still a matter of debate. The present ERP study tries to clarify the functional similarity between the two processes in respect of (i) the engagement of the corresponding somatotopic M1 areas during execution and imagery of hand vs. foot movements; and (ii) the effect of conflicting information on response preparation. To this end, we recorded ERPs from 28 electrode sites in 19 participants while they performed a conflict task with congruent (target and flanker arrowheads pointing in the same direction) and incongruent (target pointing in the opposite direction to the flanker arrowheads) trials. We obtained the lateralized readiness potential (LRP), a component generated in M1, while subjects physically executed or mentally simulated the task. As expected by the somatotopic organization of M1, the LRP was of opposite polarity when foot, rather than hand, movements were prepared. The inversion of polarity also occurred during M-Im, a result that strongly argues in favour of the participation of M1 in motor imagery. In incongruent trials, longer LRP latencies, a premature preparation of the incorrect response (positive deflection in LRP waveform) and a fronto-central N2 component associated with response conflict appeared during both M-Ex and M-Im. Altogether, the results support the functional equivalence of the two processes and give support to the clinical use of M-Im for the improvement and recovery of motor functions.

Motor memory consolidation in sleep shapes more effective neuronal representations

Learning a motor skill involves a latent process of consolidation that develops after training to enhance the skill in the absence of any practice and crucially depends on sleep. Here, we show that this latent consolidation during sleep changes the brain representation of the motor skill by reducing overall the neocortical contributions to the representation. Functional magnetic resonance brain imaging was performed during initial training and 48 h later, at retesting, on a sequential finger movement task with training followed by either a night of regular sleep or sleep deprivation. An additional night of sleep for all subjects served to rule out unspecific effects of sleep loss at retrieval testing. Posttraining sleep, but not sleep deprivation, led to improved motor skill performance at retrieval. This sleep-dependent improvement was linked to greatly reduced brain activation in prefrontal, premotor, and primary motor cortical areas, along with a stronger involvement of left parietal cortical regions. Our findings indicate that storing a motor skill during sleep reorganizes its brain representation toward enhanced efficacy.

The selection of intended actions and the observation of others' actions: A time-resolved fMRI study

Whenever we plan, imagine, or observe an action, the motor systems that would be involved in preparing and executing that action are similarly engaged. The way in which such common motor activation is formed, however, is likely to differ depending on whether it arises from our own intentional selection of action or from the observation of another's action. In this study, we use time-resolved event-related functional MRI to tease apart neural processes specifically related to the processing of observed actions, the selection of our own intended actions, the preparation for movement, and motor response execution. Participants observed a finger gesture movement or a cue indicating they should select their own finger gesture to perform, followed by a 5-s delay period; participants then performed the observed or self-selected action. During the preparation and readiness for action, prior to initiation, we found activation in a common network of higher motor areas, including dorsal and ventral premotor areas and the pre-supplementary motor area (pre-SMA); the more caudal SMA showed greater activation during movement execution. Importantly, the route to this common motor activation differed depending on whether participants freely selected the actions to perform or whether they observed the actions performed by another person. Observation of action specifically involved activation of inferior and superior parietal regions, reflecting involvement of the dorsal visual pathway in visuomotor processing required for planning the action. In contrast, the selection of action specifically involved the dorsal lateral prefrontal and anterior cingulate cortex, reflecting the role of these prefrontal areas in attentional selection and guiding the selection of responses.

Lateral Somatotopic Organization During Imagined and Prepared Movements

Motor imagery is a complex cognitive operation that requires memory retrieval, spatial attention, and possibly computations that are analogs of the physical movements being imagined. Likewise, motor preparation may or may not involve computations that are analogs of actual movements. To test whether motor imagery or motor preparation activate representations that are specific to the body part whose movement is imagined or prepared, participants performed, imagined, and prepared hand movements while undergoing functional MRI scanning. Actual hand movements activated components of the motor system including primary motor and somatosensory cortex, the supplementary motor area, the thalamus, and the cerebellum. All of these areas showed strong lateral organization, such that moving a given hand activated the contralateral cortex and ipsilateral cerebellum most strongly. During motor imagery and motor preparation, activity throughout the motor system was much reduced relative to overt movement. However, significant lateral organization was observed during both motor imagery and motor preparation in primary motor cortex, the supplementary motor area, and the thalamus. These results support the view that the subjective experience of imagined movement is accompanied by computations that are analogs of the physical movement that is imagined. They also suggest that in this regard motor imagery and motor preparation are similar.

Estimation of optimal location of EEG reference electrode for motor imagery based BCI using fMRI

Brain computer interface (BCI) is based on brain activity from voluntary will, and controls a computer system through only the imagination or other mental activity. In order to improve the performance of the BCI system based on the scalp EEG, it is important to determine suitable locations for the EEG electrodes according to brain activity as well as the location of reference electrode of the EEG, while most of conventional studies do not much consider about the location of the reference electrode. In this paper, we estimate the proper reference electrode location of the BCI system whose mental tasks are left and right finger movement imagination. The suggested location of the reference electrode is obtained by analyzing the fMRI imaging results. Further online EEG experiment confirmed that choosing supplementary motor area (SMA) as the reference is effective in enhancing the performance of the BCI system.

The neural basis of narrative imagery: emotion and action

It has been proposed that narrative emotional imagery activates an associative network of stimulus, semantic, and response (procedural) information. In previous research, predicted response components have been demonstrated through psychophysiological methods in peripheral nervous system. Here we investigate central nervous system concomitants of pleasant, neutral, and unpleasant narrative imagery with functional magnetic resonance imaging. Subjects were presented with brief narrative scripts over headphones, and then imagined themselves engaged in the described events. During script perception, auditory association cortex showed enhanced activation during affectively arousing (pleasant and unpleasant), relative to neutral imagery. Structures involved in language processing (left middle frontal gyrus) and spatial navigation (retrosplenium) were also active during script presentation. At the onset of narrative imagery, supplementary motor area, lateral cerebellum, and left inferior frontal gyrus were initiated, showing enhanced signal change during affectively arousing (pleasant and unpleasant), relative to neutral scripts. These data are consistent with a bioinformational model of emotion that considers response mobilization as the measurable output of narrative imagery.

Imagery of motor actions: Differential effects of kinesthetic and visual–motor mode of imagery in single-trial EEG

Single-trial motor imagery classification is an integral part of a number of brain-computer interface (BCI) systems. The possible significance of the kind of imagery, involving rather kinesthetic or visual representations of actions, was addressed using the following experimental conditions: kinesthetic motor imagery (MIK), visual-motor imagery (MIV), motor execution (ME) and observation of movement (OOM). Based on multi-channel EEG recordings in 14 right-handed participants, we applied a learning classifier, the distinction sensitive learning vector quantization (DSLVQ) to identify relevant features (i.e., frequency bands, electrode sites) for recognition of the respective mental states. For ME and OOM, the overall classification accuracies were about 80%. The rates obtained for MIK (67%) were better than the results of MIV (56%). Moreover, the focus of activity during kinesthetic imagery was found close to the sensorimotor hand area, whereas visual-motor imagery did not reveal a clear spatial pattern. Consequently, to improve motor-imagery-based BCI control, user training should emphasize kinesthetic experiences instead of visual representations of actions.

Paradoxical lateralization of brain potentials during imagined foot movements

Though each foot is controlled primarily by the contralateral hemisphere, the event-related brain potentials preceding an overt foot movement are largest over the ipsilateral side of the head. Because such "paradoxical lateralization" results from the spatial organization of the motor homunculus, it can provide a sign of motor-cortex activation. We report paradoxical lateralization in the potentials accompanying imagined foot movements, thereby demonstrating a contribution of cortical areas directly involved in movement execution.

Premovement activity of the pre-supplementary motor area and the readiness for action: Studies of time-resolved event-related functional MRI

The supplementary motor area (SMA) is thought to play in important role in the preparation and organisation of voluntary movement. It has long been known that cortical activity begins to increase up to 2s prior to voluntary self-initiated movement. This increasing premovement activity measured in EEG is known as the Bereitschaftspotential or readiness potential. Modern functional brain imaging methods, using event-related and time-resolved functional MRI techniques, are beginning to reveal the role of the SMA, and in particular the more anterior pre-SMA, in premovement activity associated with the readiness for action. In this paper we review recent studies using event-related time-resolved fMRI methods to examine the time-course of activation changes within the SMA throughout the preparation, readiness and execution of action. These studies suggest that the pre-SMA plays a common role in encoding or representing actions prior to our own voluntary self-initiated movements, during motor imagery, and from the observation of others' actions. We suggest that the pre-SMA generates and encodes motor representations which are then maintained in readiness for action.

Covert speech arrest induced by rTMS over both motor and nonmotor left hemisphere frontal sites

Blocking the capacity to speak aloud (overt speech arrest, SA) may be induced by repetitive transcranial magnetic stimulation (rTMS). The possibility, however, of blocking internal speech (covert SA) has not been explored. To investigate this issue, we conducted two rTMS experiments. In the first experiment, we stimulated two left frontal lobe sites. The first was a motor site (left posterior site) and the second was a nonmotor site located in correspondence to the posterior part of the inferior frontal gyrus (IFG) (left anterior site). The corresponding right hemisphere nonmotor SA site was stimulated as a control. In the second experiment, we focused on the right hemisphere and stimulated a right hemisphere motor site (right posterior site), and, as control sites, a right hemisphere nonmotor site corresponding to the IFG (right anterior site) and a left hemisphere anteromedial site (left control). For both experiments, participants performed a syllable counting task both covertly and overtly for each stimulation site. Longer latencies in this task imply the occurrence of an overt and/or covert SA. All participants showed significantly longer latencies when stimulation was either over the left posterior or the left anterior site, as compared with the right hemisphere site (Experiment 1). This result was observed for the overt and covert speech task alike. During stimulation of the posterior right hemisphere site, a dissociation for overt and covert speech was observed. An overt SA was observed but there was no evidence for a covert SA (Experiment 2). Taken together, the results show that rTMS can induce a covert SA when applied to areas over the brain that are pertinent to language. Furthermore, both the left posterior/motor site and the left anterior/IFG site appear to be essential to language elaboration even when motor output is not required.

Kinesthetic, but not visual, motor imagery modulates corticomotor excitability

The hypothesis that motor imagery and actual movement involve overlapping neural structures in the central nervous system is supported by multiple lines of evidence. The aim of this study was to examine the modulation of corticomotor excitability during two types of strategies for motor imagery: Kinesthetic Motor Imagery (KMI) and Visual Motor Imagery (VMI) in a phasic thumb movement task. Transcranial magnetic stimulation (TMS) was applied over the contralateral motor cortex (M1) to elicit motor evoked potentials (MEPs) in the dominant abductor pollicis brevis (APB) and abductor digiti minimi (ADM). In a separate experiment, transcutaneous electrical stimuli were delivered to the median nerve at the dominant wrist, to elicit F-waves from APB. Imagined task performance was paced with a 1 Hz auditory metronome, and stimuli were delivered either 50 ms before (ON phase), or 450 ms after (OFF phase), the metronome beeps. Recordings were also made during two control conditions: Rest, and a Visual Static Imagery (VSI) condition. Significant MEP amplitude facilitation occurred only in APB, and only during the ON phase of KMI. F-wave persistence and amplitude were unaffected by imagery. These results demonstrate that kinesthetic, but not visual, motor imagery modulates corticomotor excitability, primarily at the supraspinal level. These findings have implications for the definition of motor imagery, and for its therapeutic applications.