Selective activation of a parietofrontal circuit during implicitly imagined prehension

Preserved grip selection planning in chronic unilateral upper extremity amputees

Upper limb amputees receive no proprioceptive or visual sensory feedback about their absent hand. In this study, we asked whether chronic amputees nevertheless retain the ability to accurately plan gripping movements. Fourteen patients and matched controls performed two grip selection tasks: overt grip selection (OGS), in which they used their intact hand to grasp an object that appeared in different orientations using the most natural (under- or overhand) precision grip, and prospective grip selection (PGS), in which they selected the most natural grip for either hand without moving. We evaluated planning accuracy by comparing concordance between grip preferences expressed in PGS vs. OGS for the intact hand and PGS vs. the inverse of OGS responses for the affected hand. Overall, amputees showed no deficits in the accuracy of grip selection planning based on either hand and a consistent preference for less awkward hand postures. We found no evidence for a speed-accuracy tradeoff. Furthermore, selection accuracy did not depend on phantom mobility, phantom limb pain, time since amputation, or the residual limb's shoulder posture. Our findings demonstrate that unilateral upper limb amputees retain the ability to plan movements based on the biomechanics of their affected hand even many years after limb loss. This unimpaired representation may stem from persistent higher-level activity-independent internal representations or may be sustained by sensory feedback from the intact hand.

Motor imagery evokes increased somatosensory activity in Parkinson's disease patients with tremor

Parkinson's disease (PD) is surprisingly heterogeneous: some patients have a prominent resting tremor, while others never develop this symptom. Here we investigate whether the functional organization of the voluntary motor system differs between PD patients with and without resting tremor, and whether these differences relate to the cerebral circuit producing tremor. We compared 18 PD patients with marked tremor, 20 PD patients without tremor, and 19 healthy controls. Subjects performed a controlled motor imagery task during fMRI scanning. We quantified imagery-related cerebral activity by contrasting imagery of biomechanically difficult and easy movements. Tremor-related activity was identified by relating cerebral activity to fluctuations in tremor amplitude, using electromyography during scanning. PD patients with tremor had better behavioral performance than PD patients without tremor. Furthermore, tremulous PD patients showed increased imagery-related activity in somatosensory area 3a, as compared with both healthy controls and to nontremor PD patients. This effect was independent from tremor-related activity, which was localized to the motor cortex, cerebellum, and thalamic ventral intermediate nucleus (VIM). The VIM, with known projections to area 3a, was unique in showing both tremor- and imagery-related responses. We conclude that parkinsonian tremor influences motor imagery by modulating central somatosensory processing through the VIM. This mechanism may explain clinical differences between PD patients with and without tremor.

Motor planning is facilitated by adopting an action's goal posture: an fMRI study

Motor planning is a hierarchical process that is typically organized around an action's goal (e.g., drinking from a cup). However, the motor plan depends not only on the goal but also on the current body state. Here, we investigated how one's own body posture interacts with planning of goal-directed actions. Participants engaged in a grasp selection (GS) task while we manipulated their arm posture. They had to indicate how they would grasp a bar when transporting it from a start to goal position and orientation. We compared situations in which one's body posture was in-congruent with the start posture and/or goal posture of the planned movement. Behavioral results show that GS took longer when one's own body state was incongruent with the goal posture of the planned movement. Correspondingly, neural activity in the intraparietal sulcus (IPS) and extrastriate body area (EBA) was modulated by congruency between the body state and the action plan. IPS was sensitive to overall congruency between body posture and action plan, while the EBA was sensitive specifically to goal posture congruency. Together, our results suggest that IPS maintains an internal state of one's own body posture, while EBA contains a representation of the goal posture of the action plan.

Handedness-dependent and -independent cerebral asymmetries in the anterior intraparietal sulcus and ventral premotor cortex during grasp planning

When planning grasping actions, right-handers show left-lateralized responses in the anterior intraparietal sulcus (aIPS) and ventral premotor cortex (vPMC), two areas that are also implicated in sensorimotor control of grasp. We investigated whether a similar cerebral asymmetry is evident in strongly left-handed individuals. Fourteen participants were trained to grasp an object appearing in a variety of orientations with their left and right hands and with a novel mechanical tool (operated with either hand). BOLD fMRI data were then acquired while they decided prospectively whether an over- or under-hand grip would be most comfortable for grasping the same stimulus set while remaining still. Behavioral performances were equivalent to those recorded previously in right-handers and indicated reliance on effector-specific internal representations. In left-handers, however, grip selection decisions for both sides (left, right) and effectors (hand, tool) were associated with bilateral increases in activity within aIPS and vPMC. A direct comparison between left- and right-handers did reveal equivalent increases in left vPMC regardless of hand dominance. By contrast, aIPS and right vPMC activity were dependent on handedness, showing greater activity in the motor-dominant hemisphere. Though showing bilateral increases in both left- and right-handers, greater increases in the motor dominant hemisphere were also detected in the caudal IPS (cIPS), superior parietal lobule (SPL) and dorsal premotor cortex (dPMC). These findings provide further evidence that regions involved in the sensorimotor control of grasp also participate in grasp planning, and that for certain areas hand dominance is a predictor of the cerebral organization of motor cognitive functions.

Evidence for context sensitivity of grasp representations in human parietal and premotor cortices

Grasp-related responses in neurons of the macaque rostral inferior parietal lobule [PF/PFG and the anterior intraparietal area (AIP)] are modulated by task context. Event-related functional MRI was used to determine whether this is true in putative homologs of the human cortex, the rostral inferior parietal lobule (rIPL) and the anterior intraparietal sulcus (aIPS). Fifteen healthy, right-handed adults were required to select prospectively the most comfortable way to grasp a horizontally oriented handle using the cued hand (left or right). In the "no-rotation" condition, the task was simply to grasp the handle, whereas in the "rotation" condition, the goal was to plan to grasp and rotate it into a vertical orientation with the cued end (medial or lateral) pointing downward. In both conditions, participants remained still and indicated their grip preferences by pressing foot pedals. As in overt grasping, participants' grip preferences were significantly influenced by anticipation of the demands associated with handle rotation. Activity within the aIPS and rIPL increased bilaterally in both the rotation and no-rotation conditions. Importantly, these responses were significantly greater in the rotation vs. no-rotation condition. Similar context effects were detected in the presupplementary motor area, caudal intraparietal sulcus/superior parietal lobule, and bilateral dorsal and left ventral premotor cortices. Grasp representations within the rIPL and aIPS are sensitive to predicted task demands and play a role in context-sensitive grip selection. Moreover, the findings provide additional evidence that areas involved in the sensorimotor control of grasp also contribute to feedforward planning.

Observational learning of new movement sequences is reflected in fronto-parietal coherence

Mankind is unique in her ability for observational learning, i.e. the transmission of acquired knowledge and behavioral repertoire through observation of others' actions. In the present study we used electrophysiological measures to investigate brain mechanisms of observational learning. Analysis investigated the possible functional coupling between occipital (alpha) and motor (mu) rhythms operating in the 10 Hz frequency range for translating "seeing" into "doing". Subjects observed movement sequences consisting of six consecutive left or right hand button presses directed at one of two target-buttons for subsequent imitation. Each movement sequence was presented four times, intervened by short pause intervals for sequence rehearsal. During a control task subjects observed the same movement sequences without a requirement for subsequent reproduction. Although both alpha and mu rhythms desynchronized during the imitation task relative to the control task, modulations in alpha and mu power were found to be largely independent from each other over time, arguing against a functional coupling of alpha and mu generators during observational learning. This independence was furthermore reflected in the absence of coherence between occipital and motor electrodes overlaying alpha and mu generators. Instead, coherence analysis revealed a pair of symmetric fronto-parietal networks, one over the left and one over the right hemisphere, reflecting stronger coherence during observation of movements than during pauses. Individual differences in fronto-parietal coherence were furthermore found to predict imitation accuracy. The properties of these networks, i.e. their fronto-parietal distribution, their ipsilateral organization and their sensitivity to the observation of movements, match closely with the known properties of the mirror neuron system (MNS) as studied in the macaque brain. These results indicate a functional dissociation between higher order areas for observational learning (i.e. parts of the MNS as reflected in 10 Hz coherence measures) and peripheral structures (i.e. lateral occipital gyrus for alpha; central sulcus for mu) that provide low-level support for observation and motor imagery of action sequences.

Use of mental practice to improve upper-limb recovery after stroke: a systematic review

OBJECTIVE

We sought to determine whether mental practice is an effective intervention to improve upper-limb recovery after stroke.

METHOD

We conducted a systematic review of the literature, searching electronic databases for the years 1985 to February 2009. We selected studies according to specified criteria, rated each study for level of evidence, and summarized study elements.

RESULTS

Studies differed with respect to design, patient characteristics, intervention protocols, and outcome measures. All studies used imagery of tasks involving movement of the impaired limb. The length of the interventions and number of practice hours varied. Results suggest that mental practice combined with physical practice improves upper-limb recovery.

CONCLUSION

When added to physical practice, mental practice is an effective intervention. However, generalizations are difficult to make. Further research is warranted to determine who will benefit from training, the dosing needed, the most effective protocols, whether improvements are retained, and whether mental practice affects perceived occupational performance.

Human anterior intraparietal and ventral premotor cortices support representations of grasping with the hand or a novel tool

Humans display a remarkable capacity to use tools instead of their biological effectors. Yet, little is known about the mechanisms that support these behaviors. Here, participants learned to grasp objects, appearing in a variety of orientations, with a novel, handheld mechanical tool. Following training, psychophysical functions relating grip preferences (i.e., pronated vs. supinated) to stimulus orientations indicate a reliance on distinct, effector-specific internal representations when planning grasping actions on the basis of the tool versus the hands. Accompanying fMRI data show that grip planning in both hand and tool conditions was associated with similar increases in activity within the same regions of the anterior intraparietal and caudal ventral premotor cortices, a putative homologue of the macaque anterior intraparietal-ventral premotor (area F5) "grasp circuit." These findings suggest that tool use is supported by effector-specific representations of grasping with the tool that are functionally independent of previously existing representations of the hand and yet occur within the same parieto-frontal regions involved in manual prehension. These levels of representation are critical for accurate planning and execution of actions in a manner that is sensitive to the respective properties of these effectors. These effector-specific representations likely coexist with effector-independent representations. The latter were recently reported in macaque F5 [Umiltà, M. A., Escola, L., Intskirveli, I., Grammont, F., Rochat, M., Caruana, F., et al. When pliers become fingers in the monkey motor system. Proceedings of the National Academy of Sciences, U.S.A., 105, 2209-2213, 2008] and appear to be established by tool use training through modification of existing representations of grasping with the hand. These more abstract levels of representation may facilitate the transfer of skills between hand and tool.

Compromised motor planning and Motor Imagery in right Hemiparetic Cerebral Palsy

We investigated whether motor planning problems in people with Hemiparetic Cerebral Palsy (HCP) are paralleled by impaired ability to use Motor Imagery (MI). While some studies have shown that individuals with HCP can solve a mental rotation task, it was not clear if they used MI or Visual Imagery (VI). In the present study, motor planning and MI were examined in individuals with right HCP (n=10) and controls. Motor planning was measured using an object manipulation task, where participants had to anticipate the end of the motor action. MI was measured using a mental rotation paradigm, where participants judged laterality of hands presented from a back view and a palm view. To test if participants used MI or VI we compared reaction times of lateral versus medial rotations, under the assumption that MI is subject to biomechanical constraints of rotated hands, but VI is not. Individuals with HCP had a higher proportion of task failures due to inappropriate grip choice, exemplifying impaired planning. Second, individuals with HCP did not show a reaction time difference between lateral and medial rotations, indicating an impaired ability to use MI. These findings show that compromised motor planning in HCP is paralleled by an impairment in the ability to use MI. Training of MI may be a useful entry-point for rehabilitation of motor planning problems.

Visual and kinesthetic locomotor imagery training integrated with auditory step rhythm for walking performance of patients with chronic stroke

OBJECTIVE

To compare the effect of visual and kinesthetic locomotor imagery training on walking performance and to determine the clinical feasibility of incorporating auditory step rhythm into the training.

DESIGN

Randomized crossover trial.

SETTING

Laboratory of a Department of Physical Therapy.

SUBJECTS

Fifteen subjects with post-stroke hemiparesis.

INTERVENTION

Four locomotor imagery trainings on walking performance: visual locomotor imagery training, kinesthetic locomotor imagery training, visual locomotor imagery training with auditory step rhythm and kinesthetic locomotor imagery training with auditory step rhythm.

MAIN OUTCOME MEASURES

The timed up-and-go test and electromyographic and kinematic analyses of the affected lower limb during one gait cycle.

RESULTS

After the interventions, significant differences were found in the timed up-and-go test results between the visual locomotor imagery training (25.69 ± 16.16 to 23.97 ± 14.30) and the kinesthetic locomotor imagery training with auditory step rhythm (22.68 ± 12.35 to 15.77 ± 8.58) (P < 0.05). During the swing and stance phases, the kinesthetic locomotor imagery training exhibited significantly increased activation in a greater number of muscles and increased angular displacement of the knee and ankle joints compared with the visual locomotor imagery training, and these effects were more prominent when auditory step rhythm was integrated into each form of locomotor imagery training. The activation of the hamstring during the swing phase and the gastrocnemius during the stance phase, as well as kinematic data of the knee joint, were significantly different for posttest values between the visual locomotor imagery training and the kinesthetic locomotor imagery training with auditory step rhythm (P < 0.05).

CONCLUSIONS

The therapeutic effect may be further enhanced in the kinesthetic locomotor imagery training than in the visual locomotor imagery training. The auditory step rhythm together with the locomotor imagery training produces a greater positive effect in improving the walking performance of patients with post-stroke hemiparesis.

Neural Dissociations between Action Verb Understanding and Motor Imagery

According to embodied theories of language, people understand a verb like throw, at least in part, by mentally simulating throwing. This implicit simulation is often assumed to be similar or identical to motor imagery. Here we used fMRI to test whether implicit simulations of actions during language understanding involve the same cortical motor regions as explicit motor imagery. Healthy participants were presented with verbs related to hand actions (e.g., to throw) and nonmanual actions (e.g., to kneel). They either read these verbs (lexical decision task) or actively imagined performing the actions named by the verbs (imagery task). Primary motor cortex showed effector-specific activation during imagery, but not during lexical decision. Parts of premotor cortex distinguished manual from nonmanual actions during both lexical decision and imagery, but there was no overlap or correlation between regions activated during the two tasks. These dissociations suggest that implicit simulation and explicit imagery cued by action verbs may involve different types of motor representations and that the construct of “mental simulation” should be distinguished from “mental imagery” in embodied theories of language.

Coordination deficits in ideomotor apraxia during visually targeted reaching reflect impaired visuomotor transformations

Ideomotor limb apraxia, commonly defined as a disorder of skilled, purposeful movement, is characterized by spatiotemporal deficits during a variety of actions. These deficits have been attributed to damage to, or impaired retrieval of, stored representations of learned actions, especially object-related movements. However, such deficits might also arise from impaired visuomotor transformation mechanisms that operate in parallel to or downstream from mechanisms for storage of action representations. These transformation processes convert extrinsic visual information into intrinsic neural commands appropriate for the desired motion. These processes are a key part of the movement planning process and performance errors due to inadequate transformations have been shown to increase with the dynamic complexity of the movement. This hypothesis predicts that apraxic patients should show planning deficits when reaching to visual targets, especially when the coordination and/or dynamic requirements of the task increase. Three groups (18 healthy controls, 9 non-apraxic and 9 apraxic left hemisphere damaged patients) performed reaching movements to visual targets that varied in the degree of interjoint coordination required. Relative to the other two groups, apraxic patients made larger initial direction errors and showed higher variability during their movements, especially when reaching to the target with the highest intersegmental coordination requirement. These problems were associated with poor coordination of shoulder and elbow torques early in the movement, consistent with poor movement planning. These findings suggest that the requirement to transform extrinsic visual information into intrinsic motor commands impedes the ability to accurately plan a visually targeted movement in ideomotor limb apraxia.

Brain oscillatory activity during motor imagery in EEG-fMRI coregistration

The purpose of the present work was to investigate the correlation between topographical changes in brain oscillatory activity and the blood oxygenation level-dependent (BOLD) signal during a motor imagery (MI) task using electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) coregistration. EEG was recorded in 7 healthy subjects inside a 1.5 T MR scanner during the imagination of the kinesthetic experience of movement. A Fast Fourier Transform was applied to EEG signal in the rest and active conditions. We used the event-related-synchronization (ERS)/desynchronization (ERD) approach to characterize where the imagination of movement produces a decrease in alpha and beta power. The mean alpha map showed ERD decrease localized over the contralateral sensory motor area (SM1c) and a light desynchronization in the ipsilateral sensory motor area (SM1i); whereas the mean beta map showed ERD decrease over the supplementary motor area (SMA). fMRI showed significant activation in SMA, SM1c, SM1i. The correlation is negative in the contralateral side and positive in the ipsilateral side. Using combined EEG-fMRI signals we obtained useful new information on the description of the changes in oscillatory activity in alpha and beta bands during MI and on the investigation of the sites of BOLD activity as possible sources in generating these rhythms. By correlating BOLD and ERD/ERS we may identify more accurately which regions contribute to changes of the electrical response.

Neural correlates of pantomiming familiar and unfamiliar tools: action semantics versus mechanical problem solving?

This study aims to reveal the neural correlates of planning and executing tool use pantomimes and explores the brain's response to pantomiming the use of unfamiliar tools. Sixteen right-handed volunteers planned and executed pantomimes of equally graspable familiar and unfamiliar tools while undergoing fMRI. During the planning of these pantomimes, we found bilateral temporo-occipital and predominantly left hemispheric frontal and parietal activation. The execution of the pantomimes produced additional activation in frontal and sensorimotor regions. In the left posterior parietal region both familiar and unfamiliar tool pantomimes elicit peak activity in the anterior portion of the lateral bank of the intraparietal sulcus--A region associated with the representation of action goals. The cerebral activation during these pantomimes is remarkably similar for familiar and unfamiliar tools, and direct comparisons revealed only few differences. First, the left cuneus is significantly active during the planning of pantomimes of unfamiliar tools, reflecting increased visual processing of the novel objects. Second, executing (but not planning) familiar tool pantomimes showed significant activation on the convex portion of the inferior parietal lobule, a region believed to serve as a repository for skilled object-related gestures. Given the striking similarity in brain activation while pantomiming familiar and unfamiliar tools, we argue that normal subjects use both action semantics and function from structure inferences simultaneously and interactively to give rise to flexible object-to-goal directed behavior.

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

Background

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

Methodology/Principal Findings

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

Conclusions/Significance

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

Perceptual integration of illusory and imagined kinesthetic images

It is generally agreed that motor imagery involves kinesthetic sensations especially as far as first-person imagery is concerned. It was proposed to determine the extent to which motor imagery and vibration-induced illusory sensations of movement are integrated perceptually. Imagined and illusory hand movements were evoked both separately and in various combinations in 12 volunteers. After each trial, the participants were asked to draw the movement trajectory perceived. In all the subjects, propriomimetic vibration patterns applied to various wrist muscles induced spatially oriented or more complex illusory hand movements such as writing or drawing. Depending on the instructions, the subjects were also able to produce imagined hand movements in various directions and at two different velocities. When straight illusory and imagined movements were evoked simultaneously, all the subjects perceived a single movement trajectory, in which the direction and the velocity of the two ongoing sensations were exactly integrated. This perceptual integration also occurred in the case of more complex movements, such as writing and drawing, giving rise to the perception of original trajectories also combining the features of both motor images. Because these two kinesthetic images, the one intentionally and centrally induced and the other peripherally evoked, activate almost the same neural network including cortical sensory and motor areas, parietal regions, and the cerebellum, these results suggest that common processes may be involved in such a perceptual fusion. The nature of these common processes is discussed, and some fields of research in which these findings could potentially be applied are suggested.

Reading stories activates neural representations of visual and motor experiences

To understand and remember stories, readers integrate their knowledge of the world with information in the text. Here we present functional neuroimaging evidence that neural systems track changes in the situation described by a story. Different brain regions track different aspects of a story, such as a character's physical location or current goals. Some of these regions mirror those involved when people perform, imagine, or observe similar real-world activities. These results support the view that readers understand a story by simulating the events in the story world and updating their simulation when features of that world change.

Reading stories activates neural representations of visual and motor experiences

To understand and remember stories, readers integrate their knowledge of the world with information in the text. Here we present functional neuroimaging evidence that neural systems track changes in the situation described by a story. Different brain regions track different aspects of a story, such as a character's physical location or current goals. Some of these regions mirror those involved when people perform, imagine, or observe similar real-world activities. These results support the view that readers understand a story by simulating the events in the story world and updating their simulation when features of that world change.

Tool use and the distalization of the end-effector

We review recent neurophysiological data from macaques and humans suggesting that the use of tools extends the internal representation of the actor's hand, and relate it to our modeling of the visual control of grasping. We introduce the idea that, in addition to extending the body schema to incorporate the tool, tool use involves distalization of the end-effector from hand to tool. Different tools extend the body schema in different ways, with a displaced visual target and a novel, task-specific processing of haptic feedback to the hand. This distalization is critical in order to exploit the unique functional capacities engendered by complex tools.

Left parietal activation related to planning, executing and suppressing praxis hand movements

OBJECTIVE

We sought to investigate the activity of bilateral parietal and premotor areas during a Go/No Go paradigm involving praxis movements of the dominant hand.

METHODS

A sentence was presented which instructed subjects on what movement to make (S1; for example, "Show me how to use a hammer."). After an 8-s delay, "Go" or "No Go" (S2) was presented. If Go, they were instructed to make the movement described in the S1 instruction sentence as quickly as possible, and continuously until the "Rest" cue was presented 3 s later. If No Go, subjects were to simply relax until the next instruction sentence. Event-related potentials (ERP) and event-related desynchronization (ERD) in the beta band (18-22 Hz) were evaluated for three time bins: after S1, after S2, and from -2.5 to -1.5 s before the S2 period.

RESULTS

Bilateral premotor ERP was greater than bilateral parietal ERP after the S2 Go compared with the No Go. Additionally, left premotor ERP was greater than that from the right premotor area. There was predominant left parietal ERD immediately after S1 for both Go and No Go, which was sustained for the duration of the interval between S1 and S2. For both S2 stimuli, predominant left parietal ERD was again seen when compared to that from the left premotor or right parietal area. However, the left parietal ERD was greater for Go than No Go.

CONCLUSION

The results suggest a dominant role in the left parietal cortex for planning, executing, and suppressing praxis movements. The ERP and ERD show different patterns of activation and may reflect distinct neural movement-related activities.

SIGNIFICANCE

The data can guide further studies to determine the neurophysiological changes occurring in apraxia patients and help explain the unique error profiles seen in patients with left parietal damage.

Hand orientation during reach-to-grasp movements modulates neuronal activity in the medial posterior parietal area V6A

Reach-to-grasp actions involve several components of forelimb movements needed to direct the hand toward the object to be grasped, and to orient and preshape the hand according to the object axis and shape. Area V6A, which represents a node of the dorsomedial frontoparietal circuits, has so far been implicated only in directing the arm toward different spatial locations. The present results confirm this finding and demonstrate, for the first time, that during reach-to-grasp, V6A neurons are also modulated by the orientation of the hand. In the present work the object to be grasped was a handle that could have different orientations. Reach-to-grasp movements were executed in complete darkness while gazing at a small fixation point. The majority of the tested cells (76/142; 54%) turned out to be sensitive to the orientation of the handle. Neurons could be modulated during preparation or execution of reach-to-grasp movements. The most represented cells were those modulated by hand orientation both during preparatory and movement periods. These data show that reaching and grasping are processed by the same population of neurons, providing evidence that the coordination of reaching and grasping takes place much earlier than previously thought, i.e., in the parieto-occipital cortex. The data here reported are in agreement with results of lesions to the medial posterior parietal cortex in both monkeys and humans, and with recent imaging data in humans, all of them indicating a functional coupling in the control of reaching and grasping by the medial parietofrontal circuit.

Effects of TMS on different stages of motor and non-motor verb processing in the primary motor cortex

The embodied cognition hypothesis suggests that motor and premotor areas are automatically and necessarily involved in understanding action language, as word conceptual representations are embodied. This transcranial magnetic stimulation (TMS) study explores the role of the left primary motor cortex in action-verb processing. TMS-induced motor-evoked potentials from right-hand muscles were recorded as a measure of M1 activity, while participants were asked either to judge explicitly whether a verb was action-related (semantic task) or to decide on the number of syllables in a verb (syllabic task). TMS was applied in three different experiments at 170, 350 and 500 ms post-stimulus during both tasks to identify when the enhancement of M1 activity occurred during word processing. The delays between stimulus onset and magnetic stimulation were consistent with electrophysiological studies, suggesting that word recognition can be differentiated into early (within 200 ms) and late (within 400 ms) lexical-semantic stages, and post-conceptual stages. Reaction times and accuracy were recorded to measure the extent to which the participants' linguistic performance was affected by the interference of TMS with M1 activity. No enhancement of M1 activity specific for action verbs was found at 170 and 350 ms post-stimulus, when lexical-semantic processes are presumed to occur (Experiments 1-2). When TMS was applied at 500 ms post-stimulus (Experiment 3), processing action verbs, compared with non-action verbs, increased the M1-activity in the semantic task and decreased it in the syllabic task. This effect was specific for hand-action verbs and was not observed for action-verbs related to other body parts. Neither accuracy nor RTs were affected by TMS. These findings suggest that the lexical-semantic processing of action verbs does not automatically activate the M1. This area seems to be rather involved in post-conceptual processing that follows the retrieval of motor representations, its activity being modulated (facilitated or inhibited), in a top-down manner, by the specific demand of the task.

Motor imagery and its implications for understanding the motor system

In the neurosciences, motor imagery (MIm) has not just been a topic of basic research. It has also attracted attention in applied research as a therapeutic tool. MIm is conceptualized as an internal simulation of motor acts that generates images on the basis of motor representations. Therefore, MIm is associated with neural activation of the cortical and subcortical motor system. The resulting concept of functional equivalence between MIm and execution opens a window to study the organization of motor processes and, more generally, to understand the neural plasticity of the motor system.

Discrete parieto-frontal functional connectivity related to grasping

The human inferior parietal lobule (IPL) is known to have neuronal connections with the frontal lobe, and these connections have been shown to be associated with sensorimotor integration to perform various types of movement such as grasping. The function of these anatomical connections has not been fully investigated. We studied the judgment of graspability of objects in an event-related functional MRI study in healthy subjects, and found activation in two different regions within IPL: one in the left dorsal IPL extending to the intraparietal sulcus and the other in the left ventral IPL. The former region was activated only in the judgment of graspable objects, whereas the latter was activated in the judgment of both graspable and nongraspable objects although the activation was greater for the graspable objects. Psychophysiological interaction analysis showed that these regions had similar but discrete functional connectivity to the lateral and medial frontal cortices. In relation to this particular task, the left dorsal IPL had functional connectivity to the left ventral premotor cortex, supplementary motor area (SMA) and right cerebellar cortex, whereas the left ventral IPL had functional connectivity to the left dorsolateral prefrontal cortex and pre-SMA. These findings suggest that the connection from the left dorsal IPL is associated specifically with automatic flow of information about grasping behavior. By contrast, the connection from the left ventral IPL might be related to motor imagination or enhanced external attention to the presented stimuli.

Action-specific influences on distance perception: a role for motor simulation

Perception is influenced by the perceiver's ability to perform intended actions. For example, when people intend to reach with a tool to targets that are just beyond arm's reach, the targets look closer than when they intend to reach without the tool (J. K. Witt, D. R. Proffitt, & W. Epstein, 2005). This is one of several examples demonstrating that behavioral potential affects perception. However, the action-specific processes that are involved in relating the person's abilities to perception have yet to be explored. Four experiments are presented that implicate motor simulation as a mediator of these effects. When a perceiver intends to perform an action, the perceiver runs a motor simulation of that action. The perceiver's ability to perform the action, as determined by the outcome of the simulation, influences perceived distance.

Interactions between posterior gamma and frontal alpha/beta oscillations during imagined actions

Several studies have revealed that posterior parietal and frontal regions support planning of hand movements but far less is known about how these cortical regions interact during the mental simulation of a movement. Here, we have used magnetoencephalography (MEG) to investigate oscillatory interactions between posterior and frontal areas during the performance of a well-established motor imagery task that evokes motor simulation: mental rotation of hands. Motor imagery induced sustained power suppression in the alpha and beta band over the precentral gyrus and a power increase in the gamma band over bilateral occipito-parietal cortex. During motor imagery of left hand movements, there was stronger alpha and beta band suppression over the right precentral gyrus. The duration of these power changes increased, on a trial-by-trial basis, as a function of the motoric complexity of the imagined actions. Crucially, during a specific period of the movement simulation, the power fluctuations of the frontal beta-band oscillations became coupled with the occipito-parietal gamma-band oscillations. Our results provide novel information about the oscillatory brain activity of posterior and frontal regions. The persistent functional coupling between these regions during task performance emphasizes the importance of sustained interactions between frontal and occipito-parietal areas during mental simulation of action.

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.

Cortical control of gait in healthy humans: an fMRI study

This study examined the cortical control of gait in healthy humans using functional magnetic resonance imaging (fMRI). Two block-designed fMRI sessions were conducted during motor imagery of a locomotor-related task. Subjects watched a video clip that showed an actor standing and walking in an egocentric perspective. In a control session, additional fMRI images were collected when participants observed a video clip of the clutch movement of a right hand. In keeping with previous studies using SPECT and NIRS, we detected activation in many motor-related areas including supplementary motor area, bilateral precentral gyrus, left dorsal premotor cortex, and cingulate motor area. Smaller additional activations were observed in the bilateral precuneus, left thalamus, and part of right putamen. Based on these findings, we propose a novel paradigm to study the cortical control of gait in healthy humans using fMRI. Specifically, the task used in this study--involving both mirror neurons and mental imagery--provides a new feasible model to be used in functional neuroimaging studies in this area of research.

Emulation and Mimicry for Social Interaction: A Theoretical Approach to Imitation in Autism

The “broken-mirror” theory of autism argues that dysfunction of the “mirror neuron system” is a root cause of social disability in autism. The present paper aims to scrutinize this theory and, when it breaks down, to provide an alternative. Current evidence suggests that children with autism are able to understand and emulate goal-directed actions, but may have specific impairments in automatic mimicry of actions without goals. These data are not compatible with the broken-mirror theory, but can be accounted for by a new model called EP-M. The EP-M model segments the mirror neuron system into an indirect, parietal route for goal emulation and planning (EP) and a direct occipital-frontal route for mimicry (M). This fractionation is consistent with neuroimaging and behavioural studies of the mirror neuron system in typical children and adults. I suggest that top-down modulation of the direct M route may be dysfunctional in individuals with autism, leading to abnormal behaviours on mimicry tasks as well as other social disabilities.

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.

Action outcomes are represented in human inferior frontoparietal cortex

The simple action of pressing a switch has many possible interpretations--the actor could be turning on a light, deleting critical files from a computer, or even turning off a life-support system. In each of these cases, the motor parameters of the action are the same but the physical outcome differs. We report evidence of suppressed responses in right inferior parietal and right inferior frontal cortex when participants saw repeated movies showing the same action outcome, but these regions did not distinguish the kinematic parameters by which the action was accomplished. Thus, these brain areas encode the physical outcomes of human actions in the world. These results are compatible with a hierarchical model of human action understanding in which a cascade of specialized processes from occipital to parietal and frontal regions allow humans to understand the physical consequences of actions in the world and the intentions underlying those actions.

Evidence for a distributed hierarchy of action representation in the brain

Complex human behavior is organized around temporally distal outcomes. Behavioral studies based on tasks such as normal prehension, multi-step object use and imitation establish the existence of relative hierarchies of motor control. The retrieval errors in apraxia also support the notion of a hierarchical model for representing action in the brain. In this review, three functional brain imaging studies of action observation using the method of repetition suppression are used to identify a putative neural architecture that supports action understanding at the level of kinematics, object centered goals and ultimately, motor outcomes. These results, based on observation, may match a similar functional-anatomic hierarchy for action planning and execution. If this is true, then the findings support a functional-anatomic model that is distributed across a set of interconnected brain areas that are differentially recruited for different aspects of goal-oriented behavior, rather than a homogeneous mirror neuron system for organizing and understanding all behavior.

The Different Neural Correlates of Action and Functional Knowledge in Semantic Memory: An fMRI Study

Previous reports suggest that the internal organization of semantic memory is in terms of different "types of knowledge," including "sensory" (information about perceptual features), "action" (motor-based knowledge of object utilization), and "functional" (abstract properties, as function and context of use). Consistent with this view, a specific loss of action knowledge, with preserved functional knowledge, has been recently observed in patients with left frontoparietal lesions. The opposite pattern (impaired functional knowledge with preserved action knowledge) was reported in association with anterior inferotemporal lesions. In the present study, the cerebral representation of action and functional knowledge was investigated using event-related analysis of functional magnetic resonance imaging data. Fifteen subjects were presented with pictures showing pairs of manipulable objects and asked whether the objects within each pair were used with the same manipulation pattern ("action knowledge" condition) or in the same context ("functional knowledge" condition). Direct comparisons showed action knowledge, relative to functional knowledge, to activate a left frontoparietal network, comprising the intraparietal sulcus, the inferior parietal lobule, and the dorsal premotor cortex. The reverse comparison yielded activations in the retrosplenial and the lateral anterior inferotemporal cortex. These results confirm and extend previous neuropsychological data and support the hypothesis of the existence of different types of information processing in the internal organization of semantic memory.

Neural correlates of state estimation in visually guided movements: an event-related fMRI study

State estimation of self-movement, based on both motor commands and sensory feedback, has been suggested as essential to human movement control to compensate for inherent feedback delays in sensorimotor loops. The present study investigated the neural basis for state estimation of human movement using event-related functional magnetic resonance imaging (fMRI). Participants traced visually presented curves with a computer mouse, and an artificial delay was introduced to visual feedback. Motor performance and brain activities during movements were measured. Experiment 1 investigated brain activations that were significantly correlated with visual feedback delay and motor error by parametrically manipulating visual feedback delay. Activation of the right posterior parietal cortex (PPC) was positively correlated with motor error, whereas activation of the right temporo-parietal junction (TPJ) was observed only in the group with a smaller increase in motor error with increased visual feedback delay. Experiment 2 involved parametric analysis of motor performance while controlling mouse movement speed during the task. Activity in the right TPJ showed a significant positive correlation with motor performance under the delayed visual feedback condition. In addition, activity of the PPC was greater when motor error was presented visually. These results suggest that the PPC plays a significant role in evaluating visuomotor prediction error, while the TPJ is involved in state estimation of self-movement during visually guided movements.

Influence of body segment position during in-phase and antiphase hand and foot movements: a kinematic and functional MRI study

Behavioral studies have provided important insights into the mechanisms governing interlimb coordination. In this study, we combined kinematic and functional magnetic resonance imaging (fMRI) analysis to investigate the brain cortical and subcortical areas involved in interlimb coordination and the influence of direction of movement and of body segment position on the activity of those areas. Fifteen right-handed healthy subjects were studied while performing cyclic in-phase and antiphase hand and foot movements with the dominant, right limbs, with the upper limb positioned either prone or supine, and in front or behind with respect to the trunk. When contrasting antiphase to in-phase movements, fMRI analysis demonstrated an increased recruitment of a widespread sensorimotor network (including regions in the frontal and parietal lobes, bilaterally, the cingulated motor area, the thalami, the visual cortex, and the cerebellum) considered to function in motor, sensory, and multimodal integration processing. When contrasting the anterior to the posterior position of the upper limb with respect to the trunk, we found different recruitment patterns in the frontal and parietal regions as well as the preferential recruitment of the basal ganglia, the insula, and the cerebellum during the first condition and of regions located in the temporal lobes during the second one. Different brain areas are engaged at a different extent during interlimb coordination. In addition to the relative difficulty of the movement, the different cognitive and sensorial loads needed to control and perform the motor act might be responsible for these findings.

Mental practice with motor imagery: evidence for motor recovery and cortical reorganization after stroke

OBJECTIVES

To measure the efficacy of a program combining mental and physical practice with the efficacy of a program composed of only constraint-induced movement therapy (CIMT) or only mental practice on stroke patients' levels of upper-extremity impairment and upper-extremity functional outcomes and to establish the relationship between changes in blood-oxygen-level dependent (BOLD) functional magnetic resonance imaging response during a specific motor or imagery task and improvement in motor function between intervention groups.

DESIGN

Case series.

SETTING

Licensed, 56-bed, freestanding, university-affiliated rehabilitation hospital.

PARTICIPANTS

Three men and 1 woman with moderate upper-limb hemiparesis after stroke were randomized.

INTERVENTIONS

Two patients received mental practice and CIMT, 1 patient received only mental practice, and 1 received only CIMT.

MAIN OUTCOME MEASURES

Wolf Motor Function Test (WMFT), Motor Activity Log (MAL), Sirigu break test, Movement Imagery Questionnaire-Revised, and Vividness of Movement Imagery Questionnaire.

RESULTS

The mental practice intervention alone led to slight improvement in certain functional and mental imagery measures (Sirigu, MAL, WMFT) but did not result in a clinically meaningful improvement with notable right cerebellar hemisphere activation that was not present before intervention. After CIMT, only the single patient showed clinically meaningful improvement of his affected hand as exhibited by decreased times on the MAL and WMFT. The patient showed increased bilateral cortical activation in both the motor and premotor areas during execution of a finger flexion and extension task. In contrast, during a second task, which was an imagined flexion and extension task, motor, occipital, and inferior parietal activation mainly in the contralateral hemisphere were observed. After 2 weeks of CIMT plus mental practice a patient with a lesion restricted to the parietal cortex showed little improvement in upper-extremity function and mental imagery in comparison with the patient with damage to nonparietal areas, who showed clinically meaningful improvement. The pattern of activation after 2 weeks of CIMT plus mental practice in the patient with nonparietal damage led to more focal contralateral activation in primary motor cortex when executing a voluntary flexion and extension task.

CONCLUSIONS

The case series indicates that for these patients with chronic, moderate upper-extremity impairment after stroke, a 2-week regimen of CIMT or CIMT plus mental practice only (in 1 case) resulted in modest changes occurring as a decrease in impairment, with functional improvement. Mental practice alone did not result in a clinically meaningful improvement in upper-limb impairment. We describe how these interventions may elicit "plastic" changes in the brain. Further investigations to determine the appropriate delivery and dosing of both physical and mental practice, as well as to determine whether mental practice-induced changes positively correlate with distinct patterns of cortical activation, should be undertaken before the efficacy of their use can be ascertained among patients with limitations comparable with these participants.

Stimulus properties matter more than perspective: an fMRI study of mental imagery and silent reading of action phrases

The role of the primary motor cortex (M1) in tasks involving action words remains controversial. Therefore, we investigated whether the previously reported involvement of M1 in processing of action words results from the semantic representation of action words per se, or if M1 activation may actually depend on whether or not subjects (explicitly or automatically) adopt a strategy of simulating the movements. Subjects silently read short phrases describing a situation which either involved a motor scene or not (STIMULUS: motor, non-motor phrases) and performed a secondary task: either they were explicitly asked to imagine the situation or they performed letter detection preventing them from using a simulation strategy (TASK: imagery vs. letter detection). In addition, phrases were presented both in 1st and 3rd person singular (

PERSPECTIVE

1st vs. 3rd person). This allowed us to investigate the influence of the secondary tasks (letter detection versus explicit motor imagery) on the neural activity in M1 during the processing of motor and non-motor phrases. We found differential left M1 activity in the task by stimulus interaction with enhanced M1 activation for imagery in the presence of motor phrases (vs. non-motor phrases) compared to letter detection of motor vs. non-motor phrases. This M1-activity was not differentially modulated by perspective. Therefore, M1 activation previously found in experiments of silent reading of action words may have resulted from the subjects' strategy to mentally simulate the movements during the processing of action words.

Cerebral compensation during motor imagery in Parkinson's disease

In neurodegenerative disorders, neural damage can trigger compensatory mechanisms that minimize behavioural impairments. Here, we aimed at characterizing cerebral compensation during motor imagery in Parkinson's disease (PD), while controlling for altered motor execution and sensory feedback. We used a within-patient design to compare the most and least affected hand in 19 right-handed PD patients with markedly right-lateralized symptoms. We used a motor imagery (MI) task in which the patients were required to judge the laterality of hand images, rotated either in a lateral or in a medial orientation with respect to the body sagittal plane. This design allowed us to compare cerebral activity (using fMRI) evoked by MI of each hand separately, while objectively monitoring task performance. Reaction times and parieto-premotor activity increased in a similar manner as a function of stimulus rotation during motor imagery of left and right hands. However, patients were markedly slower when judging images of the affected hand in lateral orientations, and there was a corresponding increase in activity in the right extrastriate body area (EBA) and occipito-parietal cortex during mental rotation of the affected hand. Furthermore, these regions increased their connectivity towards the left PMd for right (affected) hands in a lateral orientation. We infer that, in strongly lateralized PD patients, motor imagery of the most-affected hand exploits additional resources in extrastriate visual areas. These findings characterize the cerebral bases of the increased dependence on visual information processing during the generation of motor plans in PD, pointing to its compensatory role.

Human Neural Systems for Conceptual Knowledge of Proper Object Use: A Functional Magnetic Resonance Imaging Study

Ideational apraxia is characterized by impaired knowledge of action concepts and proper object usage. The present functional magnetic resonance imaging study aimed at investigating the neural system underlying conceptual knowledge for proper object use in healthy subjects, when the effects of visuospatial properties and perceptual modality were taken into account. Subjects performed semantic decision tasks requiring retrieval of knowledge about either object functional purposes (functional task) or visuospatial object properties (visuospatial task) and perceptual control tasks. The semantic tasks were performed with pairs of either written object names or object drawings. Activation for the functional task in common for words and pictures, compared with the visuospatial and control tasks, was found in left parietal-temporal-occipital (PTO) junction, inferior frontal, anterior dorsal premotor, and presupplementary motor areas. Ventral inferior frontal cortex activation correlated negatively with reaction time in the functional condition. No specific activation characterized the visuospatial task compared with the functional task. The conceptual tasks, compared with the control tasks, demonstrated overlapping activation in left PTO junction, prefrontal, dorsal premotor, cuneus, and inferior temporal areas. These results outline the neural processes underlying conceptual knowledge for proper object use. The left ventral inferior frontal gyrus might facilitate behavioral decisions regarding functional/pragmatical object properties.

Modulation of neural activity during observational learning of actions and their sequential orders

How does the brain transform perceptual representations of others' actions into motor representations that can be used to guide behavior? Here we used functional magnetic resonance imaging to record human brain activity while subjects watched others construct multipart objects under varied task demands. We find that relative to resting baseline, passive action observation increases activity within inferior frontal and parietal cortices implicated in action encoding (mirror system) and throughout a distributed network of areas involved in motor representation, including dorsal premotor cortex, pre-supplementary motor area, cerebellum, and basal ganglia (experiments 1 and 2). Relative to passive observation, these same areas show increased activity when subjects observe with the intention to subsequently reproduce component actions using the demonstrated sequential procedures (experiment 1). Observing the same actions with the intention of reproducing component actions, but without the requirement to use the demonstrated sequential procedure, increases activity in the same regions, although to a lesser degree (experiment 2). These findings demonstrate that when attempting to learn behaviors through observation, the observers' intentions modulate responses in a widely distributed network of cortical and subcortical regions implicated previously in action encoding and/or motor representation. Among these regions, only activity within the right intraparietal sulcus predicts the accuracy with which observed procedures are subsequently performed. Successful formation of motor representations of sequential procedures through observational learning is dependent on computations implemented within this parietal region.

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.

Posture influences motor imagery: An fMRI study

Motor imagery is widely used to study cognitive aspects of the neural control of action. However, what is exactly simulated during motor imagery is still a matter of debate. On the one hand, it is conceivable that motor imagery is an embodied cognitive process, involving a simulation of movements of one's own body. The alternative possibility is that, although motor imagery relies on knowledge of the motor processes, it does not entail an actual motor simulation that is influenced by the physical configuration of one's own body. Here we discriminate between these two hypotheses, in the context of an established motor imagery task: laterality judgments of rotated hand drawings. We found that reaction times of hand laterality judgments followed the biomechanical constraints of left or right hand movements. Crucially, the position of subjects' own left and right arm influenced laterality judgments of left and right hands. In neural terms, hand laterality judgments activated a parieto-frontal network. The activity within this network increased with increasing biomechanical complexity of the imagined hand movements, even when the amount of stimulus rotation was identical. Moreover, activity in the intraparietal sulcus was modulated by subjects' own hand position: a larger incongruence in orientation between the subjects' hand and the stimulus hand led to a selective increase in intraparietal activity. Our results indicate that motor imagery generates motor plans that depend on the current configuration of the limbs. This motor plan is calculated by a parieto-frontal network. Within this network, the posterior parietal cortex appears to incorporate proprioceptive information related to the current position of the body into the motor plan.