Motor imagery: A window into the mechanisms and alterations of the motor system (original) (raw)
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Increased self-monitoring during imagined movements in conversion paralysis
Neuropsychologia, 2007
Conversion paralysis is characterized by a loss of voluntary motor functioning without an organic cause. Despite its prevalence among neurological outpatients, little is known about the neurobiological basis of this motor dysfunction. We have examined whether the motor dysfunction in conversion paralysis can be linked to inhibition of the motor system, or rather to enhanced self-monitoring during motor behavior.
Altered connectivity between prefrontal and sensorimotor cortex in conversion paralysis
Neuropsychologia, 2010
Conversion paralysis (CP) is a frequent and impairing psychiatric disorder, affecting voluntary motor function. Yet, we have previously shown that the motor system of CP patients with a unilateral conversion paresis is recruited to a similar degree during imagined movements of the affected and unaffected limb. In contrast, imagery of movements with the affected limb results in larger prefrontal activation. It remains unclear how this hand-specific increased prefrontal activity relates to the reduced responsiveness of motor and somatosensory areas, a consistent and important feature of CP patients.
Imagined paralysis reduces motor cortex excitability
Psychophysiology, 2022
Neuroimaging research on mental imagery has shown that visual and motor mental imagery systematically activate sensory and motor brain areas, respectively (e.g., Decety, 1996; Jeannerod, 1995; Kosslyn et al., 1993), suggesting that mental imagery can have neurophysiological consequence similar to those during real sensory and motor experiences. While the exact mechanisms underlying mental imagery are still open to debate (Foglia & O'Regan, 2016; Pearson & Kosslyn, 2015), mental imagery has widely been used as a tool to improve cognitive and motor skills in various disciplines (e.g., Schuster et al., 2011). For example, motor imagery is used to improve athletes' performances (e.g., Guillot et al., 2012; Hall et al., 1990), and also to support rehabilitation in patients suffering from motor deficits (e.g.,
2012
There is now compelling evidence that motor imagery (MI) and actual movement share common neural substrate. However, the question of how MI inhibits the transmission of motor commands into the efferent pathways in order to prevent any movement is largely unresolved. Similarly, little is known about the nature of the electromyographic activity that is apparent during MI. In addressing these gaps in the literature, the present paper argues that MI includes motor execution commands for muscle contractions which are blocked at some level of the motor system by inhibitory mechanisms. We first assemble data from neuroimaging studies that demonstrate that the neural networks mediating MI and motor performance are not totally overlapping, thereby highlighting potential differences between MI and actual motor execution. We then review MI data indicating the presence of subliminal muscular activity reflecting the intrinsic characteristics of the motor command as well as increased corticomotor excitability. The third section not only considers the inhibitory mechanisms involved during MI but also examines how the brain resolves the problem of issuing the motor command for action while supervising motor inhibition when people engage in voluntary movement during MI.The last part of the paper draws on imagery research in clinical contexts to suggest that some patients move while imagining an action, although they are not aware of such movements. In particular, experimental data from amputees as well as from patients with Parkinson's disease are discussed. We also review recent studies based on comparing brain activity in tetraplegic patients with that from healthy matched controls that provide insights into inhibitory processes during MI. We conclude by arguing that based on available evidence, a multifactorial explanation of motor inhibition during MI is warranted.
Motor Imagery in Mental Rotation: An fMRI Study
NeuroImage, 2002
Twelve right-handed men performed two mental rotation tasks and two control tasks while whole-head functional magnetic resonance imaging was applied. Mental rotation tasks implied the comparison of different sorts of stimulus pairs, viz. pictures of hands and pictures of tools, which were either identical or mirror images and which were rotated in the plane of the picture. Control tasks were equal except that stimuli pairs were not rotated. Reaction time profiles were consistent with those found in previous research. Imaging data replicate classic areas of activation in mental rotation for hands and tools (bilateral superior parietal lobule and visual extrastriate cortex) but show an important difference in premotor area activation: pairs of hands engender bilateral premotor activation while pairs of tools elicit only left premotor brain activation. The results suggest that participants imagined moving both their hands in the hand condition, while imagining manipulating objects with their hand of preference (right hand) in the tool condition. The covert actions of motor imagery appear to mimic the "natural way" in which a person would manipulate the object in reality, and the activation of cortical regions during mental rotation seems at least in part determined by an intrinsic process that depends on the afforded actions elicited by the kind of stimuli presented. © 2002 Elsevier Science (USA)
fMRI in Patients With Motor Conversion Symptoms and Controls With Simulated Weakness
Psychosomatic Medicine, 2007
Background: Conversion disorder (motor type) describes weakness that is not due to recognized disease or conscious simulation but instead is thought to be a "psychogenic" phenomenon. It is a common clinical problem in neurology but its neural correlates remain poorly understood. Objective: To compare the neural correlates of unilateral functional weakness in conversion disorder with those in healthy controls asked to simulate unilateral weakness. Methods: Functional magnetic resonance imaging (fMRI) was used to examine whole brain activations during ankle plantarflexion in four patients with unilateral ankle weakness due to conversion disorder and four healthy controls simulating unilateral weakness. Group data were analyzed separately for patients and controls. Results: Both patients and controls activated the motor cortex (paracentral lobule) contralateral to the "weak" limb less strongly and more diffusely than the motor cortex contralateral to the normally moving leg. Patients with conversion disorder activated a network of areas including the putamen and lingual gyri bilaterally, left inferior frontal gyrus, left insula, and deactivated right middle frontal and orbitofrontal cortices. Controls simulating weakness, but not cases, activated the contralateral supplementary motor area. Conclusions: Unilateral weakness in established conversion disorder is associated with a distinctive pattern of activation, which overlaps with but is different from the activation pattern associated with simulated weakness. The overall pattern suggests more complex mental activity in patients with conversion disorder than in controls.
Electrophysiological correlates of motor conversion disorder
Movement Disorders, 2008
In patients with a functional (psychogenic) paresis, motor conduction tests are, by definition, normal. We investigated whether these patients exhibit an abnormal motor excitability. Four female patients with a functional paresis of the left upper extremity were studied using transcranial magnetic stimulation (TMS). We investigated motor thresholds, intracortical inhibition and intracortical facilitation at rest. Corticospinal excitability was evaluated by single pulse TMS during rest and during imagination of tonic index finger adductions. Data obtained from the affected first dorsal interosseous muscle were compared with the unaffected hand and with a healthy age-matched control group. Three patients demonstrated a flaccid paresis, one patient had a psychogenic dystonia. Motor thresholds, short interval intracortical inhibi-tion and intracortical facilitation recorded from the affected side were normal. In healthy subjects, movement imagination produced an increase of corticospinal excitability. In the patients, motor imagery with the affected index finger resulted in a decrease of corticospinal excitability compared to rest, being significantly different from the unaffected side and from the control group. We suggest that suppression of corticospinal excitability during movement imagination is an electrophysiological correlate of the patients' inability to move voluntarily and provides some insight into the pathophysiology of this disorder.
Motor imagery beyond the joint limits: A transcranial magnetic stimulation study
The processes and neural bases used for motor imagery are also used for the actual execution of correspondent movements. Humans, however, can imagine movements they cannot perform. Here we explored whether plausibility of movements is mapped on the corticospinal motor system and whether the process is influenced by visuomotor vs. kinesthetic-motor first person imagery strategy. Healthy subjects imagined performing possible or biomechanically impossible right index finger movements during single pulse TMS of the left motor cortex. We found an increase of corticospinal excitability during motor imagery which was higher for impossible than possible movements and specific for the muscle involved in the actual execution of the imagined movement. We expand our previous action observation studies, suggesting that the plausibility of a movement is computed in regions upstream the primary motor cortex, and that motor imagery is a higher-order process not fully constrained by the rules that govern motor execution.