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

Abstract

Explicit motor imagery Conversion paralysis fMRI Mental rotation a b s t r a c tMotor 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 IntroductionMotor imagery is a familiar aspect of most people's everyday experience. It is important for learning complex motor skills like sports (Murphy, 1994), as well as re-learning motor skills in neurological populations (Dijkerman et al., 2004;. The potential of motor imagery in clinical applications is broad, ranging from Brain-Computer interfacing (Pfurtscheller and Neuper, 2006)

Brain circuits implicated in psychogenic paralysis in conversion disorders and hypnosis

“…3C), unlike healthy participants. Altogether, even though the existing results are still scarce and partly inconsistent across studies and conversion domains, recent neuroimaging data for non-motor deficits show some convergence with those obtained in patients with motor conversion paralysis in several studies [18,24,25,56,106]. Thus, an emerging pattern of findings across domains points to not only abnormal recruitment of brain areas involved in conscious control of movement or conscious sensory perception, but also heightened activation of both cortical (VMPFC, precuneus) and subcortical (amygdala, thalamus, striatum) areas thought to be normally involved in emotional regulation of behavior and memory.…”

“…In patients with motor loss (n = 7), primary motor cortex activated normally during mental imagery of hand rotation for both the intact and impaired side but was accompanied by increased activity in ventromedial prefrontal cortex (VMPFC) during implicit imagery for the left hand only. From de Lange et al, [25]. B.…”

“…de Lange et al [24,25] examined a group of 7 patients during an explicit motor imagery task, where they were asked to imagine actions with their right or left hand, as well as during an implicit motor task, where they were asked to make rotation judgments for right or left hand pictures. Both tasks are known to induce covert mental simulation of hand movements and activate primary motor cortical areas in healthy people [66].…”

“…Both tasks are known to induce covert mental simulation of hand movements and activate primary motor cortical areas in healthy people [66]. In these studies, motor conversion patients showed a normal behavioral pattern in response times and normal activation in motor cortices regardless of hand side [24,25], reminiscent of normal activation during motor preparation in our Go/NoGo task [18,49]. In addition, de Lange et al [24,25] also found a distinctive activation in VMPFC in conversion patients during imagery conditions involving the affected hand side, although this was observed only in the implicit task (Fig.…”

Motor Imagery of the Unaffected Hand in Children With Spastic Hemiplegia

“…Motor imagery refers to the imagination of a movement, without any overt movement execution (de Lange, Roelofs, & Toni, 2008) and is essentially an internal representation of a movement. According to Johnson's imagery as planning theory (Johnson, 2000), movement planning involves a subconscious unfolding of these representations, which allow the most appropriate motor plan to be selected and implemented.…”