Slowing of Motor Imagery after a Right Hemispheric Stroke

Hindawi Publishing Corporation Stroke Research and Treatment Volume 2012, Article ID 297217, 10 pages doi:10.1155/2012/297217 Clinical Study Slowing of Motor Imagery after a Right Hemispheric Stroke Francine Malouin,1 Carol L. Richards,1 and Anne Durand2 1 Department of Rehabilitation, Laval University and Center for Interdisciplinary Research in Rehabilitation and Social Integration (CIRRIS), IRDPQ 525 Boulevard Hamel East, Quebec City, QC, Canada G1M 2S8 2 Institut de Réadaptation en Déficience Physique de Québec, 525 Boulevard Hamel East, Quebec City, QC, Canada G1M 2S8 Correspondence should be addressed to Francine Malouin, Received 13 October 2011; Revised 11 January 2012; Accepted 7 February 2012 Academic Editor: Keh-chung Lin Copyright © 2012 Francine Malouin et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The temporal congruence between real and imagined movements is not always preserved after stroke. We investigated the dependence of temporal incongruence on the side of the hemispheric lesion and its link with working memory deficits. Thirtyseven persons with a chronic stroke after a right or left hemispheric lesion (RHL : n = 19; LHL : n = 18) and 32 age-matched healthy persons (CTL) were administered a motor imagery questionnaire, mental chronometry and working memory tests. In contrast to persons in the CTL group and LHL subgroup, persons with a RHL had longer movement times during the imagination than the physical execution of stepping movements on both sides, indicating a reduced ability to predict movement duration (temporal incongruence). While motor imagery vividness was good in both subgroups, the RHL group had greater visuospatial working memory deficits. The bilateral slowing of stepping movements in the RHL group indicates that temporal congruence during motor imagery is impaired after a right hemispheric stroke and is also associated with greater visuospatial working memory deficits. Findings emphasize the need to use mental chronometry to control for movement representation during motor imagery training and may indicate that mental practice through motor imagery will have limitations in patients with a right hemispheric stroke. 1. Introduction Motor imagery, which is the imagining of actions without their execution, can be defined as an active process during which the representation of a specific action is internally reproduced within working memory without any overt output [1]. The rationale for using motor imagery in the rehabilitation of motor impairments likely arises from the functional correlates that motor imagery shares with the execution of physical movement. For instance, the duration of imagined movements correlates with the duration of real movements [2, 3], simulation of movements evokes similar autonomic responses [4, 5], and, more importantly, the imagination of an action engages largely similar neural networks as its physical execution, notably motor and premotor areas and parietal cortices [6–8]. These observations suggest that real and covert movements during motor imagery obey similar principles and share similar mechanisms. Temporal characteristics of motor imagery have been extensively studied with mental chronometry in healthy individuals [9]. Studies that examined the temporal relationship between the physical execution of a motor task (i.e., writing, walking, pointing, stepping) and the imagination of the same task (mental chronometry) have found that the imagination and execution times are generally similar (temporal congruence or functional equivalence). In addition, it has been shown that Fitt’s law, which states that more difficult movements take more time to produce physically than easier ones, applies also to imagined movements [3] indicating that the timing of movements, either performed physically or imagined, is subject to common laws and principles [10]. For this reason, mental chronometry has been used by many to examine the effects of brain lesions on the temporal organization of motor imagery [11–16], to assess MI ability [9, 17, 18] and to control whether patients are engaged in mental rehearsal during mental practice [19]. 2 While some studies have shown that, following a unilateral lesion of the motor cortex, movements are slower on the affected limbs during both the physical execution and mental simulation of the same movement confirming temporal congruence [11, 12], others have reported that patients with lesions restricted to the superior regions of the parietal cortex could not predict through mental imagery the time necessary to perform various finger movements and visually guided pointing gestures, suggesting that the parietal cortex is important for the ability to generate mental movement representations [13]. More recently, temporal incongruence has been described following stroke during motor imagery of upper limb [14–16] and lower limb [14] movements. In these studies, in contrast to control subjects, patients showed simulation times that were longer than real movement times (overestimation of movement duration) indicative of a slowing of the motor imagery process, especially in persons with right hemispheric (RH) strokes [15, 16]. In the six patients with RH stroke showing a slowing of motor imagery, the corticomotor excitability, as measured with transcranial magnetic stimulation, was not increased during imagery conditions [16] suggesting that facilitation of motor cortex excitability during motor imagery depends on input from regions of the right hemisphere which can be disrupted by right hemispheric stroke. Because in prior studies limb dominance of the patients was not controlled [14–16] and the number of patients with a right and a left hemispheric lesion was small [15, 16] or uneven [14], no definite conclusion can be drawn as to the impact of the lesion side on temporal incongruence between real and imagined movements. The present study sought to extend these prior findings in a larger sample of patients with right and left hemispheric stroke having similar limb dominance. In addition, since motor imagery is an active process during which the representation of a specific action is internally reproduced within working memory [1] and given the role of the right cerebral hemisphere in image generation [20] and visuospatial working memory [21, 22], we also examined whether lesion side had an impact on visuospatial working memory performance. It was hypothesized that right hemispheric lesions (RHLs) would be associated with both a slowing of motor imagery and greater visuospatial working memory deficits. The aims of this study were to determine whether the slowing of motor imagery after stroke is linked to the side of the cerebral lesion and, further, if it is associated with an impairment of visuospatial short-term (...truncated)