中风后运动想象能力的恢复

Hindawi Publishing Corporation Rehabilitation Research and Practice Volume 2011, Article ID 283840, 9 pages doi:10.1155/2011/283840 Research Article Recovery of Motor Imagery Ability in Stroke Patients Sjoerd de Vries,1 Marga Tepper,2 Bert Otten,1 and Theo Mulder1, 3 1Centre for Human Movement Sciences, University Medical Centre Groningen, University of Groningen, P.O. Box 196, 9700 AD Groningen, The Netherlands 2Centre for Rehabilitation, University Medical Centre Groningen, 9700 RD Groningen, The Netherlands 3Royal Netherlands Academy of Arts and Sciences, 1011 JV Amsterdam, The Netherlands Correspondence should be addressed to Sjoerd de Vries, devriessj@gmail.com Received 27 September 2010; Revised 26 January 2011; Accepted 8 February 2011 Academic Editor: Nicola Smania Copyright © 2011 Sjoerd de Vries et al. This is an open access article distributed under the Creative CommonsAttribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Objective. To investigate whether motor imagery ability recovers in stroke patients and to see what the relationship is between different types of imagery andmotor functioning after stroke.Methods. 12 unilateral stroke patients were measured at 3 and 6weeks poststroke on 3 mental imagery tasks. Arm-hand function was evaluated using the Utrecht Arm-Hand task and the Brunnstro¨m Fugl-Meyer Scale. Age-matched healthy individuals (N = 10) were included as controls. Results. Implicit motor imagery ability and visual motor imagery ability improved significantly at 6 weeks compared to 3 weeks poststroke. Conclusion. Our study shows that motor imagery can recover in the first weeks after stroke. This indicates that a group of patients who might not be initially selected for mental practice can, still later in the rehabilitation process, participate in mental practice programs. Moreover, our study shows that mental imagery modalities can be differently affected in individual patients and over time. 1. Introduction Recently, several researchers have proposed the use of mental practice to facilitate motor recovery in stroke patients and other patients with motor disorders [1, 2]. Mental practice is a training method where imagination of movements, without actually moving, is used with the intention of improving motor performance. In other words, mental practice is the imagined rehearsal of a movement with the specific intent of improving that movement [3]. Several lines of research have shown that mental practice improves motor performance in healthy participants [4, 5] as well as in stroke patients [6–9]. Mental practice is suggested to work because the motor control structures in the brain are activated in more or less the same way as during the actual performance of movements [10, 11]. Indeed, studies with healthy individuals have shown that motor imagery and actual action share some striking similarities. When someone is asked to perform amovement, for example, “walk along this line”, and to imagine the same movement, the time to complete the actual walking movement is similar to the time needed for completing the imagined walking movement [12]. Moreover, neuroimaging studies have shown that during motor imagery the same brain areas are active as during actual movement [13– 17]. Hence, also in stroke patients there should be a relation between motor function and motor imagery ability. However, the reported results thus far are not consistent [18]. One factor that might explain these ambiguous results, as suggested by Daprati et al. [18], is the heterogeneous manner in which motor imagery ability is assessed. The researchers that have used motor imagery assessments have used differ- ent types of motor imagery tasks. Motor imagery ability is a complex cognitive capacity which is, until now, not fully understood and has an intricate relationship with other types of imagery. First, motor imagery can be divided into two different types. We can explicitly imagine movements of a limb. Here imagery is conscious and involves, for example, the voluntary active imagination of “reaching for a cup on the table with your right arm”. This type of imagery is known as explicit motor imagery and there exist a number of studies with stroke patients that used imagery tasks that depended on explicit motor imagery [19–25]. On the other hand, we can be tricked into motor imagery implicitly by, for example, answering a question about the handedness (left-right) of 2 Rehabilitation Research and Practice a picture of a hand, or by answering with which kind of grip we would prefer to grasp a cup of coffee or a dowel in a particular orientation. This type of imagery is known as implicit motor imagery and is also used in a number of studies with stroke patients [26–29]. Secondly, motor imagery is also related to other cognitive processes such as reflected in tasks that rely on the mental rotation of pictures, so called visual imagery tasks. A well- known example of visual imagery is the Shepard Meltzer task where two three-dimensional figures are pictured side to side in different orientations, and the respondent has to answer the question whether these figures are similar or not [30]. Recent neuroimaging data have shown that, although these different types of imagery, implicit, explicit and visual imagery, share similar neural processes, at the same time they also differ in the underlying mechanisms [31–34] suggesting that these types of imagery can be affected differently after hemiparetic stroke. A second factor that could explain why the relationship between motor function and motor imagery is less clear after stroke, is related to the poststroke moment when motor imagery ability is assessed. The differences in the time since stroke when motor imagery was assessed varies largely between studies, ranging from weeks [28] to years [29] poststroke. Stroke has, indeed, more cognitive effects early after stroke than later after stroke [35] therefore, performance on motor imagery ability assessment could well be influenced by the moment of assessment. In other words, the moment of assessment could differently affect the imagery modalities that are used in the experiments of individual stroke patients. Until now, no study has followed the recovery process of motor imagery and motor functioning, in parallel during the rehabilitation period. Because of the multifaceted nature of motor imagery and its relation to visual imagery the present study was designed to assess the relation of different imagery types and motor function to see to what extend they relate and if they recover in parallel after 3 weeks. The purposes of the research was (1) to measure imagery ability of hemiparetic stroke patients 3 weeks poststroke and 6 weeks poststroke (2) to find out whether motor imagery ability improved in parallel to arm-hand functioning and (3) to see what relationship exists between different types of imagery and motor functioning after hemiparetic stroke. 2. Methods 2.1. Subjects. Twelve hemiparetic stroke patients (4 female, mean age = 59.75 years, SD= 11.98 years, 1 left handed) who suffered a first unilateral stroke 3 weeks earlier (M = 22.8 days; SD= 3.5 days) participated in this study. The patients were recruited from the stroke unit of a rehabilitation centre. Six patients were classified as left hemiparetic and 6 patients were classified as right hemiparetic. All subjects gave informed, written consent. The experiment was conducted in accordance with the Declaration of Helsinki and approved by the local ethics committee of the medical centre of the University of Groningen. The inclusion criteria were patients with a hemiparetic arm/hand secondary to a stroke, with no explicit age limit. Exclusion criteria were multiple strokes, comorbidity which interfered with the objectives of the study, severe perceptual problems and severe cognitive impairments, severe aphasia, and other neurologic conditions that interfered with the goal of the study. During the study, the rehabilitation program remained unaltered for all participating patients. Age-matched healthy individuals (N = 10, 5 female, mean age 55, SD= 10.22 years, 2 left handed) were included as a control group. 2.2. Instruments 2.2.1. Implicit Motor Imagery Ability. Motor imagery ability was measured by means of a mental rotation task, namely, a hand laterality judgement task, known for its clinical value in measuring motor imagery ability [36–38]. Subjects had to decide as fast as possible whether a rotated picture of a hand on a computer screen was a left or a right hand by pushing 1 of 2 buttons (L/R) with their nonimpaired limb. 2.2.2. Visual Imagery. A mental rotation task known to depend on a visual imagery strategy was used to measure visual imagery [34]. In the visual imagery task, subjects were asked to determine as fast as possible whether a rotated picture was a normal canonical letter or its mirror image by pushing 1 of 2 buttons with their nonimpaired hand. The order of the implicit motor imagery task and the visual imagery task was counterbalanced between subjects. The implicit motor imagery and visual imagery tasks were both divided in 4 blocks. Each block contained 72 stimuli, yielding a total of 288 stimuli per task. Prior to each task, a practice block was presented, containing 48 stimuli. All stimuli were presented randomly at the centre of the computer screen with a random delay between 2 and 3 s. The stimuli were rotated, presented in 60◦ increments from the upright position between 0◦ and 300◦. Zero degrees for hand stimuli was a hand pictured in an upright position with fingers pointing upwards. Zero degrees for letter stimuli was a picture of the letter F or R in an upright position. Stimuli remained on the screen until the participant responded, or when 10 s had expired. After each block, there was a short rest period. For each task the mean accuracy scores (ACC) for each subject were calculated as the proportion of correct responses, yielding a minimum score of 0% (all wrong) and a maximum score of 100% (all correct). For each task the mean reaction times (RT) for each subject were calculated on RTs between 350ms and 10,000ms (excluding anticipated responses). In both mental imagery tasks, responses were given by pushing 1 of 2 buttons with the nonparetic hand. This hand could be either the dominant or the nondominant hand. To control for confounding dominant nondominant hand effects, the control group executed the mental imagery task with both the dominant and nondominant hand in a counterbalanced order. For the rest of the experiment, all conditions for patients and controls were equal. Rehabilitation Research and Practice 3 (a) (b) (c) (d) Figure 1: Example of a 4-choice solution of the arm end position after the instructions in the explicit motor imagery task. 2.2.3. Explicit Motor Imagery Ability. The hand laterality task measured motor imagery implicitly. However, since implicit and explicit motor imagery measure different components of motor imagery, we also used a motor imagery task that measured the explicit motor imagery ability of the patients. During explicit imagery tasks, subjects were asked to imagine moving their limbs in a particular way (e.g., “imagine flexing your underarm 90 degrees”). We asked subjects to close their eyes and to imagine as vividly as possible a movement with their hand, without actual movement, in a series of steps. For example, stepwise instruction for one item of the explicit motor imagery task were “Step 1: Place both hands, palm facing down on the marks on the table in front of you. Step 2: Turn your wrist 90 degrees until your palm is facing inwards. Step 3: Flex your underarm 90 degrees until it your hand is touching your chest. Step 4: Flex your arm upwards 90 degrees until your hand is pointing to the ceiling. Step 5: Extend your arm 90 degrees until it reaches the tabletop”. After the instructions, the subjects had to indicate what the position of his or her imagined hand was, by choosing the correct hand position from 4 pictured examples of arm- hand configurations (see Figure 1). The 4-choice solution contained one correct end position. All other answers were false. The researcher compared the answer given by the participant with the accurate hand position. The explicit motor imagery task consisted of 12 items (6 for the paretic arm and 6 for the nonparetic arm). If all answers were correct, a total maximum score of 12 could be reached. 2.2.4. Utrechtse Arm-Hand Task (UAT). Hand function was measured with the Utrecht Arm-Hand task (UAT) [39]. The UAT consists of a hierarchical ordinal scale, ranging from 0 (nonfunctional arm) to 7 (clumsy arm). 2.2.5. Brunnstro¨m Fugl-Meyer Scale (BFM). The functional level of the patients was measured with the Brunnstro¨m Fugl- Meyer Scale (BFM). This test measures motor recovery in patients with hemiplegia following stroke [40]. The BFM scale includes items related to movements of the shoulder, elbow, forearm, wrist, and hand in the upper extremity, as well as the hip, knee, and ankle in the lower extremity. For the present study, only the upper extremity was measured. Each item was scored on a 3-point ordinal scale (0: cannot perform, 1: performs partially, 2: performs fully). The total score on the upper extremity part of the BFM ranged from 0 (hemiplegia) to a maximum of 66 points (normal motor performance). 2.3. Procedure. To measure the recovery of motor imagery ability and arm-hand function, each patient was assessed 2 times: 3 weeks poststroke and 6 weeks poststroke. During the measurements, all subjects sat at a table in a chair with a backrest. Subjects were instructed to refrain from any actual movements during motor imagery tasks. In between the two measurement sessions the patients continued with their regular treatment program. The control group, who acted as a reference value to determine normal motor imagery ability, was measured once during the research period. 2.4. Statistical Analyses. Group differences between patients and controls on implicit motor (ACC and RT), visual (ACC and RT), and explicit motor imagery 3 weeks poststroke, were determined by a Mann-Whitney U Test with exact P values. Subsequently, a modified t-test [41] with P < .05 was used to compare individual patients’ scores with the control group to determine individual impairment of motor 4 Rehabilitation Research and Practice Table 1: Mean accuracy scores for patients that were impaired on the implicit motor imagery and, or the visual imagery task and, or the explicit motor imagery task versus control subjects (SD in parentheses) at 3 weeks poststroke. Impairment of individual patients versus controls was tested with a modified t-test, with P < .05. Table shows that 7 of the 12 patients were not impaired on any of the imagery tasks. One patient was impaired on the visual imagery task selectively, 2 patients were impaired on implicit motor and visual imagery simultaneously, and 2 patients were impaired on implicit motor imagery selectively. Implicit motor imagery Visual imagery Explicit motor imagery Controls 89.5 (6.8) 90.3 (10.6) 7.5 (2.0) Patients No impairment of imagery 1 96 99 10 4 81 95 8 5 85 94 6 6 83 85 7 8 84 90 8 10 77 73 7 11 83 97 8 Selective impairment of visual imagery 12 73 57 6 Impairment of motor imagery Selectively 3 47 70 6 9 53 93 0 Simultaneous with visual imagery 2 52 56 6 7 57 62 0 imagery. The correlation between mental imagery measures and motor function measures in the patients group was determined by calculating Pearson correlations between all measures on 3 weeks poststroke and by calculating Pearson correlations between all measures on 6 weeks poststroke. To determine whether mental imagery ability and motor function improved at 6 weeks poststroke compared to 3 weeks poststroke, a Wilcoxon Signed-Ranks Test on implicit motor imagery (ACC and RT), visual imagery (ACC and RT), explicit motor imagery, UAT, and BFM was used. All data were analyzed with SPSS version 16.0 (SPSS, Inc., Chicago, IL, USA). 3. Results 3.1. Three Weeks Poststroke 3.1.1. Imagery Ability: Patients versus Controls. Figure 2 shows the mean accuracy scores of the control group compared with the patients group for the implicit motor and the visual imagery task. The Mann-Whitney U Test showed that the patients had a significantly lower implicit motor imagery accuracy score then controls (U = 16.5, P = .003). Visual imagery Imagery accuracy: Patients versus controls 60 70 80 90 100 Implicit motor imagery Patients Controls ∗ C or re ct (% ) Figure 2: Differences between Patients (white bars) and Controls (black bars) on mean implicit motor and visual imagery accuracy. Asterisk indicates significant differences. Patients were less accurate then controls on implicit motor imagery at 3 weeks poststroke (P = .003). The difference between patients and controls on mean visual imagery accuracy was not significant (P = .136). No significant differences existed between the patients and the control group on the visual imagery accuracy score (U = 37, P = .136) and the explicit motor imagery task (U = 46.5, P = .382). The reaction times for the implicit motor imagery task and the visual imagery task did not differ significantly (withU = 48, P = .456, and U = 46, P = .381, resp.). 3.1.2. Imagery Ability: Individual Differences. Comparison of the individual patients’ scores with the control group mean with a modified t-test with (P < .05) showed that one patient had a lower score on visual imagery selectively. Four of the 12 patients scored significantly below mean accuracy of the control group on the implicit motor imagery task. From these 4 patients that were impaired on the implicit motor imagery task, 2 patients also differed significantly from the control group on the visual imagery task and the other 2 patients were selectively impaired on the implicit motor imagery task. Also, 2 patients differed significantly from the control group on the explicit motor imagery task. Patient 9 scored significantly below the mean accuracy of the control group on the implicit motor imagery task and the explicit motor imagery task. Patient 7 scored significantly below the mean accuracy of the control group on all 3 imagery tasks (see Table 1). These results show that 33% of the patients in this study had impaired motor imagery ability and 67% had unimpaired motor imagery. 3.1.3. Correlations between Mental Imagery and Motor Func- tion Measures at 3 Weeks Poststroke. Table 2 shows the correlations between mental imagery and motor function measures. There is a high significant positive correlation between the motor function measures UAT and BFM while Rehabilitation Research and Practice 5 Visual imagery 60 70 80 90 100 Implicit motor imagery ∗ ∗ 3weeks 6weeks C or re ct (% ) Imagery accuracy: 3weeks versus 6weeks post-stroke Figure 3: Difference between 3 weeks (white bars) and 6 weeks (black bars) patients poststroke mean implicit motor and visual imagery accuracy scores. Asterisk indicates significant differences. Patients were more accurate on implicit motor imagery and visual imagery at 6 weeks poststroke compared to 3 weeks poststroke (P < .01). the correlations between the mental imagery measures of implicit motor imagery, visual imagery and explicit motor imagery, and the UAT and BFM are low to moderate and not significant. Furthermore, Table 2 shows a significant strong positive correlation of implicit motor imagery accuracy with visual imagery accuracy and a significant high positive correlation with explicit motor imagery. 3.2. Six Weeks Poststroke 3.2.1. Recovery of Imagery Ability and Motor Function. One patient dropped out after the 3 weeks poststroke measure- ments. At 6 weeks poststroke the 11 remaining patients were more accurate on the