基于脑卒中后运动康复领域的运动想象的研究

脑卒中后造成的神经性损伤是目前导致患者运动功能性障碍的主要原因之一,为社会和患者家庭造成巨大的精神和经济负担。运动想象易学习、成本低,是辅助脑卒中后患者康复的重要手段之一,对改善患者运动功能障碍、提高生活质量具有重要意义。本文主要总结运动想象对脑卒中后康复的积极作用,概述运动想象的生理表现和理论模式、运动想象能力的影响因素、运动想象能力的评分标准,并分析目前运动想象在辅助脑卒中后患者运动功能的康复治疗过程中存在的实验对象单一、评估方法主观化、实验设备分辨率低等缺陷,希望帮助脑卒中后患者更加科学、有效地使用运动想象疗法。     

Motor planning of arm movements is direction-dependent in the gravity field

In the present study we analyzed kinematic and dynamic features of arm movements in order to better elucidate how the motor system integrates environmental constraints (gravity) into motor planning and control processes. To reach this aim, we experimentally manipulated the mechanical effects of gravity on the arm while maintaining arm inertia constant (i.e. the distribution of the mass around the shoulder joint). Six subjects performed single-joint arm movements (rotation around the shoulder joint) in both sagittal (upward, U, versus downward, D) and horizontal (left, L, versus right, R) planes, at different amplitudes and from different initial positions. Under these conditions, shoulder gravitational torques (SGTs) significantly varied when arm movements were performed in the sagittal but not in the horizontal plane. Contrary to SGTs, arm inertia remained constant and similar for both horizontal and sagittal planes since subjects performed arm movements with only one degree of freedom. All subjects, whatever the movement direction, appropriately scaled shoulder joint kinematic parameters according to movement amplitude. Furthermore, peak velocity and movement duration were equivalent for both horizontal and sagittal planes. Interestingly, some kinematic parameters significantly differed according to U/D but not L/R directions. Specifically, acceleration duration was greater for D than U movements, while the opposite was true for peak acceleration. Consequently, although vertical and horizontal arm movements shared a general common strategy (i.e. scaling law), the kinematic asymmetries between U and D arm movements, especially those that reflect central planning process (i.e. peak acceleration), indicated different motor intentions regarding the direction of the upcoming movement. These findings indicate that the interaction of the arm with the dynamics of the environment is internally represented during the generation of arm trajectories.     

Movement-related potentials associated with movement preparation and motor imagery

Movement-related potentials (MRPs), reflecting cortical activity associated with voluntary movement, typically show a slowly increasing negative potential beginning between 1 and 2 s prior to movement, which most likely reflects motor preparatory processes. Studies of regional cerebral blood flow implicate the supplementary motor area in such preparatory processes; however, the contribution of the supplementary motor area to premovement activity observed in MRPs is debated. It is possible to examine MRPs relating to movement prepa4-ration alone, in the absence of movement execution, by recording MRPs associated with imagined movements. In this study, MRPs were recorded from 11 healthy control subjects while performing a sequential button-pressing task in response to external cues, and while imagining performance of the same task in response to the same cues. The early component of MRPs was found not to differ in amplitude, onset time, or topography when performing compared with imagining movement, indicating that both movement execution and motor imagery involve similar pre-movement preparatory processes generated in the same cortical area — most likely the supplementary motor area. It is therefore concluded that the early component of the MRP reflects activity arising pre-dominantly from the supplementary motor area and is associated with pre-movement motor preparatory processes which occur relatively independently of actual movement execution.     

Neural correlates of motor imagery for elite archers

Motor imagery is a mental rehearsal of simple or complex motor acts without overt body movement. It has been proposed that the association between performance and the mental rehearsal period that precedes the voluntary movement is an important point of difference between highly trained athletes and beginners. We compared the activation maps of elite archers and nonarchers during mental rehearsal of archery to test whether the neural correlates of elite archers were more focused and efficiently organised than those of nonarchers. Brain activation was measured using functional MRI in 18 right‐handed elite archers and 18 right‐handed nonarchers. During the active functional MRI imagery task, the participants were instructed to mentally rehearse their archery shooting from a first‐person perspective. The active imagery condition was tested against the nonmotor imagery task as a control condition. The results showed that the premotor and supplementary motor areas, and the inferior frontal region, basal ganglia and cerebellum, were active in nonarchers, whereas elite archers showed activation primarily in the supplementary motor areas. In particular, our result of higher cerebellar activity in nonarchers indicates the increased participation of the cerebellum in nonarchers when learning an unfamiliar archery task. Therefore, the difference in cerebellar activation between archers and nonarchers provides evidence of the expertise effect in the mental rehearsal of archery. In conclusion, the relative economy in the cortical processes of elite archers could contribute to greater consistency in performing the specific challenge in which they are highly practised. Copyright © 2010 John Wiley & Sons, Ltd.     

Physical practice induces excitability changes in human hand motor area during motor imagery

The present study was undertaken to investigate the effects of physical practice on excitability changes in human primary motor cortex (M1) during motor imagery (MI). Using different intensities of transcranial magnetic stimulation (TMS), we examined changes in the motor evoked potential (MEP) of the first dorsal interosseous (FDI) muscle with and without MI, and before and after physical practice. On comparing results for MEPs recorded before and after physical practice, the difference between the MEP amplitudes observed at rest and during MI only increased at higher TMS intensities. This finding indicates a physical practice-dependent increase of the higher threshold recruitment of corticospinal tract neurons (CTNs), consistent with synchronization for efficient movement, and provides evidence that neural mechanisms of MI depend not only on the type of movement but also on the extent of the motor adaptation (the physical practice). These present findings also show the benefit of MI and highlight beneficial neural mechanisms related to the activation of M1 during MI. In other words, MI may reflect functional changes of M1 that are similar to the changes observed after physical practice.     

The role of motor imagery in learning a totally novel movement

The aim of the present study is to gain more insight into the mechanisms underlying mental practice. The question of whether a totally novel movement may be learned by mental practice was investigated. Healthy young adults had to learn the abduction of the big toe (dominant right foot) without moving the other toes or the foot. The subjects were divided into two groups: subjects who were absolutely unable to abduct their big toe ("absolute zero" group) and subjects who were able to abduct their toe to some extent but showed clear room for improvement ("already doing it" group). Two separate experiments were executed. In the first experiment, 37 absolute-zero subjects had to practice, mentally or physically, the target movement. In the second experiment 40 already-doing-it subjects had to improve their toe-abduction skill. The results showed that absolute-zero subjects could not acquire the toe-abduction movement by means of mental practice. Only subjects who physically practiced the target movement improved significantly. Subjects who had some experience in the task (already-doing-it subjects) improved significantly after mental practice as well as after physical practice. The results seem to indicate that it is more plausible to explain the learning effects of mental practice in terms of a "top-down" mechanism based on the activation of a central representation of the movement than in terms of a peripheral "bottom-up" mechanism based on the activation of muscles.     

Visuo-motor learning with combination of different rates of motor imagery and physical practice

Sports psychology suggests that mental rehearsal facilitates physical practice in athletes and clinical rehabilitation attempts to use mental rehearsal to restore motor function in hemiplegic patients. Our aim was to examine whether mental rehearsal is equivalent to physical learning, and to determine the optimal proportions of real execution and rehearsal. Subjects were asked to grasp an object and insert it into an adapted slot. One group (G0) practiced the task only by physical execution (240 trials); three groups imagined performing the task in different rates of trials (25%, G25; 50%, G50; 75%, G75), and physically executed movements for the remaining trials; a fourth, control group imagined a visual rotation task in 75% of the trials and then performed the same motor task as the others groups. Movement time (MT) was compared for the first and last physical trials, together with other key trials, across groups. All groups learned, suggesting that mental rehearsal is equivalent to physical motor learning. More importantly, when subjects rehearsed the task for large numbers of trials (G50 and G75), the MT of the first executed trial was significantly shorter than the first executed trial in the physical group (G0), indicating that mental practice is better than no practice at all. Comparison of the first executed trial in G25, G50 and G75 with the corresponding trials in G0 (61, 121 and 181 trials), showed equivalence between mental and physical practice. At the end of training, the performance was much better with high rates of mental practice (G50/G75) compared to physical practice alone (G0), especially when the task was difficult. These findings confirm that mental rehearsal can be beneficial for motor learning and suggest that imagery might be used to supplement or partly replace physical practice in clinical rehabilitation.     

Neural activation in cognitive motor processes: comparing motor imagery and observation of gymnastic movements

The simulation concept suggested by Jeannerod (Neuroimage 14:S103-S109, 2001) defines the S-states of action observation and mental simulation of action as action-related mental states lacking overt execution. Within this framework, similarities and neural overlap between S-states and overt execution are interpreted as providing the common basis for the motor representations implemented within the motor system. The present brain imaging study compared activation overlap and differential activation during mental simulation (motor imagery) with that while observing gymnastic movements. The fMRI conjunction analysis revealed overlapping activation for both S-states in primary motor cortex, premotor cortex, and the supplementary motor area as well as in the intraparietal sulcus, cerebellar hemispheres, and parts of the basal ganglia. A direct contrast between the motor imagery and observation conditions revealed stronger activation for imagery in the posterior insula and the anterior cingulate gyrus. The hippocampus, the superior parietal lobe, and the cerebellar areas were differentially activated in the observation condition. In general, these data corroborate the concept of action-related S-states because of the high overlap in core motor as well as in motor-related areas. We argue that differential activity between S-states relates to task-specific and modal information processing.     

Enhancement of spike and wave discharges by GABAmimetic drugs in rats with spontaneous petit-mal-like epilepsy

Certain Wistar rats from our laboratory colony present genetically determined seizures similar to human petit-mal absences. Muscimol, THIP and L-baclofen, agonists of GABA receptors, and gamma-vinyl GABA (GVG), an inhibitor of GABA degradation, enhanced the duration of spontaneous petit-mal-like seizures in a dose-dependent fashion. These findings raise questions as to the role of GABAergic neurotransmission in the occurrence of this type of spontaneous spike and wave discharges.     

基于动态偏定向相干的运动想象因效性网络分析

利用脑网络对脑功能机制和脑认知状态进行基础研究具有重要的意义。本文依据一种测量头皮脑电信号(EEG)的时间-频率域相互作用的方法,即偏定向相干(PDC),提出了动态PDC(dPDC)算法对运动想象的因效性网络建模。研究利用2008年第四届BCI竞赛数据的9个被试计算了不同运动想象任务下因效性网络的参数特征(出入度、集群系数、离心率等),通过显著性检验分析了左、右手运动想象在不同脑区EEG信号的交互影响。结果表明,左右手想象任务的网络集群系数大于随机网络,且特征路径长度与随机网络近似,验证了该网络的小世界特性。对左、右手运动想象的网络特征参数的分析对比,验证了两种任务部分特征具有显著差异,如:针对出度的统计分析表明,在ROI2(P=0.007)和ROI3(P=0.002)区域具有显著差异。基于dPDC算法的因效性网络对运动想象脑区间信息流变化的分析表明,左、右手运动想象的活动区域主要位于左右侧中央前回(ROI2和ROI3)和左右侧中央枕区(ROI5和ROI6)。因此,基于dPDC的因效性网络可以有效表征运动想象的状态,为研究提供了新的手段。     

基于CSP的多类运动想象脑电特征自动选择算法

目的在基于协方差矩阵近似联合对角化(joint approximation diagonalization,JAD)的多类共空间模式(common spatial pattern,CSP)运动想象检测滤波器的设计过程中,需要对关键特征向量进行选择。较常用的基于"最高得分特征值准则"的特征向量选择方法会出现不同类数据的最高得分特征值对应同一个特征向量,因此导致无效CSP滤波器的出现,进而影响系统识别率。本文在传统JAD方法上提出一种特征值自动选择方法以解决特征值选择无效问题。方法基于BCI Competition 2005data IIIa(BCI2005)和实验室自主采集三类运动想象脑电(EEG)数据集,对不同想象类别数据对应同一个特征向量的异常现象进行实验分析。结果在两个数据集自测试下,本方法的三类运动想象平均识别率分别达到82.78%和85.92%,比传统JAD提高3.44%和3.25%。结论基于CSP的多类运动想象脑电特征自动选择算法能够有效解决特征值选择无效问题,进而提升运动想象BCI系统的分类识别率。     

基于Jensen熵的运动想象脑电信号稳态子空间分析

目的虽然稳态子空间分析(stationary subspace analysis,SSA)算法在脑电研究领域取得了一定的成效,但目前该算法还不够完善,脑电数据分类误差还比较大,因此要想更好地研究脑电信号,就必须进一步加强算法优化,减少分类误差。本文提出了一种基于Jensen熵(Jensen-Shannon divergence,JSD)的稳态子空间分析算法,并将改进后的算法应用到二类和四类运动想象脑电信号中。方法将JSD代替原SSA算法中的KL散度(Kullback-Leibler divergence,KLD),对改进后的算法(以下简称为JSSA算法)进行模拟仿真,然后将SSA算法和JSSA算法应用到二类和四类运动想象脑电信号中,对Graz2003和Graz2008数据集进行分类提取,并用t检验方法考量SSA算法和JSSA算法所得到的分类准确率是否有显著提高。结果相比于普通算法,SSA算法可以提高运动想象脑电数据的分类准确率,而且基于JSSA算法比基于SSA算法能使运动想象脑电信号分类效果更加准确。结论基于Jensen熵的运动想象脑电信号稳态子空间分析算法相比于SSA算法准确率更好,从而可以使运动想象脑电分类准确率更高。     

Scaling of the metrics of visually-guided arm movements during motor learning in primates

Summary Hand trajectory, tangential velocity and acceleration, time and distance until peak velocity and reaction time were analyzed during the process of learning a skilled, visually-guided arm movement. Primates were trained to move a cursor with a manipulandum from a start box to target boxes displayed on a horizontal video screen during control conditions and when the relationship (gain) between the cursor and manipulandum was altered. The animals adapted to the altered feedback over 100–200 trials. A subsequent testing phase with randomly interspersed trials using the control gain demonstrated that the animals had modified their movements appropriately for the novel gain. Examination of the kinematics revealed that in adapting to a novel gain, primates scaled movement amplitude, tangential velocity, acceleration, and duration appropriately for the distance the hand needed to travel. Yet time to peak velocity was kept constant. Reaction time also remained unchanged for three of the four animals. Movements were performed in two phases, the first from movement onset to peak velocity and the second from peak velocity until the end of the movement. During the first phase the shape of the trajectory and velocity profile were stereotypic and without evidence of any corrections, consistent with this phase being essentially open loop. However, corrections occurred in the second phase and we propose visual feedback was used to correct for the difference in hand/cursor position. Learning appeared to involve utilizing the errors from previous trials to modify the early feedforward phase of subsequent trials. Peak tangential velocity, total movement duration and distance reached at peak tangential velocity all scaled linearly with the total movement distance required at each gain. Based on regression analyses, for none of these variables were the changes in learning completely adequate to compensate for total distance required. However, distance to peak velocity scaled with peak velocity in relation to the control gain. The results show that non-human primates adopt a consistent strategy when learning to scale a multi-joint movement. The metrics of the movement scaled yet the time to peak velocity remained constant, suggesting independent control of time and amplitude. Keeping time to peak velocity constant as well as the scaling of peak velocity with distance to peak velocity are viewed as ways to simplify the learning process.     

Adaptation and generalization in acceleration-dependent force fields

Any passive rigid inertial object that we hold in our hand, e.g., a tennis racquet, imposes a field of forces on the arm that depends on limb position, velocity, and acceleration. A fundamental characteristic of this field is that the forces due to acceleration and velocity are linearly separable in the intrinsic coordinates of the limb. In order to learn such dynamics with a collection of basis elements, a control system would generalize correctly and therefore perform optimally if the basis elements that were sensitive to limb velocity were not sensitive to acceleration, and vice versa. However, in the mammalian nervous system proprioceptive sensors like muscle spindles encode a nonlinear combination of all components of limb state, with sensitivity to velocity dominating sensitivity to acceleration. Therefore, limb state in the space of proprioception is not linearly separable despite the fact that this separation is a desirable property of control systems that form models of inertial objects. In building internal models of limb dynamics, does the brain use a representation that is optimal for control of inertial objects, or a representation that is closely tied to how peripheral sensors measure limb state? Here we show that in humans, patterns of generalization of reaching movements in acceleration-dependent fields are strongly inconsistent with basis elements that are optimized for control of inertial objects. Unlike a robot controller that models the dynamics of the natural world and represents velocity and acceleration independently, internal models of dynamics that people learn appear to be rooted in the properties of proprioception, nonlinearly responding to the pattern of muscle activation and representing velocity more strongly than acceleration.     

基于时空特征学习卷积神经网络的运动想象脑电解码方法

基于运动想象脑电(EEG)的脑-机接口系统能够为用户提供更为自然、灵活的控制方式,已广泛应用到人机交互领域。然而,由于目前运动想象脑电的信噪比及空间分辨率较低,导致信号解码正确率较低。针对这一问题,本文提出一种基于时空特征学习卷积神经网络(TSCNN)的运动想象脑电解码方法。首先,针对经过带通滤波预处理的脑电信号,依次设计时间和空间维度上的卷积层,构造出运动想象脑电的时空特征;然后,利用2层二维卷积结构对脑电的时空特征进行抽象学习;最后,通过全连接层和Softmax层对TSCNN学习的抽象特征进行解码。利用公开数据集对该方法进行实验测试,结果表明,所提方法的平均解码精度达到80.09%,分别比经典的解码方法共空间模式(CSP)+支持向量机(SVM)和滤波器组CSP(FBCSP)+SVM提高了13.75%和10.99%,显著提升了运动想象脑电解码的可靠性。     

Modulation of EMG power spectrum frequency during motor imagery

To provide evidence that motor imagery (MI) is accompanied by improvement of intramuscular conduction velocity (CV), we investigated surface electromyographic (EMG) activity of 3 muscles during the elbow flexion/extension. Thirty right-handed participants were asked to lift or to imagine lifting a weighted dumbbell under 3 types of muscular contractions, i.e. concentric, isometric and eccentric, taken as independent variables. The EMG activity of the agonist (long and short heads of biceps brachii) and the antagonist (long portion of triceps brachii) muscles was recorded and processed to determine the median frequency (MF) of EMG power spectrum as dependant variable. The MF was significantly higher during the MI sessions than during the resting condition while the participants remained strictly motionless. Moreover, the MF during imagined concentric contraction was significantly higher than during the eccentric. Thus, the MF variation was correlated to the type of contraction the muscle produced. During MI, the EMG patterns corresponding to each type of muscle contraction remained comparable to those observed during actual movement. In conclusion, specific motor programming is hypothesized to be performed as a function of muscle contraction type during MI.     

Modulation of corticospinal excitability and intracortical inhibition during motor imagery is task-dependent

Previous studies have clearly shown that motor imagery modulates corticospinal excitability. However, there is no clear evidence for the modulation of intracortical inhibition (ICI) during imagined task performance. The aim of this study was to use transcranial magnetic stimulation (TMS) to assess changes in corticospinal excitability and ICI during the imagined performance of two types of task. In Experiment 1, eight subjects performed phasic depression of a computer mouse button using the dominant index finger in time with a 1 Hz auditory metronome. Single and paired pulse magnetic stimuli were delivered at rest, and during the on and off phases of actual and imagined task performance. Motor evoked potentials (MEPs) were recorded from FDI and APB. In Experiment 2, eight subjects performed phasic isometric abduction of the dominant thumb in time with a 1 Hz auditory metronome. As before, single and paired pulse magnetic stimuli were delivered at rest, and during the on and off phases of actual and imagined task performance. In both experiments, the conditioning stimulus intensity was set to produce 50% inhibition at rest, to enable both increases and decreases in ICI during task performance to be detected. No significant temporal or spatial modulation of MEP amplitude or ICI was observed in Experiment 1. In contrast, MEP amplitude was significantly greater, and ICI significantly lower during the on phase of imagined task performance in Experiment 2. These results are most likely related to the higher levels of target muscle activation required during actual task performance and the greater anatomical distance between target and control muscles in Experiment 2. These task characteristics may influence the observed degree of corticospinal excitability and ICI modulation.     

Origins and violations of the 2/3 power law in rhythmic three-dimensional arm movements

The 2/3 power law, the nonlinear relationship between tangential velocity and radius of curvature of the end-effector trajectory, is thought to be a fundamental constraint of the central nervous system in the formation of rhythmic endpoint trajectories. However, studies on the 2/3 power law have been confined largely to planar drawing patterns of relatively small size. With the hypothesis that this strategy overlooks nonlinear effects that are constitutive in movement generation, the present experiments tested the validity of the power law in elliptical patterns that were not confined to a planar surface and which were performed by the unconstrained 7-degrees of freedom (DOF) arm, with significant variations in pattern size and workspace orientation. Data were recorded from five human subjects where the seven joint angles and the endpoint trajectories were analyzed. Additionally, an anthropomorphic 7-DOF robot arm served as a "control subject" whose endpoint trajectories were generated on the basis of the human joint angle data, modeled as simple harmonic oscillations. Analyses of the endpoint trajectories demonstrate that the power law is systematically violated with increasing pattern size, in both exponent and the goodness of fit. The origins of these violations can be explained analytically based on smooth, rhythmic trajectory formation and the kinematic structure of the human arm. We conclude that, in unconstrained rhythmic movements, the power law seems to be a by-product of a movement system that favors smooth trajectories, and that it is unlikely to serve as a primary movement-generating principle. Our data rather suggest that subjects employed smooth oscillatory pattern generators in joint space to realize the required movement patterns.     

基于空间频率与时间序列信息的多类运动想象脑电分类

结合共同空间模式（CSP）、离散小波变换（DWT）和长短期记忆网络（LSTM）方法,提出一种基于空间频率与时间序列信息的多类运动想象脑电特征提取方法。首先利用滑动矩形窗获得时间序列脑电信号,并采用DWT从每一段脑电信号提取运动想象脑电相关的子带小波系数,其次将小波系数通过一对多CSP进一步特征提取,得到的特征作为LSTM的输入,然后对LSTM的时间序列输出在时间步上进行平均,最后使用Softmax分类器进行分类。实验结果显示,新算法取得92.23%的准确率,相比CSP特征以及结合频率或时间序列信息的CSP特征有较大提升,表明空间、频率、时间序列信息的互补性和有效性。     

Effect of a fatiguing protocol on motor imagery accuracy

This study was devised to evaluate the influence of muscle fatigue on athletes ability to perform motor imagery. Performance impairment is a consequence of fatigue, but alterations on perception and mental activity may also occur. To test whether peripheral fatigue affects mental processes, ten sports students imagined three consecutive countermovement jumps before and after a fatiguing protocol, through repetition of upright movements, at 70% of maximal voluntary contraction, until exhaustion. Autonomic nervous system responses and imagined movement durations were considered the dependent variables. Actual duration was systematically overestimated during both visual and kinesthetic imagery, but motor imagery duration and autonomic responses were similar without and under fatigue. Results suggest that muscle fatigue, unlike fatigue induced by prolonged exercise, does not elicit mental fatigue and therefore does not alter motor imagery accuracy.