基于有限状态机的智能下肢假肢控制

背景：传统的下肢假肢行走状态改变时膝关节阻尼不能随之改变,假肢跟随性差,变化范围小。 目的：基于有限状态机的智能下肢假肢控制方法,实现假肢侧对健肢侧的实时跟踪和步速跟随。 方法：智能下肢假肢采用带固定式气缸阻尼器的四连杆机构,采用有限状态机的控制方法,感知当前的步态事件,触发步态状态的转变,调整对应的步态模式,得到步态规划的输出动作。 结果与结论：实验结果表明,智能下肢假肢能够进行步速识别和步态识别,控制器输出不同的控制策略,控制步进电机调整膝关节阻尼的大小,假肢侧能够对健肢侧进行实时跟踪和步速跟随。     

Integration of auditory and kinesthetic information in motion: alterations in Parkinson's disease

The main aim in this work was to study the interaction between auditory and kinesthetic stimuli and its influence on motion control. The study was performed on healthy subjects and patients with Parkinson's disease (PD). Thirty-five right-handed volunteers (young, PD, and age-matched healthy participants, and PD-patients) were studied with three different motor tasks (slow cyclic movements, fast cyclic movements, and slow continuous movements) and under the action of kinesthetic stimuli and sounds at different beat rates. The action of kinesthesia was evaluated by comparing real movements with virtual movements (movements imaged but not executed). The fast cyclic task was accelerated by kinesthetic but not by auditory stimuli. The slow cyclic task changed with the beat rate of sounds but not with kinesthetic stimuli. The slow continuous task showed an integrated response to both sensorial modalities. These data show that the influence of the multisensory integration on motion changes with the motor task and that some motor patterns are modulated by the simultaneous action of auditory and kinesthetic information, a cross-modal integration that was different in PD-patients.     

Motor control over the phantom limb in above-elbow amputees and its relationship with phantom limb pain

Recent evidence shows that the primary motor cortex continues to send motor commands when amputees execute phantom movements. These commands are retargeted toward the remaining stump muscles as a result of motor system reorganization. As amputation-induced reorganization in the primary motor cortex has been associated with phantom limb pain we hypothesized that the motor control of the phantom limb would differ between amputees with and without phantom limb pain. Eight above-elbow amputees with or without pain were included in the study. They were asked to produce cyclic movements with their phantom limb (hand, wrist, and elbow movements) while simultaneously reproducing the same movement with the intact limb. The time needed to complete a movement cycle and its amplitude were derived from the kinematics of the intact limb. Electromyographic (EMG) activity from different stump muscles and from the homologous muscles on the intact side was recorded. Different EMG patterns were recorded in the stump muscles depending on the movement produced, showing that different phantom movements are associated with distinct motor commands. Phantom limb pain was associated with some aspects of phantom limb motor control. The time needed to complete a full cycle of a phantom movement was systematically shorter in subjects without phantom limb pain. Also, the amount of EMG modulation recorded in a stump muscle during a phantom hand movement was positively correlated with the intensity of phantom limb pain. Since phantom hand movement–related EMG patterns in above-elbow stump muscles can be considered as a marker of motor system reorganization, this result indirectly supports the hypothesis that amputation-induced plasticity is associated with phantom limb pain severity. The discordance between the (amputated) hand motor command and the feedback from above-elbow muscles might partially explain why subjects exhibiting large EMG modulation during phantom hand movement have more phantom limb pain.     

Similarity in the dynamics of contralateral motor overflow through increasing frequency of movement in a single limb

This study was designed to investigate the effects of increasing movement frequency of a single limb on the degree of similarity and coherence of the motor outflow in the non-active limb. Twelve young adults performed a series of unilateral hand-clapping tasks (horizontal and vertical in 25-s trials) while seated. Individuals began the movements at a frequency of 1 Hz for 5 s and were required to increase the movement frequency so as to reach their maximum movement frequency during the latter parts of the trial. Hand and finger kinematics and surface EMG of each arm were recorded. The results showed a progressive emergence of overflow muscle activity and involuntary motion in the non-active arm as the movement frequency of the unilateral action increased toward the upper frequency limits of voluntary movement. This ceiling occurred within the range of 6–7 Hz. Activity in the non-active limb emerged as the movement frequency requirements increased, irrespective of the direction of motion for the task (vertical, horizontal), hand used (preferred, non-preferred) or the auditory timing stimulus provided (metronome, no-metronome). The dynamics of the motor overflow in the non-active limb exhibited time- and frequency-dependent patterns similar to those of the active arm. Together, these results demonstrate that the high-frequency unilateral movements of one limb drives the emergence of motor outflow to the opposite limb with the motor output dynamics being produced across both limbs being progressively similar as movement speed increases.     

假肢步态实验平台设计

背景：目前对于假肢的评价还停留在主观感受,缺乏一套客观的评价系统,建立模拟人体运动的在线假肢参数检测系统对于假肢性能的评价、假肢研究设计具有重要意义。 目的：实现假肢的多种步态运动,并通过运动学、动力学数据的比对,评价其仿真程度。 方法：根据仿生学原理,将下肢假肢简化成四杆四轴的力学模型,利用采集得到的多种步态模式,驱动下肢假肢运动,并搭建动态力学测试平台,实时测量假肢运动的地面垂直反力和前后剪力。 结果与结论：假肢步态运动,髋膝关节的变化曲线与正常步态数据相一致,而其地面垂直反力与前后剪力也与正常人体相接近。提示假肢步态实验平台模拟了下肢假肢步态运动,并实时采集假肢运动的多项运动学、动力学参数,具备较高的仿真程度。     

Variability in the effector-specific pattern of motor facilitation during the observation of everyday actions: implications for the clinical use of action observation

Action observation is increasingly considered as a rehabilitation tool as it can increase the cortical excitability of muscles involved in the observed movements and therefore produce effector-specific motor facilitation. In order to investigate the action observation mechanisms, simple single joint intransitive movements have commonly been used. Still, how the observation of everyday movements which often are the prime target of rehabilitation affects the observer cortical excitability remains unclear. Using transcranial magnetic stimulations, we aimed at verifying if the observation of everyday movements made by the proximal or distal upper-limb produces effector-specific motor facilitation in proximal (arm) and distal (hand) muscles of healthy subjects. Results suggest that, similar to simple intransitive movements, observation of more complex everyday movements involving mainly the proximal or distal part of upper limb induces different patterns of motor facilitation across upper limb muscles (P=0.02). However, we observed large inter-individual variability in the strength of the effector-specific motor facilitation induced by action observation. Yet, subjects had similar types of response (strong or weak effector-specific effects) when watching proximal or distal movements indicating that the facilitation pattern was highly consistent within subjects (r=0.83–0.88, P<0.001). This suggests that some individuals are better than other at precisely mapping the observed movements on their motor repertoire and that this type of response holds for various types of everyday actions.     

The basis for a prosthetic shoulder analogue and a view of upper limb function

A versatile single-axial exo-skeletal prosthetic ‘shoulder joint’ is described, capable of working with a more or less intact shoulder and shoulder function, or in the absence of either. It makes possible (i) the transmission of the weight of an arm prosthesis, through a functioning shoulder and some kind of ‘waistcoat’, to the trunk. (ii) Utilization of position feedback and eventual muscle power, of a disorganised limb remnant to provide motion. It gives to the prosthesis an extremely useful field of action, throughout which the hand is kept horizontal, and a pattern of motion which fairly simulates the human shoulder.     

Movement interference during action observation as emergent coordination

Previous research has demonstrated that when an actor coordinates with spatially incompatible movements of another individual that motor interference occurs-the rhythmic arm movements of the actor exhibit increased movement variability in the plane orthogonal (non-instructed) to the instructed plane of motion. Here we examine whether this motor contagion reflects not error but the spontaneous recruitment of additional task-specific movement degrees of freedom employed to withstand increasing task difficulty. Participants coordinated congruent and incongruent forearm movements with a confederate moving at a fast, moderate, and slow target frequency. Examining the variability in the non-instructed plane revealed oscillatory non-instructed plane movements that were coordinated with the instructed plane movements of the confederate. The results suggest motor interference during incongruent coordination can be understood as an emergent, task-specific property of the coordination goal.     

Kinematic and dynamic processes for the control of pointing movements in humans revealed by short-term exposure to microgravity

The generation of accurate motor commands requires implicit knowledge of both limb and environmental dynamics. The action of gravity on moving limb segments must be taken into account within the motor command, and may affect the limb trajectory chosen to accomplish a given motor task. Exactly how the CNS deals with these gravitoinertial forces remains an open question. Does the CNS measure gravitational forces directly, or are they accommodated in the motor plan by way of internal models of physical laws? In this study five male subjects participated. We measured kinematic and dynamic parameters of upward and downward arm movements executed at two different speeds, in both normal Earth gravity and in the weightless conditions of parabolic flight. Exposure to microgravity affected velocity profiles for both directions and speeds. The shape of velocity profiles (the ratio of maximum to mean velocity) and movement duration both showed transient perturbations initially in microgravity, but returned to normal gravity values with practice in 0×g. Differences in relative time to peak velocity between upward versus downward movements, persisted for all trial performed in weightlessness. These differences in kinematic profiles and in the torque profiles used to produce them, diminished, however, with practice in 0×g. These findings lead to the conclusion that the CNS explicitly represents gravitational and inertial forces in the internal models used to generate and execute arm movements. Furthermore, the results suggest that the CNS adapts motor plans to novel environments on different time scales; dynamics adapt first to reproduce standard kinematics, and then kinematics patterns are adapted to optimize dynamics.     

Decrease in cortical activation during learning of a multi-joint discrete motor task

Understanding how the brain learns motor skills remains a very challenging task. To elucidate the neural mechanism underlying motor learning, we assessed brain activation changes on a trial-by-trial basis during learning of a multi-joint discrete motor task (kendama task). We used multi-channel near-infrared spectroscopy (NIRS) while simultaneously measuring upper limb movement changes by using a 3D motion capture system. Fourteen right-handed participants performed the task using their right upper limb while sitting a chair. The task involved tossing a ball connected by a string to the kendama stick (picking up movement) and catching the ball in the cup attached to the stick (catching movement). Participants performed a trial every 20 s for 90 trials. We measured the hemodynamic responses [oxygenated hemoglobin (oxy-Hb) and deoxygenated hemoglobin (deoxy-Hb) signals] around the predicted location of the sensorimotor cortices on both hemispheres. Analysis of the NIRS data revealed that the magnitudes of the event-related oxy-Hb responses to each trial decreased significantly as learning progressed. Analysis of movement data revealed that integrated upper limb muscle torques decreased significantly only for the picking up movements as learning progressed, irrespective of the outcome of the trials. In contrast, dispersion of the movement patterns decreased significantly only for the catching movements in the unsuccessful trials. Furthermore, we found significant positive correlations between the changes in the magnitudes of the oxy-Hb responses and those of the integrated upper limb muscle torques during learning. Our results suggest that the decrease in cortical activation in the sensorimotor cortex reflects changes in motor commands during learning of a multi-joint discrete movement.     

The posterior basal diencephalon of rats enhances expression of an activated state.

STUDY OBJECTIVES: Various ablation studies have implicated the posterior basal diencephalon in the promotion of wakefulness. Although many studies have examined the role of this structure in promotion of cortical arousal, few investigations have attempted to examine its importance in regulation of motor activation (behavioral arousal). In the current study, recordings of freely moving decerebrate rats with and without a posterior basal diencephalon were performed. These studies allowed determination of the behavioral states expressed by the preparations and whether removal of the posterior basal diencephalon completely eliminated expression of both activated state with and activated state without limb movements. DESIGN: Muscle activity was recorded from limb and neck muscles. Eye movements and heart rate were also monitored. The percentage of time spent in various behavioral states and the proportion of limb movements expressed in each of these states were determined. MEASUREMENTS AND RESULTS: Rats with an intact posterior basal diencephalon cycled between all behavioral states. However, they spent most of the recording time in an activated state. In contrast, removal of the posterior basal diencephalon produced rats that spent most of the recording period in a quiescent state. Limb movements were expressed mainly by animals with an intact posterior basal diencephalon, and only when these animals were in the activated state. CONCLUSIONS: The results of this study suggest that the posterior basal diencephalon is required for expression of an activated state and specifically provide evidence for a descending projection from this region required for expression of this state and associated motor activation.     

Visual, motor and attentional influences on proprioceptive contributions to perception of hand path rectilinearity during reaching

We examined how proprioceptive contributions to perception of hand path straightness are influenced by visual, motor and attentional sources of performance variability during horizontal planar reaching. Subjects held the handle of a robot that constrained goal-directed movements of the hand to the paths of controlled curvature. Subjects attempted to detect the presence of hand path curvature during both active (subject driven) and passive (robot driven) movements that either required active muscle force production or not. Subjects were less able to discriminate curved from straight paths when actively reaching for a target versus when the robot moved their hand through the same curved paths. This effect was especially evident during robot-driven movements requiring concurrent activation of lengthening but not shortening muscles. Subjects were less likely to report curvature and were more variable in reporting when movements appeared straight in a novel “visual channel” condition previously shown to block adaptive updating of motor commands in response to deviations from a straight-line hand path. Similarly, compromised performance was obtained when subjects simultaneously performed a distracting secondary task (key pressing with the contralateral hand). The effects compounded when these last two treatments were combined. It is concluded that environmental, intrinsic and attentional factors all impact the ability to detect deviations from a rectilinear hand path during goal-directed movement by decreasing proprioceptive contributions to limb state estimation. In contrast, response variability increased only in experimental conditions thought to impose additional attentional demands on the observer. Implications of these results for perception and other sensorimotor behaviors are discussed.     

Kinematics and kinetics of multijoint reaching in nonhuman primates

The present study identifies the mechanics of planar reaching movements performed by monkeys (Macaca mulatta) wearing a robotic exoskeleton. This device maintained the limb in the horizontal plane such that hand motion was generated only by flexor and extensor motions at the shoulder and elbow. The study describes the kinematic and kinetic features of the shoulder, elbow, and hand during reaching movements from a central target to peripheral targets located on the circumference of a circle: the center-out task. While subjects made reaching movements with relatively straight smooth hand paths and little variation in peak hand velocity, there were large variations in joint motion, torque, and power for movements in different spatial directions. Unlike single-joint movements, joint kinematics and kinetics were not tightly coupled for these multijoint movements. For most movements, power generation was predominantly generated at only one of the two joints. The present analysis illustrates the complexities inherent in multijoint movements and forms the basis for understanding strategies used by the motor system to control reaching movements and for interpreting the response of neurons in different brain regions during this task.     

The effects of muscle fatigue and movement height on movement stability and variability

Performing repetitive manual tasks can lead to muscle fatigue, which may induce changes in motor coordination, movement stability, and kinematic variability. In particular, movements performed at or above shoulder height have been associated with increased shoulder injury risk. The purpose of this study was to determine the effects of repetitive motion-induced muscle fatigue on posture and on the variability and stability of upper extremity movements. Ten healthy subjects performed a repetitive task similar to sawing continuously until volitional exhaustion. This task was synchronized with a metronome to control movement timing. Subjects performed the sawing task at shoulder (“High”) and sternum height (“Low”) on two different days. Joint angles and muscle activity were recorded continuously. Local and orbital stability of joint angles, kinematic variability (within subject standard deviations), and peak joint angles were calculated for five bins of data spaced evenly across each trial. Subjects fatigued more quickly when movements were performed at the High height. They also altered their kinematic patterns significantly in response to muscle fatigue. These changes were more pronounced when the task was performed at the High height. Subjects also exhibited increased kinematic variability of their movements post-fatigue. Increases in variability and altered coordination did not lead to greater instability, however. Shoulder movements were more locally stable when the task was performed at the High height. Conversely, shoulder and elbow movements were more orbitally unstable for the High condition. Thus, people adapt their movement strategies in multi-joint redundant tasks and maintain stability in doing so.     

Characteristics of the Performance of a Formed Motor Skill by Rats with Different Motor Preferences

Wistar rats with different motor preferences were used to study performance of a food-procuring skill – extracting food from a narrow horizontal feeder tube. These experiments showed that when the preferred limb was used, left-handed rats performed the task more quickly (including both preliminary movements and the final successful movements) than right-handed rats. Comparison of movement performance times with the preferred and non-preferred limbs showed that the task was performed more quickly using the left paw in both left- and right-handed rats, i.e., independently of whether this was the preferred paw or not. At the final stage of task performance (grasping and extracting the food), the preferred paw was more successful than the non-preferred paw in both right- and left-handed animals. It is suggested that the organization of the overall strategy for performing this complex behavioral task in rats is determined by the functional heterogeneity of the right and left hemispheres of the brain, which is not linked with limb preference. The selected preference is based on the specific motor and precision characteristics of the preferred paw, while the contralateral hemisphere – the left in right-handed animals and the right in left-handed animals – has a special role in mediating these abilities.     

The utilization of visual feedback from peripheral and central vision in the control of direction

Past research has demonstrated that both peripheral and central vision play an important role in the control of movement direction. However, it has been unclear whether the benefits of these sources of information are due to adjustments in the limb trajectory during movement execution (i.e., online) or modification in motor commands prior to movement initiation (i.e., offline). In the present paper, we analyzed the variability in limb trajectories in a directional aiming task to examine the relative contributions of peripheral and central vision in both the planning and execution of movements. The point of gaze was manipulated to vary where in the limb trajectory information was gained from central and peripheral vision. Analysis of the variability in directional error at various stages of the movement revealed that participants utilized information from early in the trajectory during movement execution when it appeared in both peripheral and central visual fields. Information from late in the trajectory was used offline to improve the programming of subsequent movements regardless of where this information was available in the visual field.     

The strategies to regulate and to modulate the propulsive forces during gait initiation in lower limb amputees

We used the framework of motor program adaptability to examine how unilateral above-knee (AK) or below-knee (BK) amputee subjects organize the global and local biomechanical processes of generation of the propulsive forces during gait initiation to overcome the segmental and neuro-muscular asymmetry. The organization of the global biomechanical process refers to the kinematics behavior of the couple center of foot pressure (CoP) and center of mass (CoM); the organization of the local biomechanical process refers to the propulsive forces generated by the prosthetic or intact limb during the anticipatory postural adjustment phase and the step execution phase. Specifically, we examined: i) the strategy to regulate the progression velocity, i.e., to maintain it comparably when the leading limb changed from the prosthetic limb to the intact limb; and ii) the strategy to modulate the progression velocity, i.e., to increase it when gait was initiated with the prosthetic limb vs. intact limb. The kinematics of the CoM and CoP in the amputees showed the same global biomechanical organization that is typically observed in able-bodied subjects, i.e., the production of the forward disequilibrium torque was obtained by a backward shift of the CoP, followed by a forward acceleration of the CoM. However, gait initiation was achieved by using a different local strategy depending on which limb was used to initiate the step. For the regulation of the CoM progression velocity, when the gait was initiated with the intact limb, the slope of the progression velocity during the anticipatory postural adjustment phase (APA) was steeper and lasted longer, the step execution duration was shorter, and the variation of the CoM speed was lower. In other words, to regulate the speed of progression, the amputee subjects controlled the spatial and temporal parameters of the propulsive forces. In the modulation of the CoM progression velocity, when the gait was initiated with the intact limb, the amputees controlled only the intensity of the propulsive forces during both the APA and step execution phases. In contrast, when the gait was initiated with the prosthetic limb, the modulation resulted mainly from the propulsive forces generated during the step execution phase. These different strategies are discussed in terms of the subjects capacity to adapt the motor program for gait initiation to new constraints.An erratum to this article can be found at     

Perceptual influences on Fitts’ law

The linear relationship between movement time (MT) and index of difficulty (ID) for Fitts’ type tasks has proven ubiquitous over the last 50+ years. A reciprocal aiming task (IDs 3, 4.5, 6) was used to determine if an enlarged visual display (visual angle 5.1°, 7.4°, or 13.3°) would alter this relationship. With ID = 6, a condition typically associated with discrete action control, the largest visual display (13.3°) allowed the motor system to exploit features of cyclical action control, e.g., shorter dwell times, more harmonic motion, less time decelerating the limb. The large visual display resulted in a quadratic relationship between MT and ID. For the IDs of 3 and 4.5, the visual displays did not alter the underlying control processes. The results are discussed in terms of the preference of the motor system to assemble movements from harmonic basis functions when salient visual information is provided.     

Shaping appropriate locomotive motor output through interlimb neural pathway within spinal cord in humans

Direct evidence supporting the contribution of upper limb motion on the generation of locomotive motor output in humans is still limited. Here, we aimed to examine the effect of upper limb motion on locomotor-like muscle activities in the lower limb in persons with spinal cord injury (SCI). By imposing passive locomotion-like leg movements, all cervical incomplete (n = 7) and thoracic complete SCI subjects (n = 5) exhibited locomotor-like muscle activity in their paralyzed soleus muscles. Upper limb movements in thoracic complete SCI subjects did not affect the electromyographic (EMG) pattern of the muscle activities. This is quite natural since neural connections in the spinal cord between regions controlling upper and lower limbs were completely lost in these subjects. On the other hand, in cervical incomplete SCI subjects, in whom such neural connections were at least partially preserved, the locomotor-like muscle activity was significantly affected by passively imposed upper limb movements. Specifically, the upper limb movements generally increased the soleus EMG activity during the backward swing phase, which corresponds to the stance phase in normal gait. Although some subjects showed a reduction of the EMG magnitude when arm motion was imposed, this was still consistent with locomotor-like motor output because the reduction of the EMG occurred during the forward swing phase corresponding to the swing phase. The present results indicate that the neural signal induced by the upper limb movements contributes not merely to enhance but also to shape the lower limb locomotive motor output, possibly through interlimb neural pathways. Such neural interaction between upper and lower limb motions could be an underlying neural mechanism of human bipedal locomotion.     

Control of movement variability and the regulation of limb impedance

Humans routinely make movements to targets that have different accuracy requirements in different directions. Examples extend from everyday occurrences such as grasping the handle of a coffee cup to the more refined instance of a surgeon positioning a scalpel. The attainment of accuracy in situations such as these might be related to the nervous system's capacity to regulate the limb's resistance to displacement, or impedance. To test this idea, subjects made movements from random starting locations to targets that had shape-dependent accuracy requirements. We used a robotic device to assess both limb impedance and patterns of movement variability just as the subject reached the target. We show that impedance increases in directions where required accuracy is high. Independent of target shape, patterns of limb stiffness are seen to predict spatial patterns of movement variability. The nervous system is thus seen to modulate limb impedance in entirely predictable environments to aid in the attainment of reaching accuracy.