Francesca Marini

Robot-aided developmental assessment of wrist proprioception in children

BackgroundSeveral neurodevelopmental disorders and brain injuries in children have been associated with proprioceptive dysfunction that will negatively affect their movement. Unfortunately, there is lack of reliable and objective clinical examination protocols and our current knowledge of how proprioception evolves in typically developing children is still sparse.MethodsUsing a robotic exoskeleton, we investigated proprioceptive acuity of the wrist in a group of 49 typically developing healthy children (8–15 years), and a group of 40 young adults. Without vision participants performed an ipsilateral wrist joint position matching task that required them to reproduce (match) a previously experienced target position. All three joint degrees-of-freedom of the wrist/hand complex were assessed. Accuracy and precision were evaluated as a measure of proprioceptive acuity. The cross-sectional data indicating the time course of development of acuity were then fitted by four models in order to determine which function best describes developmental changes in proprioception across age.ResultsFirst, the robot-aided assessment proved to be an easy to administer method for objectively measuring proprioceptive acuity in both children and adult populations. Second, proprioceptive acuity continued to develop throughout middle childhood and early adolescence, improving by more than 50% with respect to the youngest group. Adult levels of performance were reached approximately by the age of 12 years. An inverse-root function best described the development of proprioceptive acuity across the age groups. Third, wrist/forearm proprioception is anisotropic across the three DoFs with the Abduction/Adduction exhibiting a higher level of acuity than those of Flexion/extension and Pronation/Supination. This anisotropy did not change across development.ConclusionsProprioceptive development for the wrist continues well into early adolescence. Our normative data obtained trough this novel robot-aided assessment method provide a basis against which proprioceptive function of pediatric population can be compared. This may aid the design of more effective sensorimotor intervention programs.

Robot-Aided Mapping of Wrist Proprioceptive Acuity across a 3D Workspace

Proprioceptive signals from peripheral mechanoreceptors form the basis for bodily perception and are known to be essential for motor control. However we still have an incomplete understanding of how proprioception differs between joints, whether it differs among the various degrees-of-freedom (DoFs) within a particular joint, and how such differences affect motor control and learning. We here introduce a robot-aided method to objectively measure proprioceptive function: specifically, we systematically mapped wrist proprioceptive acuity across the three DoFs of the wrist/hand complex with the aim to characterize the wrist position sense. Thirty healthy young adults performed an ipsilateral active joint position matching task with their dominant wrist using a haptic robotic exoskeleton. Our results indicate that the active wrist position sense acuity is anisotropic across the joint, with the abduction/adduction DoF having the highest acuity (the error of acuity for flexion/extension is 4.64 ± 0.24°; abduction/adduction: 3.68 ± 0.32°; supination/pronation: 5.15 ± 0.37°) and they also revealed that proprioceptive acuity decreases for smaller joint displacements. We believe this knowledge is imperative in a clinical scenario when assessing proprioceptive deficits and for understanding how such sensory deficits relate to observable motor impairments.

Wrist Proprioception: Amplitude or Position Coding?

This work examines physiological mechanisms underlying the position sense of the wrist, namely, the codification of proprioceptive information related to pointing movements of the wrist toward kinesthetic targets. Twenty-four healthy subjects participated to a robot-aided assessment of their wrist proprioceptive acuity to investigate if the sensorimotor transformation involved in matching targets located by proprioceptive receptors relies on amplitude or positional cues. A joint position matching test was performed in order to explore such dichotomy. In this test, the wrist of a blindfolded participant is passively moved by a robotic device to a preset target position and, after a removal movement from this position, the participant has to actively replicate and match it as accurately as possible. The test involved two separate conditions: in the first, the matching movements started from the same initial location; in the second one, the initial location was randomly assigned. Target matching accuracy, precision, and bias in the two conditions were then compared. Overall results showed a consistent higher performance in the former condition than in the latter, thus supporting the hypothesis that the joint position sense is based on vectorial or amplitude coding rather than positional.

Role of Muscle Synergies in Real-Time Classification of Upper Limb Motions using Extreme Learning Machines

BackgroundMyoelectric signals offer significant insights in interpreting the motion intention and extent of effort involved in performing a movement, with application in prostheses, orthosis and exoskeletons. Feature extraction plays a vital role, and follows two approaches: EMG and synergy features. More recently, muscle synergy based features are being increasingly explored, since it simplifies dimensionality of control, and are considered to be more robust to signal variations. Another important aspect in a myoelectrically controlled devices is the learning capability and speed of performance for online decoding. Extreme learning machine (ELM) is a relatively new neural-network based learning algorithm: its performance hasn’t been explored in the context of online control, which is a more reliable measure compared to offline analysis. To this purpose we aim at focusing our investigation on a myoelectric-based interface which is able to identify and online classify, upper limb motions involving shoulder and elbow. The main objective is to compare the performance of the decoder trained using ELM, for two different features: EMG and synergy features.MethodsThe experiments are broadly divided in two phases training/calibration and testing respectively. ELM is used to train the decoder using data acquired during the calibration phase. The performance of the decoder is then tested in online motion control by using a simulated graphical user interface replicating the human limb: subjects are requested to control a virtual arm by using their muscular activity. The decoder performance is quantified using ad-hoc metrics based on the following indicators: motion selection time, motion completion time, and classification accuracy.ResultsPerformance has been evaluated for both offline and online contexts. The offline classification results indicated better performance in the case of EMG features, whereas a better classification accuracy for synergy feature was observed for online decoding. Also the other indicators as motion selection time and motion completion time, showed better trend in the case of synergy than time-domain features.ConclusionThis work demonstrates better robustness of online decoding of upper-limb motions and motor intentions when using synergy feature. Furthermore, we have quantified the performance of the decoder trained using ELM for online control, providing a potential and viable option for real-time myoelectric control in assistive technology.

Robotic assessment of manual asymmetries in unimanual and bimanual wrist joint position sense

Despite being so similar from a biomechanical perspective, the left and the right arms develop with different dexterity and important functional differences. This asymmetry in motor performance, most commonly known as handedness, has been extensively investigated in numerous research. However, whether such a dominance exists in the proprioceptive system remains unclear. To this end, manual asymmetries in proprioceptive sensitivity were examined in fourteen neurologically healthy right-handed individuals, with a unimanual and bimanual robot-aided wrist joint position matching (JPM) task, whereby they are required to replicate a reference wrist angle in the absence of vision. The results did not provide any evidence of manual asymmetries in proprioceptive acuity but some indication of asymmetry was singled out in motor execution, with smoother movement trajectories when the task was performed by the non dominant hand. In contrast, experimental conditions (unimanual vs. bimanual) appeared to influence proprioceptive acuity as well as movement kinematics: in the unimanual condition proprioceptive acuity was higher and more consistent and, despite the fact that movements were found to be faster in the unimanual task, they resulted smoother if performed with two hands at the same time. In sum, our results indicated that while there was a decrement in performance during bimanual tasks, there was no evidence of proprioceptive hand dominance”.

Online modulation of assistance in robot aided wrist rehabilitation a pilot study on a subject affected by dystonia

In the last two decades robot training in neuro-motor rehabilitation was mainly focused on shoulder-elbow movements. Few examples of devices for training coordinated movements of the wrist have been designed and clinically tested. Such movements are crucial for recovering motor competence and carrying out many ADLs (activities of daily life). Moreover, most of the implemented therapeutic approaches for robot therapy uses point-to-point reaching movements which tend to emphasize the pathological tendency of patients to break down goal-directed movements into a number of jerky sub-movements. In order to address this issue we used our wrist robot and implemented a control scheme characterized by an adapting assistance delivered to the subject to promote recovery and teach correct motor coordination between flexion/extension and abduction/adduction of wrist movement while tracking a target. The main purpose was to promote the emergence of smoothness in the motor control patterns and maximize the recovery of the normal RoM (range of motion). A preliminary pilot study is illustrated in this work; a pediatric subject affected by muscular dystonia was enrolled in the experiment and he was asked to participate to three therapy sessions on consecutive days. The implementation of a new adaptive, assistive force controller is discussed in details and results are reported comparing the effect of robotic therapy for both dynamic and kinematic changes at the beginning and end of the experiment.

Robotic techniques for the assessment of proprioceptive deficits and for proprioceptive training

Abstract In spite of the acknowledged importance of proprioception for motor control and neuromotor rehabilitation, no effective method for assessment and rehabilitation of proprioceptive deficits has emerged in clinical practice. While there are many clinical scales for assessing proprioception, they all have insufficient psychometric properties and cannot be used in closed-loop treatment paradigms wherein treatment parameters should be monitored and adjusted online or with a trial-by-trial frequency. Robotic technology can be the answer because it can address at the same time two critical interrelated objectives: to provide sensitive and repeatable assessments of proprioceptive integrity and to automate repetitive training procedures designed to enhance proprioception and its contributions to functional movement.

Quantitative Muscle Fatigue Assessment in Neuromuscular Disorders: A Pilot Study on Duchenne Pediatric Subjects

The assessment of muscle fatigue could provide crucial information to monitor the progression of a neuromuscular disease, as well as evidences about the efficacy of an eventual therapeutic approach. The aim of the present work is to test the feasibility of a novel method based on a robotic wrist device and sEMG, on neuromuscular pediatric subjects for a future implementation in clinical practice. The proposed paradigm has been previously validated on a population of healthy subjects. Five children (age 8.8 ± 1.3 yo) with Duchenne Muscular Dystrophy (DMD) performed the test and their right flexor and extensor carpi radialis were recorded to obtain an objective indicator of muscle fatigue.

Proprioceptive identification of joint position versus kinaesthetic movement reproduction

Regarding our voluntary control of movement, if identification of joint position, that is independent of the starting condition, is stronger than kinaesthetic movement reproduction, that implies knowledge of the starting position and movements length for accuracy, is still a matter of debate in motor control theories and neuroscience. In the present study, we examined the mechanisms that individuals seem to prefer/adopt when they locate spatial positions and code the amplitude of movements. We implemented a joint position matching task on a wrist robotic device: this task consists in replicating (i.e. matching) a reference joint angle in the absence of vision and the proprioceptive acuity is given by the goodness of such matching. Two experiments were carried out by implementing two different versions of the task and performed by two groups of 15 healthy participants. In the first experiment, blindfolded subjects were asked to perform matching movements towards a fixed target position, experienced with passive movements that started from different positions and had different lengths. In the second experiment, blindfolded subjects were requested to accurately match target positions that had a different location in space but were passively shown through movements of the same length. We found a clear evidence for higher performances in terms of accuracy (0.42±0.011/°) and precision (0.43±0.011/°) in the first experiment, therefore in case of matching positions, rather than in the second where accuracy and precision were lower (0.36±0.011/° and 0.35±0.011/° respectively). These results suggested a preference for proprioceptive identification of joint position rather than kinaesthetic movement reproduction.

The Influence of External Forces on Wrist Proprioception

Proprioception combines information from cutaneous, joint, tendon, and muscle receptors for maintaining a reliable internal body image. However, it is still a matter of debate, in both neurophysiology and psychology, to what extent such body image is modified or distorted by a changing haptic environment. In particular, what is worth investigating is the contribution of external forces on our perception of body and joint configuration. The proprioceptive acuity of fifteen young participants was tested with a Joint Position Matching (JPM) task, performed with the dominant wrist under five different external forces, in order to understand to what extent they affect proprioceptive acuity. Results show that accuracy and precision in target matching do not change in a significant manner as a function of the loading condition, suggesting that the multi-sensory integration process is indeed capable of discriminating different sub-modalities of proprioception, namely the joint position sense and the sense of force. Furthermore, results indicate a preference for target undershooting when movements are performed in a viscous or high resistive force field, rather than passive or null fields in which subjects did not show any predominance for under/over estimation of their position.