Robot-aided assessment of wrist proprioception in view of robotic rehabilitation

Opening a door or a jar, writing, and squeezing a lemon are actions that need intact wrist function to be correctly performed. Indeed, the wrist is a joint particularly relevant in fine manipulative tasks, during which accuracy of movement and force exertion is mandatory to accomplish the action properly. In this context, a crucial role is played by sensory afferent information, in particular by proprioception, the sense responsible for awareness of human trunk and limb position, movement, force, and sense of effort. Individuals deprived of proprioceptive afferent information still maintain gross motor functions, despite exhibiting significant deficits during fine actions. Since numerous neurological diseases and orthopedic injuries are known to impair sensory functions, in my doctoral research activity I focused on investigating the role of proprioception using robotic methodologies and technologies. Among the advantages brought by robotic technologies, there is increased temporal and spatial accuracy in the assessment, the opportunity to synchronize other devices to broaden the set of available measurements, and the possibility to develop smart algorithms for rehabilitative training purposes. However, a challenge still open in the field is to develop rehabilitative protocols able to maximize the effectiveness of the intervention, minimizing the temporal duration and the effort required. To achieve this goal, we need to deepen our knowledge of human sensorimotor functions, particularly how sensory integration is carried out and how, consequently, motor commands are generated. For these reasons, my first research objective was to investigate how able-bodied subjects exploit both intrinsic and augmented proprioceptive afferent information. Additionally, the second objective of my research work was to investigate the potential of human wrist robotic rehabilitation in two specific clinical populations of subjects, i.e. orthopedic patients and persons with Multiple Sclerosis (MS). Concerning the former, since the knowledge about the potential of robotics in orthopedic rehabilitation was limited, my goal was to compare the effectiveness of traditional wrist rehabilitation with that of a rehabilitative program entirely performed using a robotic device. The MS population, instead, has been extensively studied particularly with regard to the treatment of motor incoordination through upper-limb robotics. In my work, I focused on the impact of adaptive strength training to prevent muscle weakness in MS and increase cross-education, a phenomenon whereby training one limb results in increased strength in the opposite limb. The whole research project involved the use of a wrist manipulandum with three Degrees of Freedom (DoFs) and a range of motion comparable with that of the human wrist. The robot allows either completely active or assisted wrist extension/flexion (EF), radial/ulnar deviation (RUD), pronation/supination (PS), and coordinated rotations involving multiple DoFs. The device is equipped with high-resolution encoders to measure angular displacement along its three DoFs and with motors, to deliver torques to manipulate the wrist joint, compensate for weight and guarantee low inertia. The robot can be synchronized with external devices useful to investigate wrist sensorimotor function, like the electromyographic system to assess muscle activity. The main findings of my research point out that the sensitivity of proprioceptive afferent information can be influenced by both physiological and external factors. In particular, the wrist position sense of able-bodied subjects was found to be symmetric between hands, but anisotropic between different directions in the EF/RUD space. Among the external factors that can influence proprioception, I focused on the effects of short-term dynamic fatigue, which was able to modify the subject's sensitivity not immediately after the end of the task, but some time later (about four minutes). Another factor that I found to affect the human position sense is task learning. By learning, the proprioceptive space could undergo a task-specific recalibration. Conversely, being the only afference to carry information strictly related to the joint space, the proprioceptive feedback turned out to be the crucial source of information for optimally learning a task. These experimental results highlighted the importance of accurately assessing and exploiting the sensory afferents coming from the wrist joints and muscles to improve the (re)learning process. Additionally, protocols of robotic rehabilitation were found to be helpful and versatile tools to explore wrist sensorimotor functions and treat a wide set of different dysfunctions in both orthopedic and neurologic conditions. After a wrist traumatic event, the benefit of wrist robotic therapy was comparable with that of traditional manual therapy, thus confirming the potential of robotic rehabilitation also for this unexplored clinical population. After a 4-week-long training, MS subjects increased the strength of their forearm muscles, in both the trained and untrained limbs. Even though the clinical outcome measures did not reveal a significant improvement, the subjects’ verbal feedback was enthusiastic and satisfied with the impact the trial had had on their lives. Finally, my research work investigated the use of protocols of robotic rehabilitation as helpful and versatile tools to explore wrist sensorimotor functions and treat dysfunctions arising from both orthopedic and neurologic conditions. After a wrist traumatic event, the benefit of wrist robotic therapy was comparable with that of traditional manual therapy, thus confirming the potential of robot-based rehabilitation also for this unexplored clinical population. After a 4-week-long training, MS subjects increased the strength of their forearm muscles, in both the trained and untrained limbs. Even though other clinical measures did not reveal a significant improvement, the subjects’ verbal feedback was enthusiastic and satisfied with the impact the trial had had on their lives

μ-band desynchronization in the contralateral central and central-parietal areas predicts proprioceptive acuity

IntroductionPosition sense, which belongs to the sensory stream called proprioception, is pivotal for proper movement execution. Its comprehensive understanding is needed to fill existing knowledge gaps in human physiology, motor control, neurorehabilitation, and prosthetics. Although numerous studies have focused on different aspects of proprioception in humans, what has not been fully investigated so far are the neural correlates of proprioceptive acuity at the joints.MethodsHere, we implemented a robot-based position sense test to elucidate the correlation between patterns of neural activity and the degree of accuracy and precision exhibited by the subjects. Eighteen healthy participants performed the test, and their electroencephalographic (EEG) activity was analyzed in its μ band (8–12 Hz), as the frequency band related to voluntary movement and somatosensory stimulation.ResultsWe observed a significant positive correlation between the matching error, representing proprioceptive acuity, and the strength of the activation in contralateral hand motor and sensorimotor areas (left central and central-parietal areas). In absence of visual feedback, these same regions of interest (ROIs) presented a higher activation level compared to the association and visual areas. Remarkably, central and central-parietal activation was still observed when visual feedback was added, although a consistent activation in association and visual areas came up.ConclusionSumming up, this study supports the existence of a specific link between the magnitude of activation of motor and sensorimotor areas related to upper limb proprioceptive processing and the proprioceptive acuity at the joints

Realter: An Immersive Simulator to Support Low-Vision Rehabilitation

The project REALTER (wearable egocentric altered reality simulator) exploits immersive technologies and extended reality (XR) environments to support low-vision rehabilitation, by offering an immersive simulator of low-vision conditions. Perceiving and navigating the world as low-vision individuals has the potential of being a useful tool for ophthalmologists and visual rehabilitators to increase empathy with the assisted population and to improve the existing therapeutic techniques. Additionally, by analyzing ocular movements acquired during experimental sessions with healthy-sighted individuals in a condition of simulated low vision, researchers may collect quantitative data to extend the state of the art in understanding the behavioral changes of low-vision persons. The project involved the implementation of an immersive system by using commercial device tools currently available on the market. The hardware consists of an immersive virtual reality (VR) headset with an integrated eye tracker and a pair of external cameras, to provide gaze-contingent altered/extended reality (XR) content by a pass-through modality. The software can realistically simulate several low-vision conditions, such as age-relatedmacular degeneration, glaucoma, and hemianopsia, and simultaneously acquire eye and head movements for data analysis

A new robot-based proprioceptive training algorithm to induce sensorimotor enhancement in the human wrist

Afferent proprioceptive signals, responsible for body awareness, have a crucial role when planning and executing motor tasks. Increasing evidence suggests that proprioceptive sensory training may improve motor performance. Although this topic had been partially investigated, there was a lack of studies involving the wrist joint. Proprioception at the wrist level is particularly relevant to interact with the environment through actions that require an accurate sense of position and motion, and fine haptic perception. In this study, we implemented and tested a robotic training algorithm of human wrist proprioception. The proposed task was a continuous tracking in the workspace identified by flexion-extension and radial-ulnar deviation movements. Healthy subjects were haptically guided towards the target, without any visual feedback of the position of the end- effector. Our results showed that, after the training, participants improved their motor performance in a different tracking task, completely active and with visual feedback Additionally, the training led them to more efficient use of kinesthetic feedback during haptically-guided reaching tasks. Our findings demonstrated that the proposed training algorithm of wrist proprioception induced a task-specific sensorimotor enhancement. From the perspective of a rehabilitative intervention, this robot-based training has the potential to improve motor functions and the quality of life of subjects with sensorimotor deficits