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

Neural correlates of bilateral proprioception and adaptation with training

Bilateral proprioception includes the ability to sense the position and motion of one hand relative to the other, without looking. This sensory ability allows us to perform daily activities seamlessly, and its impairment is observed in various neurological disorders such as cerebral palsy and stroke. It can undergo experience-dependent plasticity, as seen in trained piano players. If its neural correlates were better understood, it would provide a useful assay and target for neurorehabilitation for people with impaired proprioception. We designed a non-invasive electroencephalography-based paradigm to assess the neural features relevant to proprioception, especially focusing on bilateral proprioception, i.e., assessing the limb distance from the body with the other limb. We compared it with a movement-only task, with and without the visibility of the target hand. Additionally, we explored proprioceptive accuracy during the tasks. We tested eleven Controls and nine Skilled musicians to assess whether sensorimotor event-related spectral perturbations in μ (8-12Hz) and low-β (12-18Hz) rhythms differ in people with musical instrument training, which intrinsically involves a bilateral proprioceptive component, or when new sensor modalities are added to the task. The Skilled group showed significantly reduced μ and low-β suppression in bilateral tasks compared to movement-only, a significative difference relative to Controls. This may be explained by reduced top-down control due to intensive training, despite this, proprioceptive errors were not smaller for this group. Target visibility significantly reduced proprioceptive error in Controls, while no change was observed in the Skilled group. During visual tasks, Controls exhibited significant μ and low-β power reversals, with significant differences relative to proprioceptive-only tasks compared to the Skilled group-possibly due to reduced uncertainty and top-down control. These results provide support for sensorimotor μ and low-β suppression as potential neuromarkers for assessing proprioceptive ability. The identification of these features is significant as they could be used to quantify altered proprioceptive neural processing in skill and movement disorders. This in turn can be useful as an assay for pre and post sensory-motor intervention research.

Multi-joint Assessment of Proprioception Impairments Poststroke

OBJECTIVES

To investigate shoulder, elbow and wrist proprioception impairment poststroke.

DESIGN

Proprioceptive acuity in terms of the threshold detection to passive motion at the shoulder, elbow and wrist joints was evaluated using an exoskeleton robot to the individual joints slowly in either inward or outward direction.

SETTING

A university research laboratory.

PARTICIPANTS

Seventeen stroke survivors and 17 healthy controls (N=34). Inclusion criteria of stroke survivors were (1) a single stroke; (2) stroke duration <1 year; and (3) cognitive ability to follow simple instructions.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Threshold detection to passive motion and detection error at the shoulder, elbow and wrist.

RESULTS

There was significant impairment of proprioceptive acuity in stroke survivors as compared to healthy group at all 3 joints and in both the inward (shoulder horizontal adduction, elbow and wrist flexion, P<.01) and outward (P<.01) motion. Furthermore, the distal wrist joint showed more severe impairment in proprioception than the proximal shoulder and elbow joints poststroke (P<.01) in inward motion. Stroke survivors showed significantly larger detection error in identifying the individual joint in motion (P<.01) and the movement direction (P<.01) as compared to the healthy group. There were significant correlations among the proprioception acuity across the shoulder, elbow and wrist joints and 2 movement directions poststroke.

CONCLUSIONS

There were significant proprioceptive sensory impairments across the shoulder, elbow and wrist joints poststroke, especially at the distal wrist joint. Accurate evaluations of multi-joint proprioception deficit may help guide more focused rehabilitation.

Grip force makes wrist joint position sense worse

Background

The purpose of this study was to investigate how grip force affects wrist joint position sense.

Methods

Twenty-two healthy participants (11 men and 11 women) underwent an ipsilateral wrist joint reposition test at 2 distinct grip forces [0 and 15% of maximal voluntary isometric contraction (MVIC)] and 6 different wrist positions (pronation 24°, supination 24°, radial deviation 16°, ulnar deviation 16°, extension 32°, and flexion 32°).

Results

The findings demonstrated significantly elevated absolute error values at 15% MVIC (3.8 ± 0.3°) than at 0% MVIC grip force [3.1 ± 0.2°, t(20) = 2.303, P = 0.032].

Conclusion

These findings demonstrated that there was significantly worse proprioceptive accuracy at 15% MVIC than at 0% MVIC grip force. These results may contribute to a better comprehension of the mechanisms underlying wrist joint injuries, the development of preventative measures to lower the risk of injuries, and the best possible design of engineering or rehabilitation devices.

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

Introduction

Position 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.

Methods

Here, 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.

Results

We 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.

Conclusion

Summing 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.

Typical Development of Finger Position Sense From Late Childhood to Adolescence

Finger position sense is a proprioceptive modality highly important for fine motor control. Its developmental time course is largely unknown. This cross-sectional study examined its typical development in 138 children (8-17 years) and a group of 14 healthy young adults using a fast and novel psychophysical test that yielded objective measures of position sense acuity. Participants placed their hands underneath a computer tablet and judged the perceived position of their unseen index finger relative to two visible areas displayed on a tablet following a two-forced-choice paradigm. Responses were fitted to a psychometric acuity function from which the difference between the point-of-subjective-equality and the veridical finger position (ΔPSE) was derived as a measure of position sense bias, and the uncertainty area (UA) as a measure of precision. The main results are: First, children under 12 exhibited a significantly greater UA than adults while adolescent children (13-17 years) exhibited no significant differences when compared to adults. Second, no significant age-related differences in ΔPSE were found across the age range of 8-17 years. This implies that the typical development of finger position sense from late childhood to adulthood is characterized as an age-dependent increase in proprioceptive precision and not as a decrease in bias.

Influence of Neck Pain, Cervical Extensor Muscle Fatigue, and Manual Therapy on Wrist Proprioception

OBJECTIVE

The purpose of this study was to examine the effects of submaximal isometric neck muscle fatigue and manual therapy on wrist joint position sense (JPS) within healthy individuals and individuals with subclinical neck pain (SCNP).

METHODS

Twelve healthy participants and 12 participants with SCNP were recruited. Each group completed 2 sessions, with 48 hours between sessions. On day 1, both groups performed 2 wrist JPS tests using a robotic device. The tests were separated by a submaximal isometric fatigue protocol for the cervical extensor muscles (CEM). On day 2, both groups performed a wrist JPS test, followed by a cervical treatment consisting of manual therapy (SCNP) or neck rest (20 minutes, control group) and another wrist JPS test. Joint position sense was measured as the participant's ability to recreate a previously presented wrist angle. Each wrist JPS test included 12 targets, 6 into wrist flexion and 6 into wrist extension. Kinematic data from the robot established absolute, variability, and constant error.

RESULTS

Absolute error significantly decreased (P = .01) from baseline to post-fatigue in the SCNP group (baseline = 4.48 ± 1.58°; post-fatigue = 3.90 ± 1.45°) and increased in the control group (baseline = 3.12 ± 0.98°; post-fatigue = 3.81 ± 0.90°). The single session of manual cervical treatment significantly decreased absolute error in participants with SCNP (P = .004).

CONCLUSION

This study demonstrated that neck pain or fatigue can lead to altered afferent input to the central nervous system and can affect wrist JPS. Our findings demonstrate that acute wrist proprioception may be improved in individuals with SCNP by a single cervical manual therapy session.

Efficacy of wrist robot-aided orthopedic rehabilitation: a randomized controlled trial

Background

In recent years, many studies focused on the use of robotic devices for both the assessment and the neuro-motor reeducation of upper limb in subjects after stroke, spinal cord injuries or affected by neurological disorders. Contrarily, it is still hard to find examples of robot-aided assessment and rehabilitation after traumatic injuries in the orthopedic field. However, those benefits related to the use of robotic devices are expected also in orthopedic functional reeducation.

Methods

After a wrist injury occurred at their workplace, wrist functionality of twenty-three subjects was evaluated through a robot-based assessment and clinical measures (Patient Rated Wrist Evaluation, Jebsen-Taylor and Jamar Test), before and after a 3-week long rehabilitative treatment. Subjects were randomized in two groups: while the control group (n = 13) underwent a traditional rehabilitative protocol, the experimental group (n = 10) was treated replacing traditional exercises with robot-aided ones.

Results

Functionality, assessed through the function subscale of PRWE scale, improved in both groups (experimental p = 0.016; control p < 0.001) and was comparable between groups, both pre (U = 45.5, p = 0.355) and post (U = 47, p = 0.597) treatment. Additionally, even though groups’ performance during the robotic assessment was comparable before the treatment (U = 36, p = 0.077), after rehabilitation the experimental group presented better results than the control one (U = 26, p = 0.015).

Conclusions

This work can be considered a starting point for introducing the use of robotic devices in the orthopedic field. The robot-aided rehabilitative treatment was effective and comparable to the traditional one. Preserving efficacy and safety conditions, a systematic use of these devices could lead to decrease human therapists’ effort, increase repeatability and accuracy of assessments, and promote subject’s engagement and voluntary participation. Trial Registration ClinicalTrial.gov ID: NCT04739644. Registered on February 4, 2021—Retrospectively registered, https://www.clinicaltrials.gov/ct2/show/study/NCT04739644.

Wrist Position Sense in Two Dimensions: Between-Hand Symmetry and Anisotropic Accuracy Across the Space

A deep investigation of proprioceptive processes is necessary to understand the relationship between sensory afferent inputs and motor outcomes. In this work, we investigate whether and how perception of wrist position is influenced by the direction along which the movement occurs. Most previous studies have tested Joint Position Sense (JPS) through 1 degree of freedom (DoF) wrist movements, such as flexion/extension (FE) or radial/ulnar deviation (RUD). However, the wrist joint has 3-DoF and many activities of daily living produce combined movements, requiring at least 2-DoF wrist coordination. For this reason, in this study, target positions involved movement directions that combined wrist flexion or extension with radial or ulnar deviation. The chosen task was a robot-aided Joint Position Matching (JPM), in which blindfolded participants actively reproduced a previously passively assumed target joint configuration. The JPM performance of 20 healthy participants was quantified through measures of accuracy and precision, in terms of both perceived target direction and distance along each direction of movement. Twelve different directions of movement were selected and both hands tested. The left and right hand led to comparable results, both target extents and directions were differently perceived according to the target direction on the FE/RUD space. Moreover, during 2-DoF combined movements, subjects' perception of directions was impaired when compared to 1-DoF target movements. In summary, our results showed that human perception of wrist position on the FE/RUD space is symmetric between hands but not isotropic among movement directions.

Teleoperation of an Ankle-Foot Prosthesis With a Wrist Exoskeleton

OBJECTIVE

We aimed to develop a system for people with amputation that non-invasively restores missing control and sensory information for an ankle-foot prosthesis.

METHODS

In our approach, a wrist exoskeleton allows people with amputation to control and receive feedback from their prosthetic ankle via teleoperation. We implemented two control schemes: position control with haptic feedback of ankle torque at the wrist; and torque control that allows the user to modify a baseline torque profile by moving their wrist against a virtual spring. We measured tracking error and frequency response for the ankle-foot prosthesis and the wrist exoskeleton. To demonstrate feasibility and evaluate system performance, we conducted an experiment in which one participant with a transtibial amputation tracked desired wrist trajectories during walking, while we measured wrist and ankle response.

RESULTS

Benchtop testing demonstrated that for relevant walking frequencies, system error was below human perceptual error. During the walking experiment, the participant was able to voluntarily follow different wrist trajectories with an average RMS error of 1.55 ^° after training. The ankle was also able to track desired trajectories below human perceptual error for both position control (RMSE = 0.8 ^°) and torque control (RMSE = 8.4%).

CONCLUSION

We present a system that allows a user with amputation to control an ankle-foot prosthesis and receive feedback about its state using a wrist exoskeleton, with accuracy comparable to biological neuromotor control.

SIGNIFICANCE

This bilateral teleoperation system enables novel prosthesis control and feedback strategies that could improve prosthesis control and aid motor learning.

Three-Dimensional Assessment of Upper Limb Proprioception via a Wearable Exoskeleton

Proprioception—the sense of body segment’s position and movement—plays a crucial role in human motor control, integrating the sensory information necessary for the correct execution of daily life activities. Despite scientific evidence recognizes that several neurological diseases hamper proprioceptive encoding with consequent inability to correctly perform movements, proprioceptive assessment in clinical settings is still limited to standard scales. Literature on physiology of upper limb’s proprioception is mainly focused on experimental approaches involving planar setups, while the present work provides a novel paradigm for assessing proprioception during single—and multi-joint matching tasks in a three-dimensional workspace. To such extent, a six-degrees of freedom exoskeleton, ALEx-RS (Arm Light Exoskeleton Rehab Station), was used to evaluate 18 healthy subjects’ abilities in matching proprioceptive targets during combined single and multi-joint arm’s movements: shoulder abduction/adduction, shoulder flexion/extension, and elbow flexion/extension. Results provided evidence that proprioceptive abilities depend on the number of joints simultaneously involved in the task and on their anatomical location, since muscle spindles work along their preferred direction, modulating the streaming of sensory information accordingly. These findings suggest solutions for clinical sensorimotor evaluation after neurological disease, where assessing proprioceptive deficits can improve the recovery path and complement the rehabilitation outcomes.

Robotic Assessment of Wrist Proprioception During Kinaesthetic Perturbations: A Neuroergonomic Approach

Position sense refers to an aspect of proprioception crucial for motor control and learning. The onset of neurological diseases can damage such sensory afference, with consequent motor disorders dramatically reducing the associated recovery process. In regular clinical practice, assessment of proprioceptive deficits is run by means of clinical scales which do not provide quantitative measurements. However, existing robotic solutions usually do not involve multi-joint movements but are mostly applied to a single proximal or distal joint. The present work provides a testing paradigm for assessing proprioception during coordinated multi-joint distal movements and in presence of kinaesthetic perturbations: we evaluated healthy subjects' ability to match proprioceptive targets along two of the three wrist's degrees of freedom, flexion/extension and abduction/adduction. By introducing rotations along the pronation/supination axis not involved in the matching task, we tested two experimental conditions, which differed in terms of the temporal imposition of the external perturbation: in the first one, the disturbance was provided after the presentation of the proprioceptive target, while in the second one, the rotation of the pronation/ supination axis was imposed during the proprioceptive target presentation. We investigated if (i) the amplitude of the perturbation along the pronation/supination would lead to proprioceptive miscalibration; (ii) the encoding of proprioceptive target, would be influenced by the presentation sequence between the target itself and the rotational disturbance. Eighteen participants were tested by means of a haptic neuroergonomic wrist device: our findings provided evidence that the order of disturbance presentation does not alter proprioceptive acuity. Yet, a further effect has been noticed: proprioception is highly anisotropic and dependent on perturbation amplitude. Unexpectedly, the configuration of the forearm highly influences sensory feedbacks, and significantly alters subjects' performance in matching the proprioceptive targets, defining portions of the wrist workspace where kinaesthetic and proprioceptive acuity are more sensitive. This finding may suggest solutions and applications in multiple fields: from general haptics where, knowing how wrist configuration influences proprioception, might suggest new neuroergonomic solutions in device design, to clinical evaluation after neurological damage, where accurately assessing proprioceptive deficits can dramatically complement regular therapy for a better prediction of the recovery path.

Upper Limb Proprioceptive Acuity Assessment Based on Three-Dimensional Position Measurement Systems

The aim of the current work was to verify three-dimensional directional effects on the reproduction error precision of the human upper limb position. Thirty male subjects without history of upper limb pathology were recruited from Renmin University of China. A three-dimensional position reproduction task in six directions (up, down, left, right, far, and near) was performed by each subject. The results suggested that the proprioceptive sense of upper limb position depends on the direction, with smaller absolute errors in Directions 4 (right) and 5 (far) than in Directions 1 (up), 2 (down), 3 (left), and 6 (near). Proprioception near the end of the elbow joint range of motion may be more reliable and sensitive. Subjects reproduced fewer ranges in the horizontal plane (Directions 3, 5, and 6) and they overshot the target position along the z-axis (vertical direction) except for Direction 6. Overestimations of position in the z-axis may be caused by overestimations of force.

Neural correlates of proprioceptive upper limb position matching

Proprioceptive information allows humans to perform smooth coordinated movements by constantly updating one's mind with knowledge of the position of one's limbs in space. How this information is combined with other sensory modalities and centrally processed to form conscious perceptions of limb position remains relatively unknown. What has proven even more elusive is pinpointing the contribution of proprioception in cortical activity related to motion. This study addresses these gaps by examining electrocortical dynamics while participants performed an upper limb position matching task in two conditions, namely with proprioceptive feedback or with both visual and proprioceptive feedback. Specifically, we evaluated the reduction of the electroencephalographic power (desynchronization) in the μ frequency band (8-12 Hz), which is known to characterize the neural activation associated with motor control and behavior. We observed a stronger desynchronization in the left motor and somatosensory areas, contralateral to the moving limb while, parietal and occipital regions, identifying association and visual areas, respectively, exhibited a similar activation level in the two hemispheres. Pertaining to the influence of the two experimental conditions it affected only movement's offset, and precisely we found that when matching movements are performed relying only on proprioceptive information, a lower cortical activity is entailed. This effect was strongest in the visual and association areas, while there was a minor effect in the hand motor and somatosensory areas.

Age-related Declines in Sensorimotor Proficiency are Specific to the Tested Motor Skill Component

This study utilized a 3-degree of freedom robotic device (Wristbot) to examine wrist proprioception and eye-hand coordination in a cross-sectional sample of sixty-three young adults (19-29 years), 20 older young adults (30-49), and 17 older adults (50 years and older). Results indicated differences in the emergence of age-related declines in sensorimotor functioning depending on the tested motor skill component. While young adults exhibited smaller matching error and lower variability compared to older young adults and older adults on the proprioception task, we observed lower times-on-target and higher Linearity indices for participants older than 50 years of age compared to both young adults and older young adults. The present results provide necessary quantitative information on sensorimotor function in adulthood, and have implications for the early diagnosis and effective management of sensorimotor dysfunction in clinical settings using a commercially available robotic device.

Movement related activity in the μ band of the human EEG during a robot-based proprioceptive task

Innovative research in the fields of prosthetic, neurorehabilitation, motor control and human physiology has been focusing on the study of proprioception, the sense through which we perceive the position and movement of our body, and great achievements have been obtained regarding its assessment and characterization. However, how proprioceptive signals are combined with other sensory modalities and processed by the central nervous system to form a conscious body image, is still unknown. Such a crucial question was addressed in this study, which involved 23 healthy subjects, by combining a robot-based proprioceptive test with a specific analysis of electroencephalographic activity (EEG) in the $\mu$ frequency band (8-12 Hz). We observed important activation in the motor area contralateral to the moving hand, and besides, a substantial bias in brain activation and proprioceptive acuity when visual feedback was provided in addition to the proprioceptive information during movement execution. In details, brain activation and proprioceptive acuity were both higher in case of movements performed with visual feedback. Remarkably, we also found a correlation between the level of activation in the brain motor area contralateral to the moving hand and the value of proprioceptive acuity.

Muscle fatigue assessment during robot-mediated movements

BACKGROUND

Several neuromuscular disorders present muscle fatigue as a typical symptom. Therefore, a reliable method of fatigue assessment may be crucial for understanding how specific disease features evolve over time and for developing effective rehabilitation strategies. Unfortunately, despite its importance, a standardized, reliable and objective method for fatigue measurement is lacking in clinical practice and this work investigates a practical solution.

METHODS

40 healthy young adults performed a haptic reaching task, while holding a robotic manipulandum. Subjects were required to perform wrist flexion and extension movements in a resistive visco-elastic force field, as many times as possible, until the measured muscles (mainly flexor and extensor carpi radialis) exhibited signs of fatigue. In order to analyze the behavior and the characteristics of the two muscles, subjects were divided into two groups: in the first group, the resistive force was applied by the robot only during flexion movements, whereas, in the second group, the force was applied only during extension movements. Surface electromyographic signals (sEMG) of both flexor and extensor carpi radialis were acquired. A novel indicator to define the Onset of Fatigue (OF) was proposed and evaluated from the Mean Frequency of the sEMG signal. Furthermore, as measure of the subjects' effort throughout the task, the energy consumption was estimated.

RESULTS

From the beginning to the end of the task, as expected, all the subjects showed a decrement in Mean Frequency of the muscle involved in movements resisting the force. For the OF indicator, subjects were consistent in terms of timing of fatigue; moreover, extensor and flexor muscles presented similar OF times. The metabolic analysis showed a very low level of energy consumption and, from the behavioral point of view, the test was well tolerated by the subjects.

CONCLUSION

The robot-aided assessment test proposed in this study, proved to be an easy to administer, fast and reliable method for objectively measuring muscular fatigue in a healthy population. This work developed a framework for an evaluation that can be deployed in a clinical practice with patients presenting neuromuscular disorders. Considering the low metabolic demand, the requested effort would likely be well tolerated by clinical populations.

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 movement's 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.

Perception of Arm Position in Three-Dimensional Space

Proprioception refers to the senses of body position, movement, force and effort. Previous studies have demonstrated workspace and direction-dependent differences in arm proprioceptive sensitivity within the horizontal plane. In addition, studies of reaching in the vertical plane have shown that proprioception plays a key role in anticipating arm configuration dependent effects of gravity. This suggests that proprioceptive sensitivity could vary with the direction of arm displacement relative to the gravitational vector, as well as with arm configuration. To test these hypotheses, and to characterize proprioception more generally, we assessed the direction-dependence and arm postural-dependence of proprioceptive sensitivity in 3D space using a novel robotic paradigm. A subject’s right arm was coupled to a 7-df robot through a trough that stabilized the wrist and forearm, allowing for changes in configuration largely at the elbow and shoulder. Sensitivity was evaluated using a “same-different” task, where the subject’s hand was moved 1–4 cm away from an initial “test” position to a 2nd “judgment” position. The proportion of trials where subjects responded “different” when the positions were different (“hit rate”), and where they responded “different” when the positions were the same, (“false alarm rate”), were used to calculate d’, a measure of sensitivity derived from signal detection theory (SDT). Initially, a single initial arm posture was used and displacements were performed in six directions: upward, downward, forward, backward, leftward and rightward of the test position. In a follow-up experiment, data were obtained for four directions and two initial arm postures. As expected, sensitivity (d’) increased monotonically with distance for all six directions. Sensitivity also varied between directions, particularly at position differences of 2 and 3 cm. Overall, sensitivity reached near maximal values in this task at 2 cm for the leftward/rightward directions, 3 cm for upward/forward and 4 cm for the downward/backward directions. In addition, when data were grouped together for opposing directions, sensitivity showed a dependence upon arm posture. These data suggest arm proprioceptive sensitivity is both anisotropic in 3D space and configuration-dependent, which has important implications for sensorimotor control of the arm and human-robot interactions.

Tactile-STAR: A Novel Tactile STimulator And Recorder System for Evaluating and Improving Tactile Perception

Many neurological diseases impair the motor and somatosensory systems. While several different technologies are used in clinical practice to assess and improve motor functions, somatosensation is evaluated subjectively with qualitative clinical scales. Treatment of somatosensory deficits has received limited attention. To bridge the gap between the assessment and training of motor vs. somatosensory abilities, we designed, developed, and tested a novel, low-cost, two-component (bimanual) mechatronic system targeting tactile somatosensation: the Tactile-STAR-a tactile stimulator and recorder. The stimulator is an actuated pantograph structure driven by two servomotors, with an end-effector covered by a rubber material that can apply two different types of skin stimulation: brush and stretch. The stimulator has a modular design, and can be used to test the tactile perception in different parts of the body such as the hand, arm, leg, big toe, etc. The recorder is a passive pantograph that can measure hand motion using two potentiometers. The recorder can serve multiple purposes: participants can move its handle to match the direction and amplitude of the tactile stimulator, or they can use it as a master manipulator to control the tactile stimulator as a slave. Our ultimate goal is to assess and affect tactile acuity and somatosensory deficits. To demonstrate the feasibility of our novel system, we tested the Tactile-STAR with 16 healthy individuals and with three stroke survivors using the skin-brush stimulation. We verified that the system enables the mapping of tactile perception on the hand in both populations. We also tested the extent to which 30 min of training in healthy individuals led to an improvement of tactile perception. The results provide a first demonstration of the ability of this new system to characterize tactile perception in healthy individuals, as well as a quantification of the magnitude and pattern of tactile impairment in a small cohort of stroke survivors. The finding that short-term training with Tactile-STAR can improve the acuity of tactile perception in healthy individuals suggests that Tactile-STAR may have utility as a therapeutic intervention for somatosensory deficits.

Codification mechanisms of wrist position sense

Proprioceptive signals from cutaneous, joint, tendon and muscle receptors create the basis for bodily perception and are known to be essential for motor control. However, which are the mechanisms underlying the proprioceptive signals and which are the variables that affect them is still a matter of debate. In particular, what is worth to investigate is, namely, the codification of proprioceptive information related to pointing movements of the wrist towards kinesthetic targets. In this work we asked 10 healthy adults to perform with their wrist a robot-aided proprioceptive matching task, in which the starting position of the matching movements was shifted forward or backward, in order to ascertain to which extent such shifts cause target over/under estimation and how important is movement's length on task performance. Results indicate that accuracy and precision of performance are highly correlated with the starting position and targets tended to be undershot when the active matching movements were longer. Moreover, further analysis revealed a consistent decrement of movement speed for shorter movements and conversely, faster displacement in case of backward of starting position.

Proprioceptive assessment in clinical settings: Evaluation of joint position sense in upper limb post-stroke using a robotic manipulator

Proprioception is a critical component for motor functions and directly affects motor learning after neurological injuries. Conventional methods for its assessment are generally ordinal in nature and hence lack sensitivity. Robotic devices designed to promote sensorimotor learning can potentially provide quantitative precise, accurate, and reliable assessments of sensory impairments. In this paper, we investigate the clinical applicability and validity of using a planar 2 degrees of freedom robot to quantitatively assess proprioceptive deficits in post-stroke participants. Nine stroke survivors and nine healthy subjects participated in the study. Participants’ hand was passively moved to the target position guided by the H-Man robot (Criterion movement) and were asked to indicate during a second passive movement towards the same target (Matching movement) when they felt that they matched the target position. The assessment was carried out on a planar surface for movements in the forward and oblique directions in the contralateral and ipsilateral sides of the tested arm. The matching performance was evaluated in terms of error magnitude (absolute and signed) and its variability. Stroke patients showed higher variability in the estimation of the target position compared to the healthy participants. Further, an effect of target was found, with lower absolute errors in the contralateral side. Pairwise comparison between individual stroke participant and control participants showed significant proprioceptive deficits in two patients. The proposed assessment of passive joint position sense was inherently simple and all participants, regardless of motor impairment level, could complete it in less than 10 minutes. Therefore, the method can potentially be carried out to detect changes in proprioceptive deficits in clinical settings.

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.

The effects of age and amplitude on wrist proprioceptive acuity

This study examined wrist proprioception in a cross-sectional sample of 44 children aged between 8-to 14-years and a control group of 10 neurologically and physically healthy adults. Using a 3-degrees of freedom robotic device, participants performed an ipsilateral joint position matching task in which target amplitude (40% or 80% functional range of motion [fRoM]) and degrees-of-freedom (Flexion/Extension [FE], Radial/Ulnar deviation [RUD], Pronation/Supination [PS]) were manipulated. Results indicated that proprioceptive function became more accurate and consistent over the developmental spectrum, but that the ability to utilize proprioceptive feedback did not reach adult levels till the age of 10-11 years. Furthermore, proprioceptive acuity was influenced by target amplitude, such that movements were more accurate for the 80% fROM compared to the 40% fROM target for both the RUD and PS DoFs, independently of age. The present results provide critical information about the typical development of wrist proprioception that will enable clinicians to chart the course of development and dysfunction in neurological disorders in children, and help establish protocols for the robotic diagnosis and assessment of neurodevelopmental disorders.

Robot-aided developmental assessment of wrist proprioception in children

BACKGROUND

Several 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.

METHODS

Using 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.

RESULTS

First, 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.

CONCLUSIONS

Proprioceptive 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.