Vibro-tactile stimulation of the neck reduces pain in people with cervical dystonia: a proof-of-concept study.

BACKGROUND: Pain is a common non-motor symptom in patients with cervical dystonia (CD), severely impacting their quality of life. The pathophysiology of CD is incompletely understood but it involves altered processing of proprioceptive and pain signals. OBJECTIVES: The purpose of this proof-of-concept study was to determine if vibro-tactile stimulation (VTS)-a non-invasive form of neuromodulation targeting the somatosensory system-can modulate neck pain in people with CD. METHODS: In a multi-center study, 44 CD patients received VTS to sternocleidomastoid and/or trapezius muscles for up to 45 min under 9 different stimulation conditions that either targeted a single or a pair of muscles. The primary outcome measure was a perceived pain score (PPS) rated by participants on a 100-point analogue scale. RESULTS: During VTS, 29/44 (66%) of participants experienced a reduction in PPS of at least 10% with 17/44 (39%) reporting a reduction in pain of 50% or higher. After VTS cessation, 57% of participants still reported a 10% or higher reduction in PPS. Effects were significant at the group level and persisted for up to 20 min post-treatment. No distinct optimal stimulation profiles were identified for specific CD phenotypes. Clinical markers of disease severity or duration did not predict the degree of VTS-induced pain reduction. CONCLUSION: This proof-of-concept study demonstrates the potential of VTS as a new non-invasive therapeutic option for treating neck pain associated with CD. Further research needs to delineate optimal dosage and long-term effects.

Dyad motor learning in a wrist-robotic environment: Learning together is better than learning alone.

OBJECTIVE: Dyad motor practice is characterized by two learners alternating between physical and observational practice, which can lead to better motor outcomes and reduce practice time compared to physical practice alone. Robot-assisted therapy has become an established neurorehabilitation tool but is limited by high therapy cost and access. Implementing dyad practice in robot-assisted rehabilitation has the potential to improve therapeutic outcomes and/or to achieve them faster. This study aims to determine the effects of dyad practice on motor performance in a wrist-robotic environment to evaluate its potential use in robotic rehabilitation settings. METHODS: Forty-two healthy participants (18-35 years) were randomized into three groups (n = 14): Dyad practice, physical practice with rest and physical practice without rest. Participants practiced a 2 degree-of-freedom gamified wrist movement task for 20 trials using a custom-made wrist robotic device. A motor performance score (MPS) that captured temporal and spatial time-series kinematics was computed at baseline, the end of training and 24 h later to assess retention. RESULTS: MPS did not differ between groups at baseline. All groups revealed significant performance gains by the end of training. However, dyads outperformed the other groups at the end of training (p < 0.001) and showed higher retention after 24-h (p = 0.02). Median MPS improved by 46.5% in dyads, 25.3% in physical practice-rest, and 33.6% in physical practice-no rest at the end of training compared to baseline. CONCLUSION: Compared to physical practice alone, dyad practice leads to superior motor outcomes in a robot-assisted motor learning task. Dyads still outperformed their counterparts 24-h after practice. IMPACT STATEMENT: Improving motor function in complex motor tasks without increasing required practice time, dyad practice can optimize therapeutic resources. This is particularly impactful in robot-assisted rehabilitation regimens as it would help to improve patients' outcomes and increase care efficiency.

Ankle proprioception in children with cerebral palsy.

PURPOSE: There is no established clinical standard to evaluate ankle proprioception in children with cerebral palsy (CP). This study compared ankle position sense of children with CP to age-matched children who are typically developing (TD). METHODS: Children aged 6-17 years participated (15 CP, 58 TD). Using a custom-built device, the ankle was passively rotated to two positions for 25 trials. Using a psychophysical forced-choice paradigm, participants indicated which position was more plantarflexed. A psychometric function was fitted to the response data to determine the just noticeable difference (JND) threshold and the associated uncertainty (random error) for ankle position sense. RESULTS: Median JND thresholds for the CP group were elevated (CP: 4.3°, TD: 3.0°). Three children with CP exceeded the 95th percentile of TD. No differences in random error were found. CONCLUSION: This method assessed ankle proprioception relative to norm data and identified position sense impairments in children with CP. Using this method can provide data on proprioceptive status in CP, augmenting the assessment of motor impairment.

A Physically Active Lifestyle Can Protect against Age-Related Decline in Ankle Proprioception.

This study examined whether physically active middle-aged (50-64 years) and older adults (65-80 years) demonstrate age-related ankle proprioceptive decline relative to younger counterparts. Empirical data indicate that ankle proprioception declines with aging and such sensory decline negatively affects balance. Using a passive motion apparatus, we employed a psychophysical forced-choice paradigm in which the ankle was passively plantarflexed to a reference position (15° or 25°) and a comparison position that was always smaller than the reference. Subsequently, participants indicated which position was more plantarflexed. As outcome measures of ankle position sense acuity, a just-noticeable-difference (JND) threshold and the uncertainty area (UA) were derived from the psychometric stimulus-response difference function for each participant. The JND threshold is a measure of proprioceptive bias and UA constitutes a measure of precision. The main results are: First, at the 15° reference, most middle-aged (74%) and older adults (71%) had thresholds within the range of the young adults. The respective median JND threshold of young adults was statistically lower when compared to both older groups. Second, no differences between age groups were observed at the 25° reference. Third, no age-related differences were found for UA at either reference. These data indicate that physically active aging adults may be spared from age-related decline in ankle position sense and that age-related differences emerge for small ankle displacements. The findings underscore the importance of remaining active during aging.

A robot-aided visuomotor wrist training induces motor and proprioceptive learning that transfers to the untrained ipsilateral elbow.

BACKGROUND: Learning of a visuomotor task not only leads to changes in motor performance but also improves proprioceptive function of the trained joint/limb system. Such sensorimotor learning may show intra-joint transfer that is observable at a previously untrained degrees of freedom of the trained joint. OBJECTIVE: Here, we examined if and to what extent such learning transfers to neighboring joints of the same limb and whether such transfer is observable in the motor as well as in the proprioceptive domain. Documenting such intra-limb transfer of sensorimotor learning holds promise for the neurorehabilitation of an impaired joint by training the neighboring joints. METHODS: Using a robotic exoskeleton, 15 healthy young adults (18-35 years) underwent a visuomotor training that required them to make continuous, increasingly precise, small amplitude wrist movements. Wrist and elbow position sense just-noticeable-difference (JND) thresholds and spatial movement accuracy error (MAE) at wrist and elbow in an untrained pointing task were assessed before and immediately after, as well as 24 h after training. RESULTS: First, all participants showed evidence of proprioceptive and motor learning in both trained and untrained joints. The mean JND threshold decreased significantly by 30% in trained wrist (M: 1.26° to 0.88°) and by 35% in untrained elbow (M: 1.96° to 1.28°). Second, mean MAE in untrained pointing task reduced by 20% in trained wrist and the untrained elbow. Third, after 24 h the gains in proprioceptive learning persisted at both joints, while transferred motor learning gains had decayed to such extent that they were no longer significant at the group level. CONCLUSION: Our findings document that a one-time sensorimotor training induces rapid learning gains in proprioceptive acuity and untrained sensorimotor performance at the practiced joint. Importantly, these gains transfer almost fully to the neighboring, proximal joint/limb system.

Atypical Activation of Laryngeal Somatosensory-Motor Cortex During Vocalization in People With Unexplained Chronic Cough.

Importance: Unexplained chronic cough is common and has substantial negative quality-of-life implications, yet its causes are not well understood. A better understanding of how peripheral and central neural processes contribute to chronic cough is essential for treatment design. Objective: To determine if people with chronic cough exhibit signs of abnormal neural processing over laryngeal sensorimotor cortex during voluntary laryngeal motor activity such as vocalization. Design, Setting, and Participants: This was a cross-sectional study of a convenience sample of participants with chronic cough and healthy participants. Testing was performed in an acoustically and electromagnetically shielded chamber. In a single visit, electroencephalographic (EEG) signals were recorded from participants with chronic cough and healthy participants during voice production. The chronic cough group participants presented with unexplained cough of 8 weeks or longer duration with prior medical evaluation including negative results of chest imaging. None of the participants had a history of any neurologic disease known to impair vocalization or swallowing. Data collection for the healthy control group occurred from February 2 to June 28, 2018, and for the chronic cough group, from November 22, 2021, to June 21, 2022. Data analysis was performed from May 1 to October 30, 2022. Exposure: Participants with or without chronic cough. Main Outcome Measures: Event-related spectral perturbation over the laryngeal area of somatosensory-motor cortex from 0 to 30 Hz (ie, θ, α, and ß bands) and event-related coherence as a measure of synchronous activity between somatosensory and motor cortical regions. Results: The chronic cough group comprised 13 participants with chronic cough (mean [SD] age, 63.5 [7.8] years; 9 women and 4 men) and the control group, 10 healthy age-matched individuals (mean [SD] age, 60.3 [13.9] years; 6 women and 4 men). In the chronic cough group, the typical movement-related desynchronization over somatosensory-motor cortex during vocalization was significantly reduced across θ, α, and ß frequency bands when compared with the control group. Conclusions and Relevance: This cross-sectional study found that the typical movement-related suppression of brain oscillatory activity during vocalization is weak or absent in people with chronic cough. Thus, chronic cough affects sensorimotor cortical activity during the asymptomatic voluntary activation of laryngeal muscles.

A Robotic Device for Measuring Human Ankle Motion Sense.

Proprioceptive signals about ankle motion are essential for the control of balance and gait. However, objective, accurate methods for testing ankle motion sense in clinical settings are not established. This study presents a fast and accurate method to assess human ankle motion sense acuity. A one degree-of-freedom (DOF) robotic device was used to passively rotate the ankle under controlled conditions and applied a psychophysical forced-choice paradigm. Twenty healthy participants were recruited for study participation. Within a trial, participants experienced one of three reference velocities (10°/s, 15°/s, and 20°/s), and a smaller comparison velocity. Subsequently, they verbally indicated which of the two movements was faster. As outcome measures, a just-noticeable-difference (JND) threshold and interval of uncertainty (IU) were derived from the psychometric stimulus-response difference function for each participant. Our data show that mean JND threshold increased almost linearly from 0.53°/s at the 10°/s reference to 1.6°/s at 20°/s ( ). Perceptual uncertainty increased similarly (median IU = 0.33°/s at 10°/s and 0.97°/s at 20°/s; ). Both measures were strongly correlated ( r s = 0.70). This implies that the bias of the human ankle motion sense is approximately 5 - 8% of the experienced movement velocity. We demonstrate that this robot-aided test produces quantitative data on human ankle motion sense acuity. It provides a useful addition to the current measures of ankle proprioceptive function.

Identifying body awareness-related brain network changes after Spring Forest Qigong™ practice or P.Volve low-intensity exercise in adults with chronic low back pain: a feasibility Phase I Randomized Clinical Trial.

Background: Chronic low back pain (cLBP) affects the quality of life of 52 million Americans and leads to an enormous personal and economic burden. A multidisciplinary approach to cLBP management is recommended. Since medication has limited efficacy and there are mounting concerns about opioid addiction, the American College of Physicians and American Pain Society recommend non-pharmacological interventions, such as mind and body approaches (e.g., Qigong, yoga, Tai Chi) before prescribing medications. Of those, Qigong practice might be most accessible given its gentle movements and because it can be performed standing, sitting, or lying down. The three available Qigong studies in adults with cLBP showed that Qigong reduced pain more than waitlist and equally well than exercise. Yet, the duration and/or frequency of Qigong practice were low (<12 weeks or less than 3x/week). The objectives of this study were to investigate the feasibility of practicing Spring Forest Qigong™ or performing P.Volve low intensity exercises 3x/week for 12 weeks, feasibility of recruitment, data collection, delivery of the intervention as intended, as well as identify estimates of efficacy on brain function and behavioral outcomes after Qigong practice or exercise. To our knowledge, this is the first study investigating the feasibility of the potential effect of Qigong on brain function in adults with cLBP. Methods: We conducted a feasibility Phase I Randomized Clinical Trial. Of the 36 adults with cLBP recruited between January 2020 and June 2021, 32 were enrolled and randomized to either 12 weeks of remote Spring Forest Qigong™ practice or remote P.Volve low-intensity exercises. Participants practiced at least 3x/week for 41min/session with online videos. Our main outcome measures were the Numeric Pain Rating Scale (highest, average, and lowest cLBP pain intensity levels in the prior week), assessed weekly and fMRI data (resting-state and task-based fMRI tasks: pain imagery, kinesthetic imagery of a Qigong movement, and robot-guided shape discrimination). We compared baseline resting-state connectivity and brain activation during fMRI tasks in adults with cLBP with data from a healthy control group (n=28) acquired in a prior study. Secondary outcomes included measures of function, disability, body awareness, kinesiophobia, balance, self-efficacy, core muscle strength, and ankle proprioceptive acuity with a custom-build device. Results: Feasibility of the study design and methods was demonstrated with 30 participants completing the study (94% retention) and reporting high satisfaction with the programs; 96% adherence to P.Volve low-intensity exercises, and 128% of the required practice intensity for Spring Forest Qigong™ practice. Both groups saw promising reductions in low back pain (effect sizes Cohen's d =1.01-2.22) and in most other outcomes ( d =0.90-2.33). Markers of ankle proprioception were not significantly elevated in the cLBP group after the interventions. Brain imaging analysis showed weaker parietal operculum and insula network connectivity in adults with cLBP (n=26), compared to data from a healthy control group (n=28). The pain imagery task elicited lower brain activation of insula, parietal operculum, angular gyrus and supramarginal gyrus at baseline in adults with cLBP than in healthy adults. Adults with cLBP had lower precentral gyrus activation than healthy adults for the Qigong movement and robot task at baseline. Pre-post brain function changes showed individual variability: Six (out of 13) participants in the Qigong group showed increased activation in the parietal operculum, angular gyrus, supramarginal gyrus, and precentral gyrus during the Qigong fMRI task. Interpretation: Our data indicate the feasibility and acceptability of using Spring Forest Qigong™ practice or P.Volve low-intensity exercises for cLBP relief showing promising results in terms of pain relief and associated symptoms. Our brain imaging results indicated brain function improvements after 12 weeks of Qigong practice in some participants, pointing to the need for further investigation in larger studies. Trial registration number: ClinicalTrials.gov: NCT04164225 .

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.

The Effectiveness of Proprioceptive Training for Improving Motor Performance and Motor Dysfunction: A Systematic Review.

Objective: Proprioceptive training is any intervention aiming to improve proprioceptive function with the ultimate goal to enhance motor function and performance. It has been promoted as an approach to enhance athletic performance and as a tool for sensorimotor rehabilitation. Numerous studies sought to provide evidence on the effectiveness of the approach. However, many different training regimes claiming to train proprioception report a variety of sensorimotor measures that are not directly comparable. This, in turn, makes it difficult to assess effectiveness across approaches. It is the objective of this study to systematically review recent empirical evidence to gain an understanding of which outcome measures are most sensitive, which populations may benefit most from proprioceptive training, and what are the effects on proprioceptive and motor systems. Methods: Four major databases were searched. The following inclusion criteria were applied: (1) A quantified pre- and post-treatment measure of proprioceptive function. (2) An intervention or training program believed to influence or enhance proprioceptive function. (3) Contained at least one form of treatment or outcome measure that is indicative of somatosensory function and not confounded by information from other sensory modalities. 4) The study reported of at least one quantified measure of motor performance. Results: Of the 3,297 articles identified by the database search, 70 studies met the inclusion criteria and were included for further review. Across studies, proprioceptive training led to comparable gains in both proprioceptive (+46%) and motor performance (+45%). The majority of studies (50/70) applied active movement interventions. Interventions applying somatosensory stimulation were most successful in clinical populations. Joint position sense error (JPSE) was the most commonly used proprioceptive measure and presents a reliable and feasible measure for clinical use. Conclusion: Proprioceptive training can lead to significant improvements in proprioceptive and motor function across a range healthy and clinical populations. Regimens requiring active movement of the trainee tended to be most successful in improving sensorimotor performance. Conclusive evidence on how long training gains are retained is still lacking. There is no solid evidence about the underlying long-term neuroplastic changes associated proprioceptive training.

The CCAS-scale in hereditary ataxias: helpful on the group level, particularly in SCA3, but limited in individual patients.

BACKGROUND: A brief bedside test has recently been introduced by Hoche et al. (Brain, 2018) to screen for the Cerebellar Cognitive Affective Syndrome (CCAS) in patients with cerebellar disease. OBJECTIVE: This multicenter study tested the ability of the CCAS-Scale to diagnose CCAS in individual patients with common forms of hereditary ataxia. METHODS: A German version of the CCAS-Scale was applied in 30 SCA3, 14 SCA6 and 20 FRDA patients, and 64 healthy participants matched for age, sex, and level of education. Based on original cut-off values, the number of failed test items was assessed, and CCAS was considered possible (one failed item), probable (two failed items) or definite (three failed items). In addition a total sum raw score was calculated. RESULTS: On a group level, failed items were significantly higher and total sum scores were significantly lower in SCA3 patients compared to matched controls. SCA6 and FRDA patients performed numerically below controls, but respective group differences failed to reach significance. The ability of the CCAS-Scale to diagnose CCAS in individual patients was limited to severe cases failing three or more items. Milder cases failing one or two items showed a great overlap with the performance of controls exhibiting a substantial number of false-positive test results. The word fluency test items differentiated best between patients and controls. CONCLUSIONS: As a group, SCA3 patients performed below the level of SCA6 and FRDA patients, possibly reflecting additional cerebral involvement. Moreover, the application of the CCAS-Scale in its present form results in a high number of false-positive test results, that is identifying controls as patients, reducing its usefulness as a screening tool for CCAS in individual patients.

Motor training-related brain reorganization in patients with cerebellar degeneration.

Cerebellar degeneration progressively impairs motor function. Recent research showed that cerebellar patients can improve motor performance with practice, but the optimal feedback type (visual, proprioceptive, verbal) for such learning and the underlying neuroplastic changes are unknown. Here, patients with cerebellar degeneration (N = 40) and age- and sex-matched healthy controls (N = 40) practiced single-joint, goal-directed forearm movements for 5 days. Cerebellar patients improved performance during visuomotor practice, but a training focusing on either proprioceptive feedback, or explicit verbal feedback and instruction did not show additional benefits. Voxel-based morphometry revealed that after training gray matter volume (GMV) was increased prominently in the visual association cortices of controls, whereas cerebellar patients exhibited GMV increase predominantly in premotor cortex. The premotor cortex as a recipient of cerebellar efferents appears to be an important hub in compensatory remodeling following damage of the cerebro-cerebellar motor system.

Vibro-Tactile Stimulation as a Non-Invasive Neuromodulation Therapy for Cervical Dystonia: A Case Study.

INTRODUCTION: Cervical dystonia (CD) is a type of focal dystonia that is characterized by involuntary neck postures. The underlying neurophysiology mechanism of CD is unknown, but there is increasing empirical evidence that motor deficits of CD are associated with somatosensory and proprioceptive deficits in the upper limb area. Vibro-tactile stimulation (VTS) is a non-invasive somatosensory stimulation approach where afferent signals from the vibrated muscle and tactile mechanoreceptors modulate cortical activity. Previous studies have shown that VTS could be an effective neuromodulation therapy for treating laryngeal dystonia. This proof-of-concept study examined the effect of VTS on alleviating the involuntary cervical muscle contractions in a female participant with intermittent torticollis. METHODS: VTS was applied sequentially on four neck positions: bilateral trapezius (TRP) and bilateral sternocleidomastoid (SCM). Each VTS site was vibrated continuously for six minutes. The kinematics and underlying neck muscle activities during dystonic neck movements were examined with acceleration and surface electromyography (sEMG). To quantify the efficacy of VTS, two acceleration features and one sEMG feature were derived: (1) number of acceleration peaks per minute; (2) peak amplitude of acceleration (PAA); (3) change in power of sEMG after VTS. RESULTS: The frequency of intermittent dystonic neck movements decreased by 60% after VTS. In addition, PAA during dystonic episodes was drastically reduced after VTS when compared to baseline. Third, the effectiveness of VTS in alleviating dystonic muscle spasms depended on the site of vibration. For this participant, the left trapezius muscle was shown as the optimal vibration site reducing sEMG signal power by 15% across all recorded muscles. CONCLUSION: This case study offered preliminary insight into the assumed effectiveness of neck muscle VTS as a treatment for CD. Our participant experienced pain relief after VTS with measured improvements reflected by electrophysiological and kinematic data. A systematic study with a larger sample size is required in the future to validate the effectiveness of VTS for treating symptoms in CD.

Effects of a robot-aided somatosensory training on proprioception and motor function in stroke survivors.

BACKGROUND: Proprioceptive deficits after stroke are associated with poor upper limb function, slower motor recovery, and decreased self-care ability. Improving proprioception should enhance motor control in stroke survivors, but current evidence is inconclusive. Thus, this study examined whether a robot-aided somatosensory-based training requiring increasingly accurate active wrist movements improves proprioceptive acuity as well as motor performance in chronic stroke. METHODS: Twelve adults with chronic stroke completed a 2-day training (age range: 42-74 years; median time-after-stroke: 12 months; median Fugl-Meyer UE: 65). Retention was assessed at Day 5. Grasping the handle of a wrist-robotic exoskeleton, participants trained to roll a virtual ball to a target through continuous wrist adduction/abduction movements. During training vision was occluded, but participants received real-time, vibro-tactile feedback on their forearm about ball position and speed. Primary outcome was the just-noticeable-difference (JND) wrist position sense threshold as a measure of proprioceptive acuity. Secondary outcomes were spatial error in an untrained wrist tracing task and somatosensory-evoked potentials (SEP) as a neural correlate of proprioceptive function. Ten neurologically-intact adults were recruited to serve as non-stroke controls for matched age, gender and hand dominance (age range: 44 to 79 years; 6 women, 4 men). RESULTS: Participants significantly reduced JND thresholds at posttest and retention (Stroke group: pretest: mean: 1.77° [SD: 0.54°] to posttest mean: 1.38° [0.34°]; Control group: 1.50° [0.46°] to posttest mean: 1.45° [SD: 0.54°]; F[2,37] = 4.54, p = 0.017, ηp2 = 0.20) in both groups. A higher pretest JND threshold was associated with a higher threshold reduction at posttest and retention (r = - 0.86, - 0.90, p ≤ 0.001) among the stroke participants. Error in the untrained tracing task was reduced by 22 % at posttest, yielding an effect size of w = 0.13. Stroke participants exhibited significantly reduced P27-N30 peak-to-peak SEP amplitude at pretest (U = 11, p = 0.03) compared to the non-stroke group. SEP measures did not change systematically with training. CONCLUSIONS: This study provides proof-of-concept that non-visual, proprioceptive training can induce fast, measurable improvements in proprioceptive function in chronic stroke survivors. There is encouraging but inconclusive evidence that such somatosensory learning transfers to untrained motor tasks. Trial registration Clinicaltrials.gov; Registration ID: NCT02565407; Date of registration: 01/10/2015; URL: https://clinicaltrials.gov/ct2/show/NCT02565407 .

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.

Neurostructural changes and declining sensorimotor function due to cerebellar cortical degeneration.

Neurodegeneration of the cerebellum progresses over years and primarily affects cerebellar cortex. It leads to a progressive loss of control and coordination of gait, posture, speech, fine motor, and oculomotor function. Yet, little is known how the cerebro-cerebellar network compensates for the loss in cerebellar cortical neurons. To address this knowledge gap, we examined 30 people with cerebellar cortical degeneration and a group of 30 healthy controls. We assessed visuomotor performance during a forearm-pointing task to 10°, 25°, and 50° targets. In addition, using MRI imaging, we determined neurodegenerative-induced changes in gray matter volume (GMV) in the cerebro-cerebellar network and correlated them to markers of motor performance. The main results are as follows: first, the relative joint position error (RJPE) during pointing was significantly greater in the ataxia group for all targets confirming the expected motor control deficit. Second, in the ataxia group, GMV was significantly reduced in cerebellar cortex but increased in the deep cerebellar nuclei. Motor error (RJPE) correlated negatively with decreased cerebellar GMV but positively with increased GMV in supplementary motor area (SMA) and premotor cortex. GMV of the deep cerebellar nuclei did not correlate significantly with markers of motor performance. We discuss whether the GMV changes in the cerebellar output nuclei and the extracerebellar efferent targets in secondary motor cortex can be understood as a central compensatory response to the neurodegeneration of the cerebellar cortex.NEW & NOTEWORTHY Neurodegeneration of the cerebellum progresses over years and primarily affects cerebellar cortex. It leads to a progressive loss of control and coordination of movement. We here show that the neurodegenerative process not only leads to cells loss in cerebellar cortex but also induces neurostructural changes in the form of increased gray matter in the efferent targets of the cerebellar cortex, namely, the cerebellar output nuclei, the SMA, and premotor cortex.

A robot-aided visuomotor wrist training induces gains in proprioceptive and movement accuracy in the contralateral wrist.

Proprioceptive training is a neurorehabilitation approach known to improve proprioceptive acuity and motor performance of a joint/limb system. Here, we examined if such learning transfers to the contralateral joints. Using a robotic exoskeleton, 15 healthy, right-handed adults (18-35 years) trained a visuomotor task that required making increasingly small wrist movements challenging proprioceptive function. Wrist position sense just-noticeable-difference thresholds (JND) and spatial movement accuracy error (MAE) in a wrist-pointing task that was not trained were assessed before and immediately as well as 24 h after training. The main results are: first, training reduced JND thresholds (- 27%) and MAE (- 33%) in the trained right wrist. Sensory and motor gains were observable 24 h after training. Second, in the untrained left wrist, mean JND significantly decreased (- 32%) at posttest. However, at retention the effect was no longer significant. Third, motor error at the untrained wrist declined slowly. Gains were not significant at posttest, but MAE was significantly reduced (- 27%) at retention. This study provides first evidence that proprioceptive-focused visuomotor training can induce proprioceptive and motor gains not only in the trained joint but also in the contralateral, homologous joint. We discuss the possible neurophysiological mechanism behind such sensorimotor transfer and its implications for neurorehabilitation.

Upper limb proprioception and fine motor function in young pianists.

BACKGROUND: This study investigated if intensive piano training may be associated with improved motor and somatosensory function. We systematically examined upper limb proprioception, which is known to play an essential role in skill movements, and motor function in young pianists. METHOD: Forty-four typically developing children who either regularly played piano for more than six years (N = 16) or had no experience playing musical instruments (N = 28) participated. Elbow and wrist joint proprioceptive acuity was assessed using a manipulandum. The wrist/elbow was passively flexed to a target with participants actively trying to match the just experienced target position. Motor function was assessed using the Movement Assessment Battery for Children (MABC-2). RESULTS: First, children in the pianist group exhibited significantly lower position sense bias (systematic error) at both the elbow and wrist when compared to controls. Position sense precision (random error) was not different between groups. Second, the piano group exhibited enhanced fine motor function as shown by higher manual dexterity MABC-2 scores. Performance in other motor domains (aiming and catching or balance) was not improved in young pianists. Third, a lower position sense bias was correlated with a higher level of manual dexterity. CONCLUSION: This study documents that children who regularly play the piano have superior upper limb position sense acuity. Specifically, smaller position sense bias, i.e., less systematic error. Superior upper position sense acuity in young pianists is associated with higher fine motor functions.