Does the nervous system depend on kinesthetic information to control natural limb movements?

The Effect of Muscle Fatigue on the Knee Proprioception: A Systematic Review

This study aimed to systematically review and summarise the evidence about the effect of muscle fatigue on the knee proprioception of trained and non-trained individuals. A search in PubMed, Scopus, Web of Science and EBSCO databases and Google Scholar was conducted using the expression: "fatigue" AND ("proprioception" OR "position sense" OR "repositioning" OR "kinesthesia" OR "detection of passive motion" OR "force sense" OR "sense of resistance") AND "knee". Forty-two studies were included. Regarding joint-position sense, higher repositioning errors were reported after local and general protocols. Kinesthesia seems to be more affected when fatigue is induced locally, and force sense when assessed at higher target forces and after eccentric protocols. Muscle fatigue, both induced locally or generally, has a negative impact on the knee proprioception.

Fatiguing unilateral handgrip influences force during force-matching task with lower limb

This study aimed to test the hypotheses that fatiguing unilateral handgrip contraction exhibits different changes in corticomotor excitability, which is evaluated by motor-evoked potentials (MEPs), in the lower limbs ipsilateral and contralateral to the fatigued hand, and that the changes in corticomotor excitability estimated by MEPs in the non-fatigued lower limbs affect the force exerted based on the sense of effort. Ten healthy males completed fatiguing unilateral handgrip contraction and force-matching tasks by static dorsiflexion before, immediately after, and 10 min after handgrip contraction. MEPs in the tibialis anterior (TA) were also measured before, immediately after, and 10 min after handgrip contraction. Fatiguing handgrip contractions resulted in asymmetrical MEPs in the TA muscles. Specifically, MEPs in the contralateral TA muscle were significantly increased (158 ± 60 %) and MEPs in the contralateral TA muscle were greater after the handgrip contraction than the ipsilateral MEPs (111 ± 30 %). Moreover, the torque exerted during the force-matching task significantly increased only in the contralateral ankle after the fatiguing handgrip contraction. Fatiguing unilateral handgrip contraction results in asymmetric changes in corticomotor excitability in the TA muscle, and the force exerted during the force-matching task based on the sense of effort becomes higher in the TA muscle with greater corticomotor excitability than that before fatiguing unilateral handgrip contraction.

Dissociation between dreams and wakefulness: Insights from body and action representations of rare individuals with massive somatosensory deafferentation

The realism of body and actions in dreams is thought to be induced by simulations based on internal representations used during wakefulness. As somatosensory signals contribute to the updating of body and action representations, these are impaired when somatosensory signals are lacking. Here, we tested the hypothesis that individuals with somatosensory deafferentation have impaired body and actions in their dreams, as in wakefulness. We questioned three individuals with a severe, acquired sensory neuropathy on their dreams. While deafferented participants were impaired in daily life, they could dream of themselves as able-bodied, with some sensations (touch, proprioception) and actions (such as running or jumping) which had not been experienced in physical life since deafferentation. We speculate that simulation in dreams could be based on former, "healthy" body and action representations. Our findings are consistent with the idea that distinct body and action representations may be used during dreams and wakefulness.

Clinical characteristics and diagnostic aspects of cervicogenic dizziness in patients with chronic dizziness: A cross-sectional study

BACKGROUND AND OBJECTIVES

Chronic dizziness can significantly affect quality of life, but identifying the underlying cause remains challenging. This study focuses on proprioceptive cervicogenic dizziness (CGD) and aims: (1) to compare clinical test results between patients with CGD, dizzy patients without CGD, and healthy controls; and (2) to evaluate the diagnostic value of the clinical tests for CGD in patients with chronic dizziness.

METHODS

Sixty patients with chronic dizziness (18 with CGD and 42 without CGD), and 43 healthy controls underwent clinical tests evaluating neck function (mobility, proprioception, muscle function and disability), balance control, and the presence of visually induced dizziness. Data were analysed through one-way ANOVA, chi-square, independent samples t-test, and logistic regression analyses.

RESULTS

Patients with CGD had significantly more neck pain-related disability (Neck Bournemouth questionnaire (NBQ), p = 0.006), but better static (Static Balance, p = 0.001) and dynamic balance (Tandem Gait, p = 0.049), compared to dizzy patients without CGD. Univariable analyses revealed that increased NBQ (OR 1.05 [1.01; 1.09], p = 0.017), Joint Position Error (JPE) _{after extension} (OR 1.52 [1.00; 2.32], p = 0.050), and Tandem Gait scores (OR 1.09 [1.01; 1.18], p = 0.046) were individually associated with higher odds of having CGD. Their optimal cut-off level (based on the maximum Youden index) had high sensitivity but low specificity for CGD. The multivariable model, including NBQ and Tandem Gait, had fair discriminative ability (AUC = 0.74, 95% CI [0.61; 0.87]).

CONCLUSION

The combined use of the NBQ and Tandem Gait tests had the highest discriminative ability to detect CGD in patients with chronic dizziness.

Effect of vibrotactile stimulation of the hallux nail on segmental coordination: A secondary analysis using uncontrolled manifold analysis

Controlling center of mass (CoM) movement in the mediolateral direction is imperative for stable walking. During walking, CoM movement is adjusted by the coordination of each body segment, which can be evaluated using uncontrolled manifold (UCM) analysis. UCM analysis evaluates segmental coordination by analyzing variablity in motor movement among the different segments of the body. The vibrotactile stimulation of the hallux nail can augment the sensory information of the plantar surface for necessary motor control. This study aims to investigate the effect of the vibrotactile stimulation of the hallux nail on segmental coordination to control CoM movement in the mediolateral direction during walking. Thirteen healthy men participated in the study. A vibrator was attached to each hallux nail, and pressure sensors were placed under the hallux balls. When the hallux ball was in contact with the floor, vibration stimulation was applied. A three-dimensional motion analysis system was used to measure the segment angles during walking, and UCM analysis was used to evaluate kinematic synergy for controlling CoM movement in the mediolateral direction. Subsequently, segment angles were used as an elemental variable. The synergy index and bad variability as motor noise were negatively related to the status without the stimulation. Vibrotactile stimulation in young people was more effective for people with large motor noise and a small synergy index during the single-stance phase. Thus, kinematic synergy can be immediately changed by sensory input using vibrotactile stimulation of the hallux nail, although applying vibration stimulation should be considered in advance.

Joint Specificity and Lateralization of Upper Limb Proprioceptive Perception

Proprioception is the sense of position and movement of body segments. The widespread distribution of proprioceptors in human anatomy raises questions about proprioceptive uniformity across different body parts. For the upper limbs, previous research, using mostly active and/or contralateral matching tasks, has suggested better proprioception of the non-preferred arm, and at the elbow rather than the wrist. Here we assessed proprioceptive perception through an ipsilateral passive matching task by comparing the elbow and wrist joints of the preferred and non-preferred arms. We hypothesized that upper limb proprioception would be better at the elbow of the non-preferred arm. We found signed errors to be less variable at the non-preferred elbow than at the preferred elbow and both wrists. Signed errors at the elbow were also more stable than at the wrist. Across individuals, signed errors at the preferred and non-preferred elbows were correlated. Also, variable signed errors at the preferred wrist, non-preferred wrist, and preferred elbow were correlated. These correlations suggest that an individual with relatively consistent matching errors at one joint may have relatively consistent matching errors at another joint. Our findings also support the view that proprioceptive perception varies across upper limb joints, meaning that a single joint assessment is insufficient to provide a general assessment of an individual's proprioception.

Enabling visually impaired people to learn three-dimensional tactile graphics with a 3DOF haptic mouse

Background

In this work, we present a novel sensory substitution system that enables to learn three dimensional digital information via touch when vision is unavailable. The system is based on a mouse-shaped device, designed to jointly perceive, with one finger only, local tactile height and inclination cues of arbitrary scalar fields. The device hosts a tactile actuator with three degrees of freedom: elevation, roll and pitch. The actuator approximates the tactile interaction with a plane tangential to the contact point between the finger and the field. Spatial information can therefore be mentally constructed by integrating local and global tactile cues: the actuator provides local cues, whereas proprioception associated with the mouse motion provides the global cues.

Methods

The efficacy of the system is measured by a virtual/real object-matching task. Twenty-four gender and age-matched participants (one blind and one blindfolded sighted group) matched a tactile dictionary of virtual objects with their 3D-printed solid version. The exploration of the virtual objects happened in three conditions, i.e., with isolated or combined height and inclination cues. We investigated the performance and the mental cost of approximating virtual objects in these tactile conditions.

Results

In both groups, elevation and inclination cues were sufficient to recognize the tactile dictionary, but their combination worked at best. The presence of elevation decreased a subjective estimate of mental effort. Interestingly, only visually impaired participants were aware of their performance and were able to predict it.

Conclusions

The proposed technology could facilitate the learning of science, engineering and mathematics in absence of vision, being also an industrial low-cost solution to make graphical user interfaces accessible for people with vision loss.

Effect of robotic-assisted ankle training on gait in stroke participants: A case series study

BACKGROUND

Robotic rehabilitation therapy has grown rapidly during the last two decades allowing researchers and clinicians to deliver high-intensity training to persons with sensorimotor disorders caused by neurological injuries and diseases.

METHODS

This case series reports the effect of robot-assisted, impairment-oriented training for persons recovering from stroke on impairment of the paretic ankle as well as on the kinematic and spatiotemporal parameters of gait. Five persons with chronic stroke (>6 months post-stroke) participated in a 10-week training protocol, receiving three, 30-min sessions per week of a robot-assisted therapy. The robot-assisted intervention cyclically induced dorsiflexion and plantarflexion to the ankle at 5 degrees/s through ±15 degrees while the participants assisted with the imposed movement. Concurrently, participants received visual feedback of their active, assistive torque as well as targeted mechanical vibration of the ankle tendons when lengthened by the applied motion. Walking speed, cadence, step length of the non-paretic leg, percentage of paretic single limb support during the gait cycle, and ankle strength were assessed just before training began (baseline), after the last training session (post-training), and 3 months post-training (follow-up).

DISCUSSION

Robot-assisted training that provided assisted movement, biofeedback, and proprioceptive stimulation reduced ankle impairment and improved kinematic and spatiotemporal gait parameters, suggesting that impairment-oriented therapy applied to the paretic ankle may provide a valuable adjunct to locomotor therapies in persons with chronic gait disorders due to stroke.

Effects of neuromuscular training on knee proprioception in individuals with anterior cruciate ligament injury: a systematic review and GRADE evidence synthesis

OBJECTIVE

To systematically review and summarise the evidence for the effects of neuromuscular training compared with any other therapy (conventional training/sham) on knee proprioception following anterior cruciate ligament (ACL) injury.

DESIGN

Systematic Review.

DATA SOURCES

PubMed, CINAHL, SPORTDiscus, AMED, Scopus and Physical Education Index were searched from inception to February 2020.

ELIGIBILITY CRITERIA

Randomised controlled trials (RCTs) and controlled clinical trials investigating the effects of neuromuscular training on knee-specific proprioception tests following a unilateral ACL injury were included.

DATA EXTRACTION AND SYNTHESIS

Two reviewers independently screened and extracted data and assessed risk of bias of the eligible studies using the Cochrane risk of bias 2 tool. Overall certainty in evidence was determined using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) tool.

RESULTS

Of 2706 articles retrieved, only 9 RCTs, comprising 327 individuals with an ACL reconstruction (ACLR), met the inclusion criteria. Neuromuscular training interventions varied across studies: whole body vibration therapy, Nintendo-Wii-Fit training, balance training, sport-specific exercises, backward walking, etc. Outcome measures included joint position sense (JPS; n=7), thresholds to detect passive motion (TTDPM; n=3) or quadriceps force control (QFC; n=1). Overall, between-group mean differences indicated inconsistent findings with an increase or decrease of errors associated with JPS by ≤2°, TTDPM by ≤1.5° and QFC by ≤6 Nm in the ACLR knee following neuromuscular training. Owing to serious concerns with three or more GRADE domains (risk of bias, inconsistency, indirectness or imprecision associated with the findings) for each outcome of interest across studies, the certainty of evidence was very low.

CONCLUSIONS

The heterogeneity of interventions, methodological limitations, inconsistency of effects (on JPS/TTDPM/QFC) preclude recommendation of one optimal neuromuscular training intervention for improving proprioception following ACL injury in clinical practice. There is a need for methodologically robust RCTs with homogenous populations with ACL injury (managed conservatively or with reconstruction), novel/well-designed neuromuscular training and valid proprioception assessments, which also seem to be lacking.

PROSPERO REGISTRATION NUMBER

CRD42018107349.

INFLUENCE OF FOAM ROLLING ON ELBOW PROPRIOCEPTION, STRENGTH, AND FUNCTIONAL MOTOR PERFORMANCE

CONTEXT

Foam rolling has recently been used frequently to increase flexibility. However, its effects on proprioception, strength and motor performance are not well known. In addition, very few studies have examined the effects of foam rolling in the upper extremity.

OBJECTIVE

To investigate the effects of foam rolling on elbow proprioception, strength, and functional motor performance in healthy individuals.

DESIGN

Randomized controlled study.

SETTING

Exercise laboratory of X Department, X University.

PATIENTS OR OTHER PARTICIPANTS

Sixty healthy participants (mean age=22.83±4.07 years).

INTERVENTION(S)

We randomly assigned participants into two groups: the foam rolling group (FRG) (4 weeks of foam rolling for the biceps brachii muscle) and control group (CG) (no foam rolling).

MAIN OUTCOME MEASURE(S)

We evaluated proprioception (joint position sense [JPS] and force matching), biceps brachii muscle strength, and functional motor performance (modified pull-up test [MPUT], closed kinetic chain upper extremity stability test [CKCUEST], and push-up test) at the baseline, and at the end of the 4th week and 8th week.

RESULTS

JPS at 45° elbow flexion, muscle strength, CKCUEST, and push-up test results improved after foam rolling and improvement was maintained at the follow-up (p<0.017). While the changes in groups for the results of proprioception and CKCUEST were similar among the three time points (p>0.05), there were significant improvements for the muscle strength from baseline to the second evaluation, and from baseline to the follow-up (p<0.001) in the FRG compared to the CG (p=0.004). The FRG was superior to the CG in the improvement of push-up test results among the three time points (p=0.040, p=0.001, p<0.001). Other data did not change (p>0.05).

CONCLUSION

Foam rolling is effective in improving elbow JPS in small flexion angles, biceps brachii strength, and some parameters of upper extremity functional motor performance. These effects are maintained 4 weeks after application.

Muscle pain from an intramuscular injection of hypertonic saline increases variability in knee extensor torque reproduction

The intensity of exercise-induced pain (EIP) reflects the metabolic environment in the exercising muscle, so during endurance exercise, this may inform the intelligent regulation of work rate. Conversely, the acute debilitating effects of EIP on motor unit recruitment could impair the estimation of force produced by the muscle and impair judgement of current exercise intensity. This study investigated whether muscle pain that feels like EIP, administered via intramuscular injection of hypertonic saline, interferes with the ability to accurately reproduce torque in a muscle group relevant to locomotive exercise. On separate days, 14 participants completed an isometric torque reproduction task of the knee extensors. Participants were required to produce torque at 15% and 20% maximal voluntary isometric torque (MVIT), without visual feedback before (baseline), during (pain/no pain), and after (recovery) an injection of 0.9% isotonic saline (Control) or 5.8% hypertonic saline (Experimental) into the vastus lateralis of the right leg. An elevated reported intensity of pain, and a significantly increased variance in mean contraction torque at both 15% (P = 0.049) and 20% (P = 0.002) MVIT was observed in the Experimental compared to the Control condition. Both 15 and 20% target torques were performed at a similar pain intensity in the Experimental condition (15% MVIT: 4.2 ± 1.9; 20% MVIT: 4.5 ± 2.2; P > 0.05). These findings demonstrate that the increased muscle pain from the injection of hypertonic saline impeded accurate reproduction of knee extensor torque. These findings have implications for the detrimental impact of EIP on exercise regulation and endurance performance.NEW & NOTEWORTHY We provide novel data demonstrating that the presence of muscle pain interferes with estimations of torque produced by the knee extensors, which could impair judgment of work rate during endurance exercise. The novelty of our study is in the application of the hypertonic saline experimental model into a quadriceps muscle during short, submaximal isometric contractions at an intensity that provides a more translatable assessment of the impact of exercise-induced pain on work-rate regulation during whole body exercise.

Somatosensory temporal discrimination threshold changes during motor learning

PURPOSE

Mechanisms underlying the somatosensory temporal discrimination threshold and its relationship with motor control have been reported; however, little is known regarding the change in temporal processing of tactile information during motor learning. We investigated the somatosensory temporal discrimination threshold changes during motor learning in a feedback-control task.

MATERIALS AND METHODS

We included 15 healthy individuals. The somatosensory temporal discrimination threshold was measured on the index finger. A 10-session coin rotation task was performed, with 2 min' training per session. The coin rotation scores were determined through tests (continuous coin rotation at 180° at maximum speed for 10 s). The coin rotation test score and the somatosensory temporal discrimination threshold were determined at baseline and after 5 and 10 sets of training, as follows: pre-test; training_5set (1 set × 5); post-test_5block; training_5set (1 set × 5); and post-test_10block. The coin rotation score and the somatosensory temporal discrimination threshold were compared between the tests. The latter was also compared between the right (the within-subject control) and left fingers.

RESULTS

The coin rotation score showed significant differences among all tests. In the somatosensory temporal discrimination threshold, there was a significant difference between the pre-test and post-test_5block values, pre-test and post-test_10block values of the left side and between the right and left sides in the post-test_5block and the post-test_10block values.

CONCLUSIONS

The somatosensory temporal discrimination threshold decreased along with task-performance progress following motor learning during a feedback-control task.

The Necessity of Ambiguity in Self-Other Processing: A Psychosocial Perspective With Implications for Mental Health

While distinguishing between the actions and physical boundaries of self and other (non-self) is usually straightforward there are contexts in which such differentiation is challenging. For example, self-other ambiguity may occur when actions of others are similar or complementary to those of the self. Even in the absence of such situational challenges, individuals experiencing hallucinations have difficulties with this distinction, often experiencing thoughts or actions of self as belonging to other agents. This paper explores the role of ambiguity in self-other differentiation, drawing from developmental, psychodynamic, and neurocognitive perspectives. A key proposal is that engagement in contexts that make distinctions between self and other challenging yet necessary allow reality-testing skills related to agency to develop. Attunement in typical caregiver-infant interactions is framed as a safe but inherently ambiguous environment that provides optimal condition for the infant to develop a coherent self-other sense. Vulnerability to psychosis may be related to limited access to such an environment in early development. However, the perceptual, cognitive, and social skills that contribution to attribution are likely to be malleable following infancy and improve though opportunities for boundary play in similarly ambiguous settings. Using music-making to illustrate, we postulate that engagement in intricate joint-actions that blurs agentic boundaries can contribute to the continued development of an adaptive sense of self and other essential to healthy social functioning. Increased insight into the self-other ambiguity may enhance our understanding of mechanisms underlying "self-disorders" such as schizophrenia and eventually extend the range of social and arts-based therapeutic possibilities.

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.

CUSUM analysis of learning curves for the head-mounted microscope in phonomicrosurgery

OBJECTIVES/HYPOTHESIS

To observe the learning curve of the head-mounted microscope in a phonomicrosurgery simulator using cumulative summation (CUSUM) analysis, which incorporates a magnetic phonomicrosurgery instrument tracking system (MPTS).

STUDY DESIGN

Retrospective case series.

METHODS

Eight subjects (6 medical students and 2 surgeons inexperienced in phonomicrosurgery) operated on phonomicrosurgical simulation cutting tasks while using the head-mounted microscope for 400 minutes total. Two 20-minute sessions occurred each day for 10 total days, with operation quality (Qs ) and completion time (T) being recorded after each session. Cumulative summation analysis of Qs and T was performed by using subjects' performance data from trials completed using a traditional standing microscope as success criteria.

RESULTS

The motion parameters from the head-mounted microscope were significantly better than the standing microscope (P < 0.01), but T was longer than that from the standing microscope (P < 0.01). No subject successfully adapted to the head-mounted microscope, as assessed by CUSUM analysis.

CONCLUSION

Cumulative summation analysis can objectively monitor the learning process associated with a phonomicrosurgical simulator system, ultimately providing a tool to assess learning status. Also, motion parameters determined by our MPTS showed that, although the head-mounted microscope provides better motion control, worse Qs and longer T resulted. This decrease in Qs is likely a result of the relatively unstable visual environment that it provides. Overall, the inexperienced surgeons participating in this study failed to adapt to the head-mounted microscope in our simulated phonomicrosurgery environment.

LEVEL OF EVIDENCE

4 Laryngoscope, 126:2295-2300, 2016.

The Right Supramarginal Gyrus Is Important for Proprioception in Healthy and Stroke-Affected Participants: A Functional MRI Study

Human proprioception is essential for motor control, yet its central processing is still debated. Previous studies of passive movements and illusory vibration have reported inconsistent activation patterns related to proprioception, particularly in high-order sensorimotor cortices. We investigated brain activation specific to proprioception, its laterality, and changes following stroke. Twelve healthy and three stroke-affected individuals with proprioceptive deficits participated. Proprioception was assessed clinically with the Wrist Position Sense Test, and participants underwent functional magnetic resonance imaging scanning. An event-related study design was used, where each proprioceptive stimulus of passive wrist movement was followed by a motor response of mirror -copying with the other wrist. Left (LWP) and right (RWP) wrist proprioception were tested separately. Laterality indices (LIs) were calculated for the main cortical regions activated during proprioception. We found proprioception-related brain activation in high-order sensorimotor cortices in healthy participants especially in the supramarginal gyrus (SMG LWP z = 4.51, RWP z = 4.24) and the dorsal premotor cortex (PMd LWP z = 4.10, RWP z = 3.93). Right hemispheric dominance was observed in the SMG (LI LWP mean 0.41, SD 0.22; RWP 0.29, SD 0.20), and to a lesser degree in the PMd (LI LWP 0.34, SD 0.17; RWP 0.13, SD 0.25). In stroke-affected participants, the main difference in proprioception-related brain activation was reduced laterality in the right SMG. Our findings indicate that the SMG and PMd play a key role in proprioception probably due to their role in spatial processing and motor control, respectively. The findings from stroke--affected individuals suggest that decreased right SMG function may be associated with decreased proprioception. We recommend that clinicians pay particular attention to the assessment and rehabilitation of proprioception following right hemispheric lesions.

A study of phonomicrosurgical arm support postures using a magnetic motion tracking system

OBJECTIVES/HYPOTHESIS

To study the different arm support postures used in phonomicrosurgery by using a magnetic-based phonomicrosurgery instrument tracking system (MPTS). Through quantitative motion parameter data collected from four arm support postures (elbow support [ES], forearm support [FS], forearm and hand support, and no support), phonomicrosurgical operation postures were analyzed and compared.

STUDY DESIGN

Prospective cohort study.

METHODS

Seven subjects operated on phonomicrosurgical simulation cutting tasks with four arm support postures while being monitored by MPTS. The motion parameters, including operation time, path length, depth perception, and motion smoothness were analyzed. The subjects' cutting quality was also calculated.

RESULTS

With the FS, the nondominant hand showed improved S, better D, and shorter P (P < 0.05). Better motion control in the dominant hand resulted from ES posture (P < 0.05). Better operation quality was associated with increased motion control in the nondominant hand.

CONCLUSIONS

Forearm support resulted in higher steadiness and shorter surgical path in the nondominant hand. In the dominant hand, ES resulted in increased steadiness, shorter surgical path, and better D. The effect of both gravity and wrist dexterity on movement control should be considered when selecting proper arm supports.

LEVEL OF EVIDENCE

4.

Noise-Enhanced Vestibular Input Improves Dynamic Walking Stability in Healthy Subjects

BACKGROUND

White noise galvanic vestibular stimulation (GVS) is thought to enhance the sensitivity of vestibular organs.

OBJECTIVE

To examine the effects of noise-enhanced vestibular input on the walking performance in healthy subjects walking with eyes closed.

METHODS

Walking performance of 17 healthy subjects (mean age 28.8 ± 1.7 years) at slow, preferred, and fast speeds was examined during three different conditions: (1) walking with eyes open (EO) as baseline condition, (2) walking with eyes closed and sham noisy GVS (EC), and (3) walking with eyes closed and non-zero amplitude noisy GVS set to 80% of the individual sensory threshold for GVS (EC-GVS). Ten gait parameters were examined: stride time, stride length, base of support, swing time percentage, double support time percentage as well as gait asymmetry, bilateral phase coordination and the coefficient of variation (CV) of stride time, stride length and base of support.

RESULTS

Noisy GVS improved stride time CV by 36% (p < 0.034), stride length CV by 31% (p < 0.037), base of support CV by 14% (p < 0.009), and bilateral phase coordination by 23% (p < 0.034). The ameliorating effects of noisy GVS on locomotion function were primarily observable during slow walking speeds.

CONCLUSION

Noise-enhanced vestibular input is effective in improving locomotion function and is accompanied by a subjectively felt improvement of walking balance. It predominantly targets the variability and bilateral coordination characteristics of the walking pattern, which are critically linked to dynamic walking stability. Noisy GVS might present an effective treatment option to improve walking performance in patients with bilateral vestibular dysfunction.

Functional impact of vibratory proprioceptive assistance in patients with facioscapulohumeral muscular dystrophy

INTRODUCTION

In this study we analyzed the effects of a rehabilitation method based on the use of vibratory proprioceptive assistance (VPA) in subjects with facioscapulohumeral muscular dystrophy.

METHODS

Eight subjects were given 1 month of mechanical vibratory treatment that consisted of 8 sessions of 40-min stimulation on the more affected side. During each session, illusory movements were induced as follows: sensations of extension or flexion of the forearm or elevation of the arm via vibration applied to the distal tendon of the biceps brachialis (BB), triceps brachialis (TB), or pectoralis major muscles (PM), respectively, and of elevation of the arm with extension or flexion of the forearm via vibration of PM+BB or PM+TB, respectively.

RESULTS

Treatment led to a significant increase in the amplitude of voluntary shoulder flexion, constant score, and self-rated health.

CONCLUSION

VPA may serve as a rehabilitation method for reducing the deleterious effects of decline in motor activities.

Effects of a Single Hand-Exercise Session on Manual Dexterity and Strength in Persons with Parkinson Disease: A Randomized Controlled Trial

OBJECTIVE

To evaluate the effects on manual dexterity, hand grip, and pinch strength of a single intervention focused on hand exercises.

DESIGN

Randomized, controlled, blinded study.

PATIENTS

Sixty people with Parkinson disease (PD) were recruited; 30 participants were allocated to a brief exercise session and 30 to a control group.

INTERVENTIONS

Participants randomized to the experimental group received a 15-minute exercise session focused on hand training using therapeutic putty. Participants allocated to the control group performed active upper limb exercises.

MAIN OUTCOME MEASUREMENTS

Measures of manual dexterity (assessed by the Purdue Pegboard Test and the Chessington Occupational Therapy Neurologic Assessment Battery dexterity task) and strength (hand grip and pinch strength) were recorded at baseline and after the intervention.

RESULTS

Participants had significantly improved manual dexterity values (P < .05) after the intervention. They also had increased hand grip (P < .001) and pinch strength (P < .05).

CONCLUSIONS

A single hand-exercise session showed an improvement in manual dexterity and strength in persons with PD.

Sensorimotor function of the cervical spine in healthy volunteers

BACKGROUND

Sensorimotor mechanisms are important for controlling head motion. However, relatively little is known about sensorimotor function in the cervical spine. This study investigated how age, gender and variations in the test conditions affect measures of position sense, movement sense and reflex activation in cervical muscles.

METHODS

Forty healthy volunteers (19M/21F, aged 19-59 years) participated. Position sense was assessed by determining repositioning errors in upright and flexed neck postures during tests performed in 25%, 50% and 75% cervical flexion. Movement sense was assessed by detecting thresholds to passive flexion and extension at velocities between 1 and 25°s(-1). Reflexes were assessed by determining the latency and amplitude of reflex activation in trapezius and sternocleidomastoid muscles. Reliability was evaluated from intraclass correlation coefficients.

FINDINGS

Mean repositioning errors ranged from 1.5° to 2.6°, were greater in flexed than upright postures (P=0.006) and in people aged over 25 years (P=0.05). Time to detect head motion decreased with increasing velocity (P<0.001) and was lower during flexion than extension movements (P=0.002). Reflexes demonstrated shorter latency (P<0.001) and greater amplitude (P=0.009) in trapezius compared to sternocleidomastoid, and became slower and weaker with age. None of the measures were influenced by gender. Reliability was good for movement sense measures, but was influenced by the test conditions when assessing position sense.

INTERPRETATION

Increased repositioning errors and slower reflexes in older subjects suggest that sensorimotor function in the cervical spine becomes impaired with age. In position sense tests, reliability was influenced by the test conditions with mid-range flexion movements, performed in standing, providing the most reliable measurements.

Assessing Proprioception: A Systematic Review of Possibilities

Proprioception is a vital aspect of motor control and when degraded or lost can have a profound impact on function in diverse clinical populations. This systematic review aimed to identify clinically related tools to measure proprioceptive acuity, to classify the construct(s) underpinning the tools, and to report on the clinimetric properties of the tools. We searched key databases with the pertinent search terms, and from an initial list of 935 articles, we identified 57 of relevance. These articles described 32 different tools or methods to quantify proprioception. There was wide variation in methods, the joints able to be tested, and the populations sampled. The predominant construct was active or passive joint position detection, followed by passive motion detection and motion direction discrimination. The clinimetric properties were mostly poorly evaluated or reported. The Rivermead Assessment of Somatosensory Perception was generally considered to be a valid and reliable tool but with low precision; other tools with higher precision are potentially not clinically feasible. Clinicians and clinical researchers can use the summary tables to make more informed decisions about which tool to use to match their predominant requirements. Further discussion and research is needed to produce measures of proprioception that have improved validity and utility.

Sensorimotor control during peripheral muscle vibration: an experimental study

OBJECTIVE

The aims of this study were to determine whether the application of vibration on a postural lower limb muscle altered the sensorimotor control of its joint as measured by isometric force production parameters and to compare present findings with previous work conducted on trunk muscle.

METHODS

Twenty healthy adults were asked to reproduce submaximal isometric plantar flexion under 3 different conditions: no vibration and vibration frequencies of 30 and 80 Hz on the soleus muscle. Time to peak torque, variable error, as well as constant error and absolute error in peak torque were calculated and compared across conditions.

RESULTS

Under vibration, participants were significantly less accurate in the force reproduction task, as they mainly undershot the target torque. Applying an 80-Hz vibration resulted in a significantly higher negative constant error than lower-frequency vibration (30 Hz) or no-vibration condition. Decreases in isometric force production accuracy under vibration influence were also observed in a previous study conducted on trunk muscle. However, no difference in constant error was found between 30- and 80-Hz vibration conditions.

CONCLUSION

The results suggest that acute soleus muscle vibration interferes with plantar flexion torque generation by distorting proprioceptive information, leading to decreases in accuracy of a force reproduction task. Similar results in an isometric trunk extension force reproduction task were found with vibration applied on erector spinae muscle. However, high-frequency vibration applied on soleus muscle elicited higher force reproduction errors than low-frequency stimulation.

A survey of manual preference, skill and strength in undergraduates

Objective: To examine hand preference, hand skill and hand strength in university undergraduates in order to determine the most reliable index of handedness.

Method: The Edinburgh Inventory, a group test of handedness by marking dots in circles, and a standard dynamometer were used with 248 (148 female, 100 male) subjects.

Results: No statistically significant correlations were found between hand skill and strength, or between hand preference and strength. A significant correlation between skill and preference was found in the male right-handed group of 93 students.

Conclusion: It is not possible to demonstrate whether preference or skill is the better index of handedness; a standardised method for assessment of hemispheric dominance for handedness is required; in the meantime the criterion used in a specific study should be explicitly stated in any citation of that study.

Sensory loss and walking speed related factors for gait alterations in patients with peripheral neuropathy

BACKGROUND

Walking instability and a higher risk of falls are common in patients with peripheral neuropathy. However, it remains uncertain as to whether alterations in neuropathic gait are directly related to deficient sensory locomotion control or due to a slowing of walking speed. By means of a multi-speed gait assessment we determined factors related to sensory loss and walking speed that cause changes in the gait pattern of neuropathic patients.

METHODS

Walking patterns of 18 neuropathic patients (70.7±2.4 years, 6 females) and 18 age- and gender-matched healthy subjects (70.4±2.4 years, 6 females) were recorded on a pressure-sensitive gait carpet for three different locomotion speeds (i.e. slow, preferred and fast) and while walking with eyes closed. Mean temporospatial gait parameters and gait variability were analyzed. The relationship between gait alterations and the history of falls in patients was evaluated.

RESULTS

Alterations in the mean locomotion pattern of neuropathic patients were mainly related to reduced walking speed. However, prolonged double support times (p<0.001), widened base widths (p=0.001) and increased gait variability (p<0.001) during slow walking or with eyes closed appeared to be directly linked to peripheral sensory loss in patients. Increased gait variability was predictive for the presence of self-reported falls in the past (p=0.029).

CONCLUSIONS

Sensory-loss-related prolongation of double support phases in neuropathic patients suggests a compensatory strategy to improve restabilization during locomotion. Moreover, widened base widths and increased gait variability point to an increased risk of falls. They occur primarily when patients are forced to reduce their walking speed or when visual feedback is disturbed.

Sense of effort revisited: relative contributions of sensory feedback and efferent copy

Although controversial, muscular effort perception is frequently attributed to the efferent copy of the associated motor command. While peripheral/sensory information is thought to be necessary for force modulation/control, it is not involved in initial force production. We recently showed in right-handers, that perception of effort was asymmetric for grasp-force tasks. This asymmetry was related to individual differences in right and left hand strength and an intrinsic component. A difference in gain (input/output magnitude relationship) for each limb/hemisphere system was proposed as the mechanism explaining intrinsic asymmetries. To further investigate the relative contributions of efferent copy and sensory feedback to the sense of effort, vibration was used to distort sensory information from the muscles providing the reference force. Visual feedback (vision) of the reference hand force was also manipulated. The absolute error (AE) was generally larger in the vision than no-vision condition and the influence of reference hand vibration was significant for left hand matching of the right hand reference force. However, this effect was negligible when matching in the reverse condition. These two results may reflect an interaction between two phenomena: (1) visual feedback, which represents the total output force may not be congruent with the internal representation of effort associated with the efferent copy and eventually the proprioceptive feedback; and (2) a vibration-induced larger AE for left than right hand contralateral matching indicates that the contribution of proprioceptive feedback to force matching is significant for the left but not the right hand/hemisphere system. Overall, it may be suggested that in right-handers, the sense of effort associated with the right hand may be primarily based on the efferent copy while the left hand/hemisphere system may use a combination of efferent copy and proprioceptive feedback. However, the weight of each type of information may depend on the association between motor command and representation of the execution of the motor command (visual vs. internal).

Modelling muscle spindle dynamics for a proprioceptive prosthesis

Muscle spindles are found throughout our skeletal muscle tissue and continuously provide us with a sense of our limbs' position and motion (proprioception). This paper advances a model for generating artificial muscle spindle signals for a prosthetic limb, with the aim of one day providing amputees with a sense of feeling in their artificial limb. By utilising the Opensim biomechanical modelling package the relationship between a joint's angle and the length of surrounding muscles is estimated for a prosthetic limb. This is then applied to the established Mileusnic model to determine the associated muscle spindle firing pattern. This complete system model is then reduced to allow for a computationally efficient hardware implementation. This reduction is achieved with minimal impact on accuracy by selecting key mono-articular muscles and fitting equations to relate joint angle to muscle length. Parameter values fitting the Mileusnic model to human spindles are then proposed and validated against previously published human neural recordings. Finally, a model for fusimotor signals is also proposed based on data previously recorded from reduced animal experiments.

Decreased skin temperature of the foot increases gait variability in healthy young adults

We investigated the effects of reduction in plantar skin temperature on gait. Thirty-four healthy subjects (20 men and 14 women; mean age 22.2±2.5 years; mean height 166.8±8.3cm) walked 16m under two different conditions - normal conditions (NC) with the skin at a basal temperature, and cold conditions (CC) after cooling of the plantar skin to about 15°C. Wireless motion-recording sensor units were placed on the back at the level of L3 and on both heels to measure acceleration and angular velocity. Gait velocity and mean stride, stance and swing times were calculated. The variability of lower limb movement was represented by the coefficients of variation (CVs) of stride, stance and swing times, and that of trunk movement was represented by autocorrelation coefficients (ACs) in three directions (vertical: VT; mediolateral: ML; and anteroposterior: AP). Gait velocity was significantly lower under CC conditions than under NC (p<0.0001). None of the temporal parameters were changed by plantar cooling. However, all parameters of gait variability were significantly worse under CC, and AC-VT, AC-ML, and AC-AP were significantly lower under CC than under NC, even after adjusting for gait velocity (p=0.0005, 0.0071, and 0.0126, respectively). Our results suggest that reducing plantar skin temperature induces gait variability among healthy young adults. Further studies are now needed to explore the relationship between plantar skin temperature and gait in the elderly.

An energy-efficient, dynamic voltage scaling neural stimulator for a proprioceptive prosthesis

This paper presents an 8 channel energy-efficient neural stimulator for generating charge-balanced asymmetric pulses. Power consumption is reduced by implementing a fully-integrated DC-DC converter that uses a reconfigurable switched capacitor topology to provide 4 output voltages for Dynamic Voltage Scaling (DVS). DC conversion efficiencies of up to 82% are achieved using integrated capacitances of under 1 nF and the DVS approach offers power savings of up to 50% compared to the front end of a typical current controlled neural stimulator. A novel charge balancing method is implemented which has a low level of accuracy on a single pulse and a much higher accuracy over a series of pulses. The method used is robust to process and component variation and does not require any initial or ongoing calibration. Measured results indicate that the charge imbalance is typically between 0.05%-0.15% of charge injected for a series of pulses. Ex-vivo experiments demonstrate the viability in using this circuit for neural activation. The circuit has been implemented in a commercially-available 0.18 μm HV CMOS technology and occupies a core die area of approximately 2.8 mm(2) for an 8 channel implementation.

The impact of rotator cuff tendinopathy on proprioception, measuring force sensation

BACKGROUND

The impact of rotator cuff tendinopathy and related impingement on proprioception is not well understood. Numerous quantitative and qualitative changes in shoulder muscles have been shown in patients with rotator cuff tendinopathy. These findings suggest that control of force might be affected. This investigation wants to evaluate force sensation, a submodality of proprioception, in patients with rotator cuff tendinopathy.

METHODS

Thirty-six patients with rotator cuff tendinopathy and 30 matched healthy subjects performed force reproduction tests to isometric external and internal rotation to investigate how accurately they could reproduce a fixed target (50% MVC). Relative error, constant error, and force steadiness were calculated to evaluate respectively magnitude of error made during the test, direction of this error (overshoot or undershoot), and fluctuations of produced forces.

RESULTS

Patients significantly overshoot the target (mean, 6.04% of target) while healthy subjects underestimate the target (mean, -5.76% of target). Relative error and force steadiness are similar in patients with rotator cuff tendinopathy and healthy subjects. Force reproduction tests, as executed in this study, were found to be highly reliable (ICC 0.849 and 0.909). Errors were significantly larger during external rotation tests, compared to internal rotation.

CONCLUSION

Patients overestimate the target during force reproduction tests. This should be taken into account in the rehabilitation of patients with rotator cuff tendinopathy; however, precision of force sensation and steadiness of force exertion remains unaltered. This might indicate that control of muscle force is preserved.

Electrophysiological analysis of the perception of passive movement

The goal of the present study was to determine the electrophysiological correlate of the threshold of perception of passive motion (TPPM) in a group of healthy individuals. We expect a different pattern of activation over the frontoparietal network produced by the conscious perception of the passive movement. Ten right-handed male volunteers, between 20 and 30 years of age, were submitted to the threshold of perception of passive motion (TPPM) task in a proprioception testing device (PTD). The device was designed to passively move the arm in internal and external rotations about the shoulder joint. Participants were instructed to press a hand-held switch every time movement of the shoulder was detected. Electromyographic (EMG) and electroencephalographic (EEG) activities were acquired during the task. Passive movement of the shoulder joint was followed by a clear and prolonged decrease in the signal magnitude of the electroencephalogram. The electrophysiological correlate of the TPPM was characterized by the establishment of a frontoparietal network, during the processing of somatosensory information.

Embodied Emotion Perception

How do we recognize the emotions other people are feeling? One source of information may be facial feedback signals generated when we automatically mimic the expressions displayed on others' faces. Supporting this “embodied emotion perception,” dampening (Experiment 1) and amplifying (Experiment 2) facial feedback signals, respectively, impaired and improved people’s ability to read others' facial emotions. In Experiment 1, emotion perception was significantly impaired in people who had received a cosmetic procedure that reduces muscular feedback from the face (Botox) compared to a procedure that does not reduce feedback (a dermal filler). Experiment 2 capitalized on the fact that feedback signals are enhanced when muscle contractions meet resistance. Accordingly, when the skin was made resistant to underlying muscle contractions via a restricting gel, emotion perception improved, and did so only for emotion judgments that theoretically could benefit from facial feedback.

Tactile spatial acuity is reduced by skin stretch at the human wrist

The skin is an elastic organ that is continuously distorted as our limbs move. The hypothesis that the precision of human tactile localisation is reduced when the skin is stretched, with concurrent expansion of receptive fields (RFs) was tested. Locognosic acuity over the dorsal wrist area was quantified during application of background stretch by (a) Wrist-Bend (skin stretch combined with non-cutaneous proprioceptor activation) and (b) Skin-Pull (skin stretch alone). Participants identified the perceived direction (distal or proximal) of brief test stimuli, applied along a 7-point linear array, relative to a central reference locus. Performance was significantly reduced during the large amplitude compared to the small amplitude of tonic skin stretch, but there was no effect of stretch mode (Wrist-Bend, Skin-Pull), nor was the effect of stretch amplitude modulated by the mode of stretch. Locognosic acuity was poorer than baseline accuracy for the large amplitude skin stretches, for both application modes, but did not differ significantly from baseline for either of the small amplitude stretches. We interpret these observations as corroborating the long-held assumption that tactile localisation is primarily dependent upon the RF dimensions, and associated innervation densities, of regional touch units. The finding that performance was reduced to a similar extent under Skin-Pull and Wrist-Bend conditions suggests that non-cutaneous proprioceptors had rather little tonic modulatory effect.

Concordância inter-observador em testes de avaliação proprioceptiva do joelho por goniometria

O propósito deste foi determinar o grau de concordância inter-avaliador de dois testes que mensuram a propriocepção do joelho por meio da goniometria, em uma amostra de universitárias (n=13; 23,8±6,4 anos). Mensurou-se a acurácia proprioceptiva pelos testes de percepção do limiar de movimento passivo lento (T1), movendo-se passivamente a perna até o ângulo alvo; e pelo teste de senso de posição articular (T2), solicitando-se movimento ativo até o ângulo alvo, previamente atingido passivamente. Os ângulos alvos foram sorteados e as medições feitas simultaneamente, de forma cega, por dois avaliadores, por meio de dois goniômetros idênticos posicionados nas faces medial e lateral do joelho. As participantes sinalizavam ao atingir o ângulo alvo, registrando-se, por ambos os avaliadores, os valores angulares efetivamente alcançados. A diferença (em números absolutos) entre o ângulo alvo e aquele alcançado foi considerada o "valor de erro", que reflete a acuidade proprioceptiva. Determinou-se a concordância inter-avaliador pelo teste de concordância de Kappa; os valores encontrados (T1, Kappa=0,55; T2, Kappa=0,58) mostram concordância moderada. Como a concordância inter-avaliador nos dois testes foi moderada, conclui-se que a goniometria é limitada, na avaliação proprioceptiva de movimento do joelho.

What does body configuration in microgravity tell us about the contribution of intra- and extrapersonal frames of reference for motor control?

The authors report that the reorganization of body configuration during weightlessness is based on an intrapersonal frame of reference such as the configuration of the support surface and the position of the body's center of gravity. These results stress the importance of “knowledge” of the state of internal geometric structures, which cannot be directly signalled by specific receptors responsible for direct dialogue with the physical external world.

Reciprocal and coactivation commands are not sufficient to describe muscle activation patterns

Recent results have shown that the relative activation of muscles is different for isometric contractions and for movements. These results exclude an explanation of muscle activation patterns by a combination ofreciprocal and coactivation commands. These results also indicate that joint stiffness is not uniquely determined and that it may be different for isometric contractions and movements.

Frames of reference interact and are task-dependent

The problem for the CNS in any particular movement task is to coordinate the various frames of reference appropriate to the task. Control variables are determined by this coordination. The coordination problem varies greatly from task to task, and so no single set of control variables is likely to account for a broad range of movement tasks.

Temporal representation in the control of movement

Theories of the representation of specific kinetic and spatiotem-poral features of movement range from the explicit assertion that temporal aspects of movement are not represented (Kugler et al. 1980) to the idea that they are represented and that they have neurophysiological correlates (Ivry & Corcos 1993; Ivry & Keele 1989). Jeannerod's thesis is that mental and visual images have common mechanisms and that there is a link between the image to move and the mechanisms involved with movement. The target article takes the position that certain parameters are coded in motor representations (sect. 4) but that the duration of an action is not one of them. This position is based on the work of Gottlieb et al. (1989b) and of Decety et al. (1989). Both these studies are worth considering in detail. In Note 1, Jeannerod suggests that: “in time-constrained tasks subjects control the amplitude parameter of force impulses, whereas in spatially constrained tasks the duration of the force impulse is affected by accuracy demands.” This is not exactly correct. Excitation pulse intensity (amplitude) is modulated both in tasks that require spatial and those that require temporal accuracy. Excitation pulse duration is modulated for changes in movement distance and inertial load. If subjects are required to be very accurate spatially, they will move at less than maximum speed for a given distance and this is achieved by lower levels of excitation intensity (Gottlieb et al. 1990).

The λ model for motor control: More than meets the eye

Understanding of the λ model has greatly increased in recent years as evidenced by most of the commentaries. Some commentators underscored the potential of the model to integrate aspects of different sensorimotor systems in the production of movement. Other commentators focused on not-yet-fully-developed parts of the model. A few persisted in misunderstanding some of its basic concepts, and on these grounds they reject it. In responding to commentaries we continue to elaborate on some fundamental points of the model, especially control variables, the idea of movement production by shifting the positional frame of reference and the hypothesis of biomechanical correspondence in motor control. We also continue to develop our ideas on the intrinsic generation of the frame of reference associated with external space and utilized for the control of arm movement and locomotion. The dynamic principles underlying the model are discussed in light of the dynamical systems approach.

Grip force adjustments during rapid hand movements suggest that detailed movement kinematics are predicted

The λ model suggests that detailed kinematics arise from changes in control variables and need not be explicitly planned. However, we have shown that when moving a grasped object, grip force is precisely modulated in phase with acceleration-dependent inertial load. This suggests that the motor system can predict detailed kinematics. This prediction may be based on a forward model of the dynamics of the loaded limb.