The proprioceptive senses: their roles in signaling body shape, body position and movement, and muscle force

Movement control of the cervical spine declines with aging: a cross-sectional study

BACKGROUND

Previous studies suggest that cervical spine position sense declines with age, while the relationship between aging and cervical spine movement control remains unknown.

OBJECTIVE

To investigate the relationship between age and cervical spine movement control in asymptomatic adults.

METHODS

One hundred five asymptomatic adults (21-79 years old) were included. The Butterfly test (performed with an inertial measurement unit) was used to assess movement control of the cervical spine, in which participants tracked an unpredictable moving target with active head and neck movements at three different movement path difficulty levels (3 repetitions each). The determined parameters were amplitude accuracy (AA), time on target (ToT), undershoot (U) and overshoot (O). Spearman's rank correlation coefficient and simple linear regression analysis were used to assess the relationship between age and each parameter.

RESULTS

A significant relationship was demonstrated between advancing age and the AA, ToT and U parameters for all three movement path difficulty levels (p ≤ .001), but not for the O parameter (p > .05). Advancing age explained 19.8-30.4%, 24.5-30.8% and 33.7-37.2% of the variance in the AA, ToT, and U parameters, respectively.

CONCLUSION

The results suggest that cervical spine movement control declines with aging in an asymptomatic population. Clinicians may need to monitor potential deficits in cervicocephalic kinesthesia in older asymptomatic adults, as these impairments may have a considerable impact on their functional abilities.

Integrating deliberate shaking into daily living: a paradoxical exercise for Parkinsonian tremor

PURPOSE

Medication often falls short in controlling tremors in Parkinson's disease. While physical activities suggest potential benefits, current exercise regimes have limitations. This paper explores the concept of deliberate shaking as an intervention to aid exercise uptake and potentially leverage synergies between medication and physical activity. It examines the rationale for and mechanisms of deliberate shaking before exploring its further examination and implementation for tremor rehabilitation.

METHOD

This conceptual article draws on relevant literature using the SANRA guide to explore the potential of deliberate shaking to relieve tremors in Parkinson's disease.

RESULTS

Deliberate shaking is a controlled exercise where an individual consciously initiates and partially surrenders to rhythmic movements while maintaining the ability to stop at will. Integrated into daily activities, this practice may target and stimulate specific muscle groups. It may alleviate tremor through various mechanisms: neurobiological, physiological, and cognitive and psychological. Before implementation, empirical research is needed to assess its feasibility, safety, and effectiveness. Implementation requires assessing eligibility for a shaking prescription, setting personalized goals, providing guidance as needed, and ensuring appropriate safety measures are in place.

CONCLUSIONS

Deliberate shaking is a potential adjunct treatment for Parkinsonian tremor. However, it requires further testing.

Insights into proprioceptive acuity assessed with a dynamic joint position reproduction task

This study investigated proprioceptive acuity using the conventional joint position reproduction (JPR) task and a modified version, the Dynamic JPR task (D-JPR), during Concentric and Eccentric muscle contractions. Seventeen participants were recruited and received a tactile stimulus indicating the position cue at Initial (INI), Intermediate (INT), and Final (FIN) phases of movements, during either the concentric or eccentric phases. After the movement, they replicated the position where they received the stimulus. Angular error (AE) and movement velocity were analysed. AE was higher in the D-JPR than in JPR Task, and in Concentric than Eccentric contractions. Within the D-JPR Task, during Concentric contractions, AE was lower at FIN phase compared to INI and INT phases, and at INT phase compared to INI phase, whereas in Eccentric contraction AE was lower in FIN compared to INI phase. Significant correlations between movement velocity at the time of stimulus delivery and AE were found in both types of contractions. Proprioceptive acuity was affected by task type, muscle contraction, movement phase, and movement velocity, highlighting the need to consider these factors for accurate and ecological assessments of proprioception.

Differential encoding of mammalian proprioception by voltage-gated sodium channels

Animals requiring purposeful movement for survival are endowed with mechanoreceptors, called proprioceptors, that provide essential sensory feedback from muscles and joints to spinal cord circuits, which modulates motor output. Despite the essential nature of proprioceptive signaling in daily life, the mechanisms governing proprioceptor activity are poorly understood. Here, we identified nonredundant roles for two voltage-gated sodium channels (NaVs), NaV1.1 and NaV1.6, in mammalian proprioception. Deletion of NaV1.6 in somatosensory neurons (NaV1.6cKO mice) causes severe motor deficits accompanied by loss of proprioceptive transmission, which contrasts with our previous findings using similar mouse models to target NaV1.1 (NaV1.1cKO). In NaV1.6cKO animals, we observed impairments in proprioceptor end-organ structure and a marked reduction in skeletal muscle myofiber size that were absent in NaV1.1cKO mice. We attribute the differential contributions of NaV1.1 and NaV1.6 to distinct cellular localization patterns. Collectively, we provide evidence that NaVs uniquely shape neural signaling within a somatosensory modality.

Effect of proprioceptive neuromuscular facilitation on patients with chronic ankle instability: A systematic review and meta-analysis

OBJECTIVE

This study conducts a rigorous meta-analysis of existing literature to rigorously examine the efficacy of Proprioceptive Neuromuscular Facilitation (PNF) in ameliorating functional deficits associated with Chronic Ankle Instability (CAI).

METHODS

Literature searches were conducted in multiple databases including China National Knowledge Infrastructure (CNKI), VIP, Wanfang, China Biology Medicine disc (CBM), PubMed, EBSCO (Medline, CINAHL, SPORTDiscus, and Rehabilitation & Sports Medicine Source), Embase, ScienceDirect, ProQuest, Cochrane Library, and Web of Science for randomized controlled trials assessing the effects of Proprioceptive Neuromuscular Facilitation interventions on patients with Chronic Ankle Instability. The publication timeframe spanned from the inception of each database until April 10, 2024. Meta-analysis was performed using STATA 12 software on the included studies.

RESULTS

① A total of 12 randomized controlled trials were included, encompassing 405 patients with Chronic Ankle Instability, demonstrating a generally high methodological quality of the literature.② Meta-analysis results indicate that compared to the control group, Proprioceptive Neuromuscular Facilitation (PNF) significantly enhanced the balance ability of patients with Chronic Ankle Instability as measured by the Y Balance Test (YBT) (Weighted Mean Difference (WMD) = 3.61, 95% CI [2.65, 4.56], z = 7.42, P<0.001) and the Star Excursion Balance Test (SEBT) (WMD = 5.50, 95% CI [3.80, 7.19], z = 6.36, P<0.001), with improvement in all eight directions of SEBT balance ability surpassing that of the control group (P<0.05); muscle strength around the ankle (SMD) = 0.19, 95% CI [0.03, 0.36], z = 2.26, P = 0.024), with both Plantar flexion and Dorsal flexion muscle strength improvements exceeding those of the control group (P<0.05); Visual Analog Scale (VAS) (WMD = -1.39, 95% CI [-1.72, -1.06], z = 8.23, P<0.001); Ankle instability questionnaire (WMD = 2.91, 95% CI [1.92, 3.89], z = 5.78, P<0.001).③Descriptive analysis results showed that the differences in Inversion Joint Position Sense and Dorsiflexion range of motion between the PNF and control groups were not statistically significant (P>0.05), however, the effects of PNF training persisted for a certain period even after cessation of treatment.

CONCLUSION

Proprioceptive Neuromuscular Facilitation (PNF) can significantly improve balance, muscle strength, and pain in patients with Chronic Ankle Instability (CAI). While PNF has shown improvements in joint position sense and dorsiflexion range of motion for CAI patients, with effects that remain for a period thereafter, these improvements were not significantly different when compared to the control group. Further research is required to substantiate these specific effects.

Human motor performance assessment with lower limb exoskeletons as a potential strategy to support healthy aging-a perspective article

With increasing age, motor performance declines. This decline is associated with less favorable health outcomes such as impaired activities of daily living, reduced quality of life, or increased mortality. Through regular assessment of motor performance, changes over time can be monitored, and targeted therapeutic programs and interventions may be informed. This can ensure better individualization of any intervention approach (e.g. by considering the current motor performance status of a person) and thus potentially increase its effectiveness with regard to maintaining current performance status or delaying further decline. However, in older adults, motor performance assessment is time consuming and requires experienced examiners and specific equipment, amongst others. This is particularly not feasible in care facility/nursing home settings. Wearable robotic devices, such as exoskeletons, have the potential of being used to assess motor performance and provide assistance during physical activities and exercise training for older adults or individuals with mobility impairments, thereby potentially enhancing motor performance. In this manuscript, we aim to (1) provide a brief overview of age-related changes of motor performance, (2) summarize established clinical and laboratory test procedures for the assessment of motor performance, (3) discuss the possibilities of translating established test procedures into exoskeleton-based procedures, and (4) highlight the feasibility, technological requirements and prerequisites for the assessment of human motor performance using lower limb exoskeletons.

Versatile graceful degradation framework for bio-inspired proprioception with redundant soft sensors

Reliable proprioception and feedback from soft sensors are crucial for enabling soft robots to function intelligently in real-world environments. Nevertheless, soft sensors are fragile and are susceptible to various damage sources in such environments. Some researchers have utilized redundant configuration, where healthy sensors compensate instantaneously for lost ones to maintain proprioception accuracy. However, achieving consistently reliable proprioception under diverse sensor degradation remains a challenge. This paper proposes a novel framework for graceful degradation in redundant soft sensor systems, incorporating a stochastic Long Short-Term Memory (LSTM) and a Time-Delay Feedforward Neural Network (TDFNN). The LSTM estimates readings from healthy sensors to compare them with actual data. Then, statistically abnormal readings are zeroed out. The TDFNN receives the processed sensor readings to perform proprioception. Simulation experiments with a musculoskeletal leg that contains 40 nonlinear soft sensors demonstrate the effectiveness of the proposed framework. Results show that the knee angle proprioception accuracy is retained across four distinct degradation scenarios. Notably, the mean proprioception error increases by less than 1.91°(1.36%) when 30 % of the sensors are degraded. These results suggest that the proposed framework enhances the reliability of soft sensor proprioception, thereby improving the robustness of soft robots in real-world applications.

Useful and Useless Misnomers in Motor Control

This article addresses the issue of using terms and concepts in motor control that are ill-defined, undefined, and/or imported from nonbiological fields. In many of such cases, the discourse turns nonscientific and unproductive. Some of such terms are potentially useful but need to be properly and exactly defined. Other terms seem to be misleading and nonfixable. There is also an intermediate group with terms that may or may not be useful if defined properly. The paper presents three examples per group: "reflex," "synergy," and "posture" versus "motor program," "efference copy," and "internal model" versus "muscle tone," "stiffness and impedance," and "redundancy." These terms are analyzed assuming that motor control is a branch of natural science, which must be analyzed using laws of nature, not a subfield of the control theory. In the discussion, we also accept the framework of the theory of movement control with spatial referent coordinates as the only example built on laws of nature with clearly formulated physical and physiological nature of the control parameters.

Force drifts and matching errors in the lower extremities: implications for the control and perception of foot force

Accurate control of force on the environment is mechanically necessary for many tasks involving the lower extremities. We investigated drifts in the horizontal (shear) active force produced by right-footed seated subjects and the effects of force matching by the other foot. Subjects generated constant shear force at 15% and 30% of maximal voluntary contraction (MVC) using one foot. Visual feedback of shear force magnitude was provided for the first 5s, then turned off for 30s. During the 30% MVC task, we observed parallel drops in active shear and vertical force magnitudes leading to consistent drifts in the resultant force magnitude, not in its direction. Force matching by the other foot resulted in significantly lower forces when feedback was available throughout the trial. No feedback was provided for the matching foot. When the matching foot began exerting force, the task foot experienced a notable drop in all force components, with a change in force direction only for the task foot. After this initial drop, the downward drift in the task foot stopped or reversed. Subjects were unaware of these drifts and errors. Our findings suggest that shear force production involves setting a referent coordinate vector, which shows drifts and matching errors, while its direction remains stable. Involvement of the matching foot appears to perturb the neural commands to the task foot, with minor differences observed between feet. The discrepancy between the consistent force drifts and lack of awareness of the drifts indicates a difference between force perception-to-act and perception-to-report.

Normative values of spinal and peripheral proprioception in position sense among healthy adolescents and young adults

Establishing normative values and understanding how proprioception varies among body parts is crucial. However, the variability across individuals, especially adolescents, makes it difficult to establish norms. This prevents further investigation into classifying patients with abnormal proprioception. Therefore, the primary objective was to address the knowledge gap using three-dimensional motion analysis to capture position sense in adolescents and young adults. The secondary objective was to evaluate the relationship between position sense and age, as well as the interrelationships of position senses across various anatomical sites. Healthy participants aged 10 to 25 years were included. Six position sense tests were implemented on the trunk, neck, elbow, and knee. Data were captured using a three-dimensional motion capture system. The proprioceptive measure was the absolute repositioning error (the difference between the destinated starting position and the corresponding self-reproduced ending position) of each test. A total of 103 participants were recruited. We found that only spinal proprioception was associated with chronological age, whereas peripheral proprioception was not. Subgroup analyses revealed that subjects aged 10 to 13 years had the poorest proprioceptive performance. The normative values of proprioception of various body parts were, trunk flexion-extension test = 25° ± 12°; trunk lateral-flexion test = 23° ± 10°; trunk axial-rotation test = 26° ± 11°; left neck rotation test = 2° ± 1°; right neck rotation test = 3° ± 1°; left elbow flexion test = 5° ± 3°; right elbow flexion test = 5° ± 2°; left knee extension test = 3° ± 2°; right knee extension test = 3° ± 1°. The normative values of proprioception in position sense provided in this study may help identify individuals with proprioceptive deficits and inform targeted interventions to improve proprioception.

Effect of concentric exercise-induced fatigue on proprioception, motor control and performance of the upper limb in handball players

BACKGROUND

The last phases of a competitive game are when shoulder injuries most commonly happen, and fatigue is thought to be a major contributing factor, perhaps because of reduced proprioception and motor control. The purpose of this study was to investigate the effect of concentric fatigue on proprioception, motor control, and performance of the upper limb in handball players.

METHODS

Forty-six right-handed handball players (all males, age 26.1 ± 5.54 years) were included in this test-retest laboratory experiment. Proprioception was assessed using joint reposition sense (JRS), threshold to detection of passive movement (TTDPM), muscle onset latency (MOL), motor control using Y balance test upper quarter (YBT-UQ) and performance using the athletic shoulder test (ASH) before and immediately after fatigue intervention. The fatigue protocol consisted of concentric, maximal effort, isokinetic contractions at 900/sec with sets of 30 repetitions of the shoulder external and internal rotator muscles. Fatigue was determined by a 40% decline in the peak torque over three consecutive contractions despite reinforcing feedback and encouragement.

RESULTS

A significant increase in absolute angular error (AAE) was observed in all target angles in both external rotation (ER) and internal rotation (IR) directions (p < 0.01). In addition, there was a significant increase in TTDPM in internal rotation after fatigue intervention (p = 0.020. Variable changes were found in YBT-UQ and ASH tests. Specifically, statistically significant differences were found in anteromedial (AM) (p = 0.041), superolateral (SL) reach directions (p = 0.005), composite score (p = 0.009) in the right hand and inferolateral (IL) reach direction in the left hand (p = 0.020) in the YBT-UQ. In addition, there was a significant reduction in isometric strength (ASH test) in the I position of the right hand (p = 0.010) and all positions of the left hand (p<0.05). Furthermore, there was an increase in MOL scores after fatigue but the increase was not significant (p > 0.05).

CONCLUSIONS

Concentric fatigue of the rotator cuff muscles induces notable deficits in joint position awareness, kinesthesia, motor control, and performance of the upper extremity in elite male handball players. Although fatigue reduces reflex reaction time the effect is only marginal.

Effects of attentional focus on spatial localization of distal body parts and touch in two-arm position matching

This study investigated how the judgment of proximal joint position can be affected by touch alone, focused attention on the distal body part, or touch spatial localization. Participants completed a two-arm elbow joint position-matching task, in which they indicated the location of one forearm by the placement of the other. In four test conditions, matching was performed during (1) detection of touch (tactile stimulation of index finger pads), (2) spatial localization of fingers (attention focused on the position of index finger pads), (3) spatial localization of touch on fingers (attention focused on tactile stimulation of index finger pads), and (4) detection of touch but localization of fingers (tactile stimulation of index finger pads, but attention focusing on the spatial position of the pads). In the first experiment (n = 23), the sensitivity of muscle spindle receptors in both reference and indicator arms was reduced and equalized by both-slack conditioning. In the second experiment (n = 20), the illusion of excessive elbow flexion in the reference arm and excessive extension in the indicator arm was generated through extension-flexion conditioning. In the first experiment, the accuracy and precision of matching were unaffected in any test condition. In the second experiment, participants made amplified undershooting errors under attention-focused conditions. In conclusion, focused attention on the location of a distal body part and touch affects both the spatial localization of the limb and tactile remapping only when the perceived forearm position is misinterpreted due to imbalanced proprioceptive input from antagonistic arm muscles.

The importance of recovering body awareness in post-stroke rehabilitation: insights from clinical case reports

Introduction

Body awareness (BA) is the process of gaining sensory awareness based on the physiological states and actions of the body. It is influenced by an individual's attitudes, perceptions, beliefs, and experiences within the social and cultural contexts. Following a stroke, impairments in BA are thought to be widespread and could have a significant impact on recovery results. Regaining body awareness, however, is often neglected in the neurorehabilitation field. This study aimed to assess body image perception in two stroke patients and the potential effect of motor and cognitive rehabilitative treatments on possible improvement of BA.

Methods

Patients were evaluated through a multidimensional neuropsychological assessment before and after a 3-month motor and cognitive rehabilitative training. Sessions were scheduled 6 times per week with a total duration of 3 h per session.

Results

After the neurorehabilitative treatment, both patients showed an improvement in BA, cognition, mood, and motor skills. Differences emerged related to the progression and improvement of their respective performances.

Discussion

The causes of these differences could include the following: different brain areas affected, the ischemic or hemorrhagic nature of the stroke, age, and sex. Further research is needed to better understand the differences and similarities in the correlations between deficit and lesional sites. Structured and early multidisciplinary intervention can certainly guarantee a better functional recovery for patients after a stroke. However, in this study we show how complementary assessment methods (such as human figure drawing) may be highly informative in choosing treatment modalities and verifying rehabilitation outcomes.

Sensory and Motor Function, Pain, and Health Status in Children with Arthrogryposis and Myelomeningocele

BACKGROUND/OBJECTIVES

Proprioception and sensory disorders have been reported in children with arthrogryposis multiplex congenita (AMC) and myelomeningocele (MMC), but valid and reliable assessment tools are limited in accurately identifying the sensory aspects of motor disorders. This study aimed to investigate the somatosensory status in the feet and legs. An additional purpose of this study was to explore pain, skin irritations, and health status.

METHODS

Nineteen children with AMC, twenty-three with MMC, and twenty-two typically developing (TD) children (7-18 years old) were tested using a somatosensory test battery in ankle kinesthesia and in identifying four different types of floors.

RESULTS

In the AMC and MMC groups, the threshold to perceive the somatosensory stimuli was not achieved by all participants. MMC participants perceived somatosensory stimuli less than TD participants in all tests, with a higher level of the lesion and more affected ambulation. The MMC group identified one floor significantly less often than the TD group. The AMC group performed better than the MMC group in two-point discrimination, vibration sensation, and some light-touch pressure tests. There were no differences among the TD, AMC, and MMC groups in ankle kinesthesia. Pain was reported by four (21%) subjects in the AMC group and five (22%) in the MMC group, and skin irritations were reported by three (13%) participants in the MMC group. There was no difference among the TD, AMC, and MMC groups in health status as reported using the EQ-5D-Y visual analog scale.

CONCLUSIONS

Although differences in sensory aspects were the most evident between the groups, assessments of activity and participation levels in the rehabilitation of children with disabilities are also recommended.

Cortical brain potentials in response to lower limb proprioceptive stimuli in young adults with probable developmental coordination disorder

BACKGROUND

Proprioceptive deficits have been shown to underlie motor problems in individuals with a probable developmental coordination disorder (pDCD). Behavioral studies have employed response times to passive limb movement to evaluate proprioceptive function in individuals with pDCD. However, the underlying neural mechanisms involved in the cortical processing of proprioceptive input and its corresponding motor response are unclear. To address this issue, this study aims to investigate neuropsychological and neurophysiological performances using event-related potentials (ERP) on proprioceptive-motor tasks in young adults with pDCD.

METHODS

From a total of 149 young adults screened using the Bruininks-Oseretsky Test of Motor Proficiency 2nd Edition Complete Form (BOT-2), 12 individuals with pDCD were identified (mean age ± SD: 20.50 ± 1.08 years) along with 12 age- and sex-matched controls (mean age ± SD: 20.75 ± 1.05 years). Participants placed their dominant foot on a passive ankle motion apparatus that plantarflexed the ankle at a constant velocity of 22°/s for a total of 75 trials in each proprioceptive condition. With vision occluded, participants had to press the trigger button held by the dominant hand when they sensed the passive motion of the ankle (voluntary response, VR), or purely receive the movement without a voluntary response (non-voluntary response, NVR). Behavioral performances [i.e., mean movement detection time (MDTmean), the standard deviation of the movement detection time (MDTSD)] and ERP indices (i.e., N1, P3 amplitude, and latency) related to ankle kinesthetic stimuli were obtained to determine the proprioceptive-motor function.

RESULTS

The results showed that young adults with pDCD exhibited longer MDTmean (p < 0.001) and MDTSD (p = 0.002) compared to their controls. Electrophysiological indices measured at frontal and central electrode sites, showed that young adults with pDCD exhibited significantly smaller N1 (p = 0.019) and P3 amplitudes (p = 0.032) during VR and NVR conditions. Notably, correlation analysis revealed a significant negative relationship between MDTmean and N1 (r = 0.62, p < 0.001) and P3 amplitudes (r = - 0.55, p = 0.005) in the VR condition in young adults with and without pDCD.

CONCLUSIONS

This study sheds light on the central brain mechanisms underlying proprioceptive-motor deficits in young adults with pDCD. The combined analysis of behavioral and ERP data suggests that longer MDTmean and larger MDTSD in young adults with pDCD are associated with weaker proprioceptive afferent inflow shown by decreased N1 amplitude to the frontal and parietal cortices. Such degraded proprioceptive signals are followed by reduced P3 amplitude, suggesting that young adults with pDCD allocate fewer neural resources to modulate motor processes with regard to proprioceptive stimuli. These findings contribute to a better understanding of the neurophysiological basis of proprioceptive-motor deficits in pDCD and may inform the development of targeted sensorimotor interventions.

The effect of age and proprioceptive illusion susceptibility on gait

OBJECTIVE

Age-related gait decline has been associated with impaired proprioception, one's internal awareness of spatial location and movement. Although impaired proprioception has further been linked to greater susceptibility to proprioceptive illusions, it is unclear the impact such susceptibility has on gait and its interaction with age. The purpose of this study was to address these uncertainties.

METHODS

We measured proprioceptive illusions induced by muscle spindle manipulation and gait in young and older adults. We also compared illusory measures with traditionally used joint position matching to examine if illusory susceptibility can reveal proprioceptive impairments.

RESULTS

We found no effect of age on proprioceptive illusion susceptibility or joint position matching error. Compared to non-perceivers, illusion perceivers across both age groups showed greater joint matching error, suggesting reduced proprioceptive acuity. Consistent with previous studies, older adults had reduced cadence, gait velocity, and step length compared to young adults in both single- and dual-task walking. Interestingly, illusion perceivers, regardless of age, showed reduced cadence and step width compared to non-perceivers.

CONCLUSIONS

Our results suggest that gait impairments observed in those who perceive these proprioceptive illusions are age-independent, potentially rooted in deteriorated proprioception.

SIGNIFICANCE

This is the first study to examine these relations.

Peripheral neuropathy, an independent risk factor for falls in the elderly, impairs stepping as a postural control mechanism: A case-cohort study

BACKGROUND/AIMS

Peripheral neuropathies perturbate the sensorimotor system, causing difficulties in walking-related motor tasks and, eventually, falls. Falls result in functional dependency and reliance on healthcare, especially in older persons. We investigated if peripheral neuropathy is a genuine risk factor for falls in the elderly and if quantification of postural control via posturography is helpful in identifying subjects at risk of falls.

METHODS

Seventeen older persons with a clinical polyneuropathic syndrome of the lower limbs and converging electrophysiology were compared with 14 older persons without polyneuropathy. All participants were characterized via quantitative motor and sensory testing, neuropsychological assessment, and self-questionnaires. Video-nystagmography and caloric test excluded vestibulocochlear dysfunction. For further analysis, all subjects were stratified into fallers and non-fallers. Overall, 28 patients underwent computerized dynamic posturography for individual fall risk assessment. Regression analyses were performed to identify risk factors and predictive posturography parameters.

RESULTS

Neuropathy is an independent risk factor for falls in the elderly, while no differences were observed for age, gender, weight, frailty, DemTect test, timed "Up & Go" test, and dizziness-related handicap score. In computerized dynamic posturography, fallers stepped more often to regain postural control in challenging conditions, while the Rhythmic Weight Shift test showed a lack of anterior-posterior bidirectional voluntary control.

INTERPRETATION

Our study confirms peripheral neuropathy as a risk factor for older persons' falls. Fallers frequently used stepping to regain postural control. The voluntary control of this coping movement was impaired. Further investigations into these parameters' value in predicting the risk of falls in the elderly are warranted.

Mid-vastus approach induces milder short-term effects on postural control compared to parapatellar approach in total knee arthroplasty

BACKGROUND

Mid-Vastus and Medial Parapatellar techniques are used for total knee arthroplasty. Their short-term effects within the first month after surgery are yet unexplored. The purpose of this study was to compare Mid-Vastus and Medial Parapatellar effects on knee strength and balance control, at 5 days, 2 weeks and one month after surgery. It was hypothesized that Mid-Vastus would induce milder effects on the dependent variables due to its less invasive nature.

METHODS

Twenty females, randomly assigned to either the Mid-Vastus or the Medial Parapatellar group performed knee flexion-extension force and 30 s of bipedal stance before, 5 days, 2 weeks and one month after surgery. Maximum force, weight distribution and travel distance of the Center of Pressure were calculated.

FINDINGS

Both groups showed decreased force output at all post-measurements compared to before surgery. Medial Parapatellar group showcased significantly higher travel distance at the 2 weeks measurement (Z = -2.268, p = .023, |r| = 0.507) compared to before surgery. This result was also imprinted on the travel distance of the non-surgical knee limb in the post (t = 3.259, p = .004, d = 1.456), 2 weeks (Z = -2.570, p = .009, |r| = 0.574) and one month measurement (t = 2.653, p = .016, d = 1.185).

INTERPRETATION

While force is affected for both approaches, Mid-Vastus approach does not affect postural control. Therefore, Mid-Vastus is a less invasive technique compared to Medial Parapatellar. This work highlights the differences between Mid-Vastus and Medial Parapatellar approaches at least until the first month of rehabilitation.

Serious Game-Based Balance Training with Augmented Kinesthetic Feedback Enhances Aspects of Postural Control in Poststroke Patients: A Randomized Clinical Trial

Background: Poststroke hemiparesis presents with motor asymmetry and decreased postural control leading to functional limitations. Serious games (SG) for balance rehabilitation of people with stroke may improve motor recovery, and the visual and auditory feedback provided by the SGs helps to explain the therapeutic benefits. However, the contribution of SG combined with kinesthetic and verbal cues during balance training has not been investigated. The aim of this study is to compare the effects of two feedback conditions for an SG balance intervention, with or without the addition of kinesthetic and verbal cues, on balance performance of people with stroke. Methods: Thirty people with chronic poststroke hemiparesis and balance impairment participated in this randomized controlled trial and performed 14 individual SG training sessions combined with kinesthetic and verbal cues provided by the physical therapist or with SG's feedback only. Outcomes were assessed before training (pre), 1 week after the end of training (post), and 8 weeks after the end of training, which were adopted as the follow-up period, using the Balance Evaluation Systems Test, Lower Limb Subscale of Fugl-Meyer, six-minute walk test, and Stroke-Specific Quality of Life Scale. Results: The results showed that SG combined with kinesthetic and verbal cues improved outcomes relating to lower limb function and some balance domains (biomechanical constraints and limits of stability outcomes) better than with SG's feedback only. Both groups had similar significant improvement in quality of life and long-distance walking performance. Conclusion: This study is the first to directly compare two feedback conditions for SG-based balance intervention. The addition of kinesthetic and verbal cues during the SG balance improved aspects of postural control better than without this form of feedback.

Using a Webcam to Assess Upper Extremity Proprioception: Experimental Validation and Application to Persons Post Stroke

Many medical conditions impair proprioception but there are few easy-to-deploy technologies for assessing proprioceptive deficits. Here, we developed a method-called "OpenPoint"-to quantify upper extremity (UE) proprioception using only a webcam as the sensor. OpenPoint automates a classic neurological test: the ability of a person to use one hand to point to a finger on their other hand with vision obscured. Proprioception ability is quantified with pointing error in the frontal plane measured by a deep-learning-based, computer vision library (MediaPipe). In a first experiment with 40 unimpaired adults, pointing error significantly increased when we replaced the target hand with a fake hand, verifying that this task depends on the availability of proprioceptive information from the target hand, and that we can reliably detect this dependence with computer vision. In a second experiment, we quantified UE proprioceptive ability in 16 post-stroke participants. Individuals post stroke exhibited increased pointing error (p < 0.001) that was correlated with finger proprioceptive error measured with an independent, robotic assessment (r = 0.62, p = 0.02). These results validate a novel method to assess UE proprioception ability using affordable computer technology, which provides a potential means to democratize quantitative proprioception testing in clinical and telemedicine environments.

Neuroticism Overestimated? Neuroticism Versus Hypertonia, Pain and Rehabilitation Outcomes in Post-Spinal Cord Injury Patients Rehabilitated Conventionally and with Robotic-Assisted Gait Training

BACKGROUND

The aim of the present study was to analyse the association between neuroticism (one of the Big Five personality traits) and the most common secondary sensorimotor complications occurring in patients after spinal cord injury (SCI), i.e., muscle spasticity (hypertonia) and pain, and to investigate the associations between neuroticism and the effects of conventional rehabilitation (dynamic parapodium) and those using robotic-assisted gait training (RAGT) in this group of patients. In addition, the association of neuroticism with self-efficacy, personal beliefs about pain control, and adopted coping strategies among SCI patients was analysed. These data can be used as a reference for designing effective forms of therapy and support dedicated to this group of patients.

METHODS AND PROCEDURES

Quantitative analysis included 110 patients after SCI. The participants were divided by simple randomisation into a rehabilitation group with RAGT and a rehabilitation group with dynamic parapodium therapy (DPT). The following survey instruments were used for data collection: Revised NEO Personality Inventory (NEO-PI-R); Ashworth Scale; the Spinal Cord Independence Measure III (SCIM III); the Walking Index for Spinal Cord Injury II (WISCI-II); the American Spinal Injury Association Impairment Scale (AIS); the Pain Coping Strategies Questionnaire-CSQ; and the Beliefs about Pain Control Questionnaire-BPCQ.

OUTCOMES AND RESULTS

analyses showed a positive association between neuroticism and spastic tension (rho = 0.39; p < 0.001).

CONCLUSIONS AND IMPLICATIONS

the study showed that a high level of neuroticism correlates with a higher level of spasticity, but no such correlation was observed for pain. Additionally, the study did not show a significant correlation between neuroticism and rehabilitation outcome depending on the rehabilitation modality (RAGT vs. DPT). The results underline the importance of carrying out a psychological diagnosis of patients to provide therapeutic support in the rehabilitation process.

Effects of dual-message tactile sliding takeover requests on takeover performance in an automated driving system

OBJECTIVE

The present study aimed to explore the effects of various tactile takeover requests (TORs) (i.e., tactile sliding TOR and traditional vibration TOR) on the takeover performance in an automated driving system.

METHODS

A tactile sliding motor device was developed to signal the sliding TOR on the seatback of a driving simulator. Twenty-five young drivers were recruited as participants. Four types of TOR patterns were adopted in the study: ipsilateral motor rotation (IR), contralateral motor rotation (CR), ipsilateral and contralateral motor rotation (ICR), and ipsilateral motor vibration (IV). The participants were required to sit on the seat and underwent the automated driving in a low- or high-complexity scenario, then one of the four types of TORs was triggered randomly. The participants were asked to make a lane change using the steering wheel as soon as possible. Objective measures and subjective evaluations were used to assess the takeover performance.

RESULTS

Results showed that the participants exhibited a shorter steering response time and lane change time under the three tactile sliding TORs (compared to the traditional vibration TOR). In the high-complexity scenarios and low-complexity scenarios conditions, different result patterns appeared regarding the maximum lateral acceleration and situational awareness.

CONCLUSION

Our findings suggested that the tactile sliding motor is a promising way to signal a TOR in an automated driving system.

Sensing expectation enables simultaneous proprioception and contact detection in an intelligent soft continuum robot

A high-level perceptual model found in the human brain is essential to guide robotic control when facing perception-intensive interactive tasks. Soft robots with inherent softness may benefit from such mechanisms when interacting with their surroundings. Here, we propose an expected-actual perception-action loop and demonstrate the model on a sensorized soft continuum robot. By sensing and matching expected and actual shape (1.4% estimation error on average), at each perception loop, our robot system rapidly (detection within 0.4 s) and robustly detects contact and distinguishes deformation sources, whether external and internal actions are applied separately or simultaneously. We also show that our soft arm can accurately perceive contact direction in both static and dynamic configurations (error below 10°), even in interactive environments without vision. The potential of our method are demonstrated in two experimental scenarios: learning to autonomously navigate by touching the walls, and teaching and repeating desired configurations of position and force through interaction with human operators.

Reliability of online visual and proprioceptive feedback: impact on learning and sensorimotor coding

Multisensory integration is essential for learning and sensorimotor coding, facilitating learners' adaptation to environmental changes. Recent findings confirm that introducing unreliability into visual feedback enhances the use of motor coding, probably because proprioceptive cues are given greater weight. The present study was designed to test this hypothesis and, more generally, to explore the impact of visual versus proprioceptive cue reliability on learning processes. Participants performed a 12-target pointing sequence 100 times with different combinations of visual and proprioceptive feedback: reliable versus unreliable. Retention tests and intermanual transfer tests were administered 24 h later. Results showed that learning and sensorimotor coding were both affected by the different combinations of visual and proprioceptive cue reliability. Fully reliable feedback allowed for the best retention, while fully unreliable feedback resulted in the worst retention. Visual reliability alone mediated the level of visuospatial coding performance in visuospatial transfer, regardless of the level of proprioceptive reliability, and conversely, reliable proprioception combined with unreliable vision provided the optimum sensory environment for motor coding in the motor transfer test. Overall, our study highlighted the essential role of both visual cue reliability and proprioceptive cue reliability -and their interactions- in motor learning and its generalization.

Maintained volitional activation of the muscle alters the cortical processing of proprioceptive afference from the ankle joint

Cortical proprioceptive processing of intermittent, passive movements can be assessed by extracting evoked and induced electroencephalographic (EEG) responses to somatosensory stimuli. Although the existent prior research on somatosensory stimulations, it remains unknown to what extent ongoing volitional muscle activation modulates the proprioceptive cortical processing of passive ankle-joint rotations. Twenty-five healthy volunteers (28.8 ± 7 yr, 14 males) underwent a total of 100 right ankle-joint passive rotations (4° dorsiflexions, 4 ± 0.25 s inter-stimulus interval, 30°/s peak angular velocity) evoked by a movement actuator during passive condition with relaxed ankle and active condition with a constant plantarflexion torque of 5 ± 2.5 Nm. Simultaneously, EEG, electromyographic (EMG) and kinematic signals were collected. Spatiotemporal features of evoked and induced EEG responses to the stimuli were extracted to estimate the modulation of the cortical proprioceptive processing between the active and passive conditions. Proprioceptive stimuli during the active condition elicited robustly ∼26 % larger evoked response and ∼38 % larger beta suppression amplitudes, but ∼42 % weaker beta rebound amplitude over the primary sensorimotor cortex than the passive condition, with no differences in terms of response latencies. These findings indicate that the active volitional motor task during naturalistic proprioceptive stimulation of the ankle joint enhances related cortical activation and reduces related cortical inhibition with respect to the passive condition. Possible factors explaining these results include mechanisms occurring at several levels of the proprioceptive processing from the peripheral muscle (i.e. mechanical, muscle spindle status, etc.) to the different central (i.e. spinal, sub-cortical and cortical) levels.

"Investigating the combined effects of scapular-focused training and Mulligan mobilization on shoulder impingement syndrome" a three-arm pilot randomized controlled trial

OBJECTIVES

To assess whether the combination of scapular-focused training and mulligan mobilization (SFTMM) improves pain and proprioception compared to scapular-focused training (SFT) and a control group in female rock climbers with shoulder impingement syndrome (SIS).

DESIGN

Three-arm randomized controlled trial (RCT).

SETTING

Outpatient setting.

SUBJECTS

Individuals were randomly assigned to SFTMM, SFT alone, and control group.

INTERVENTIONS

8 weeks of SFTMM and SFT.

MAIN MEASURES

Outcome measures were pain and proprioception.

RESULTS

The results revealed significant differences in pain scores and proprioception among female rock climbers with SIS who participated in SFTMM, SFT, and a control group (F(2, 32) = 81.01, p = 0.001, η2 = 0.83 for pain scores; F(2, 32) = 178.2, p = 0.001, η2 = 0.91 for proprioception scores). Post-hoc tests via the Bonferroni test indicated that both SFTMM and SFT significantly reduced pain levels (p = 0.001) and improved proprioception levels (p = 0.001) compared with the control group. There was no significant difference in pain scores and proprioception between the SFTMM group and the SFT group (p > 0.05).

CONCLUSIONS

In conclusion, the study indicates that SFTMM significantly reduces pain and improves proprioception in female rock climbers with SIS, as shown by notable changes compared to the control group. However, no statistically significant difference was found between the SFTMM (combined intervention) and SFT alone. Therefore, while the incorporation of SFT and MM shows promise; further research is needed to fully understand its long-term benefits and clinical implications.

ETHICAL CODE REGISTRATION

The study was approved at Ethics.

RESEARCH

ac.ir, code: IR.SSRC.REC.1402.170 on 2023-10-22.

The evolution of muscle spindles

Muscle spindles are stretch-sensitive mechanoreceptors found in the skeletal muscles of most four-limbed vertebrates. They are unique amongst sensory receptors in the ability to regulate their sensitivity by contraction of the intrafusal muscle fibres on which the sensory endings lie. Muscle spindles have revealed a remarkable diversity of functions, including reflex action in posture and locomotion, contributing to bodily self awareness, and influencing wound healing. What were the circumstances which gave rise to the evolution of such complex end-organs? We argue that spindles first appeared in early amniotes and only later in frogs and toads. This was considered an example of convergent evolution. Spindles in amphibians and reptiles are characterised by their simple structure, pointing to key features essential for spindle function. Spindle sensitivity in amphibians and reptiles is controlled by intrafusal fibre contractions evoked by branches of motor axons supplying extrafusal muscle. Modern phylogenetic evidence has revised our views on the origin of birds, placing them closer to the dinosaurs than had previously been thought. Birds are the only group, other than mammals, which has a dedicated fusimotor innervation of spindles, another example of convergent evolution, given the widely different origins of the two groups. One factor that may have played a role here was that both groups are endotherms, allowing motor control to develop further in an optimal internal environment. This, as well as other changes within the spindle, has led to the astonishing sophistication of motor control observed especially in many modern mammals.

Smartphone Proprioception for Ankle Navigation (SPAN): Reliability and Effect of Position Exposure Time

This study investigated ankle discriminative acuity and performance and measurement consistency for tests undertaken with different joint position exposure times (PETs). Twenty-four participants were tested using a novel Smartphone Proprioception for Ankle Navigation (SPAN) under four PETs, i.e., 0.25s, 0.5s, 0.75s and 1s, delivered in a random sequence, and then re-tested within one week. The results indicated a PET main effect (F = 10.12, p = 0.004, partial ƞ2 = 0.14), and limb preference main effect (F = 5.39, p = 0.03, partial ƞ2 = 0.19), without significant interactions (p > 0.05). Ankle proprioception improved with prolonged PET, with the non-dominant side outperforming the dominant side. A PET of 0.25s showed good to excellent reliability, with intraclass correlation coefficients (ICCs) of 0.897 (95%CI: 0.761, 0.955) and 0.885 (95%CI: 0.736, 0.951), with standard errors of measurements (SEM) between 0.030 and 0.035, and minimum detectable change at 90% (MDC90) between 0.070 and 0.082, compared to poor to moderate reliability at the other three longer PETs (ICCs =0.352-0.736). The findings suggested the prolongation of PET can improve ankle proprioceptive performance but can amplify the inter-occasion variability, likely due to increased cognitive analysis with longer stimulus sampling. SPAN may thus be a cost-effective and accessible apparatus for clinical practice.

The Unchanging Latency of Transcranial Motor-Evoked Potentials Among Various Age Groups

Background Human growth and development involve significant changes in bodily dimensions, yet motor learning appears to remain stable throughout life. This study investigates whether adjustments in motor velocity take place as individuals age by examining the latency of transcranial motor-evoked potentials (TcMEPs) across different age groups. Methods Data were collected from 100 patients who underwent surgery with intraoperative neuromonitoring at the All India Institute of Medical Sciences, New Delhi, between January 1, 2019, and January 1, 2020. TcMEP recordings were analyzed for 7 commonly monitored muscles across 7 distinct age groups: under 10 years, 10-19 years, 20-29 years, 30-39 years, 40-49 years, 50-59 years, and over 60 years. Results The analysis revealed no significant differences in motor-evoked potential (MEP) latency across the age groups, indicating that motor response latency remains stable despite the physical changes that occur with aging. Conclusion These findings enhance our understanding of motor learning, suggesting that motor response latency does not necessitate changes with age, highlighting the consistency of motor function over the human lifespan.

Bayesian inference in arm posture perception

To configure our limbs in space, the brain must compute their position based on sensory information provided by mechanoreceptors in the skin, muscles, and joints. Because this information is corrupted by noise, the brain is thought to process it probabilistically and integrate it with prior belief about arm posture, following Bayes' rule. Here, we combined computational modeling with behavioral experimentation to test this hypothesis. The model conceives the perception of arm posture as the combination of a probabilistic kinematic chain composed by the shoulder, elbow, and wrist angles, compromised with additive Gaussian noise, with a Gaussian prior about these joint angles. We tested whether the model explains errors in a virtual reality (VR)-based posture matching task better than a model that assumes a uniform prior. Human participants (N = 20) were required to align their unseen right arm to a target posture, presented as a visual configuration of the arm in the horizontal plane. Results show idiosyncratic biases in how participants matched their unseen arm to the target posture. We used maximum likelihood estimation to fit the Bayesian model to these observations and estimate key parameters including the prior means and its variance-covariance structure. The Bayesian model including a Gaussian prior explained the response biases and variance much better than a model with a uniform prior. The prior varied across participants, consistent with the idiosyncrasies in arm posture perception and in alignment with previous behavioral research. Our work clarifies the biases in arm posture perception within a new perspective on the nature of proprioceptive computations.NEW & NOTEWORTHY We modeled the perception of arm posture as a Bayesian computation. A VR posture-matching task was used to empirically test this Bayesian model. The Bayesian model including a nonuniform postural prior well explained individual participants' biases in arm posture matching.

Experimentally induced pain increases absolute but not relative errors and reduces variability in joint repositioning of the knee joint in healthy participants

BACKGROUND

Joint position sense (JPS) plays an important role in knee joint function. Despite the possible influence of pain on the proprioceptive system, the effects of experimental muscle pain on knee JPS have not been studied.

OBJECTIVES

To investigate if experimentally induced muscle pain affects knee JPS in healthy participants.

METHODS

Measurements of knee JPS were conducted before and after the injection of 5.8% sterile hypertonic saline in the vastus medialis muscle of 26 healthy physically active adults. Knee JPS was assessed through a passive/active repositioning paradigm in target angles of 15°, 45° and 60° using an isokinetic dynamometer. Absolute and relative angular errors were calculated. The coefficient of variation analysis was used to assess differences in the angles' variability during the repositioning task.

RESULTS

Absolute angular error increased in all three angles following experimentally induced pain. The difference was statistically significant at 45° (p = 0.003, d = 0.6) and 15° (p = 0.047, d = 0.4) but not at 60° (p = 0.064, d = 0.4). Relative error did not show directional bias at 45° (p = 0.272, d = 0.2), 15° (p = 0.483, d = 0.1) or 60° (p = 0.091, d = 0.3). The coefficient of variation analysis revealed a statistically significant reduction in variability at angles of 60° (p = 0.002, d = 0.7) and 15° (p = 0.031, d = 0.4) after the pain intervention.

CONCLUSION

The presence of experimentally induced muscle pain affects the ability of healthy participants to accurately reposition the knee at two angles of knee flexion and reduces movement variability during the repositioning task. Further research is required to determine if these deficits also impact patients with clinical knee pain.

Lack of visual experience leads to severe distortions in the hand representation of the body model

This study investigates the impact of vision on the maintenance of hand representation in the implicit body model, particularly focusing on congenitally blind individuals. To address this, we performed a hand landmark localization task on blind individuals who lacked visual experience of their bodies and compared their performance to normally sighted and normally sighted but blindfolded participants. Through measurements of finger lengths, hand width, and shape index, we demonstrate that blind participants exhibit significantly greater distortions in their hand representation compared to sighted and blindfolded controls. Notably, blind individuals displayed a marked overestimation of hand width and an underestimation of finger lengths, particularly in digits D2, D3, and D4. Surprisingly, blind subjects with partial vision displayed more severe distortions than those with no residual vision. Furthermore, our findings reveal that late-blind participants exhibit similar levels of distortion as congenitally blind individuals, suggesting an extended period of susceptibility to the lack of visual input in shaping body representations. The Reverse Distortion (RD) hypothesis provides a plausible explanation for these distortions, suggesting that compensatory mechanisms occur within the body model to counteract the anisotropic cortical representations. Our results support this hypothesis: blind individuals have expanded cortical representations processing tactile information, so this could lead to more pronounced distortions in their hand representation of the body model. This underscores the importance of visual input in modulating body representations. Overall, our study highlights the malleability of body representations and the intricate interplay between sensory inputs and cortical processing in shaping the implicit body model.

Age-Related Changes in Postural Stability in Response to Varying Surface Instability in Young and Middle-Aged Adults

As individuals transition into middle age, subtle declines in postural control may occur due to gradual reductions in neuromuscular control. The current study aimed to examine the effect of age on bipedal postural control across three support surfaces with varying degrees of instability: a firm surface, a foam pad, and a multiaxial balance board. The effect of surface stability was also assessed. Postural accelerations were recorded using a tri-axial accelerometer placed over the lumbar spine (L5) in 24 young female adults (23.9 ± 5.3 years) and 24 middle-aged female adults (51.4 ± 5.9 years). Sample entropy (SampEn) was used to analyze the complexity of postural control by measuring the regularity of postural acceleration. The main results show significant age-related differences in the mediolateral and anteroposterior acceleration directions (p ≤ 0.012). Young adults exhibit more irregular fluctuations in postural acceleration (high SampEn), reflecting greater efficiency or automaticity in postural control compared to middle-aged adults. Increased surface instability also progressively decreases SampEn in the mediolateral direction (p < 0.001), reflecting less automaticity with increased instability. However, no interaction effects are observed. These findings imply that incorporating balance training on unstable surfaces might help middle-aged adults maintain postural control and prevent future falls.

Joint position and force senses in young female tennis players and untrained adolescents

The aim of the study was to determine the differences between tennis players and untrained peers in the development of upper limb proprioception in 10-15-year-olds. A group of 67 girls (12.75 ± 1.46 years old), including 33 tennis players and 34 age-matched untrained controls, was divided into three age groups: A1, 10-11-years-old; A2, 12-13-years-old; and A3, 14-15-years-old. Joint position sense (JPS) and force sense (FS) were assessed by reproducing memorized target angle or torque value of three joints: glenohumeral, elbow, and radiocarpal. The JPS error for the elbow joint in group A1 was 71% and 80% higher (p < 0.01) than that in groups A2 and A3, respectively, and the performance of all tennis players was 27.5% (p = 0.01) better than that of untrained controls. For FS, proprioception of only the more demanding task tested (reproduction of 50% maximal voluntary contraction) and specific function (elbow and radiocarpal extension, and glenohumeral internal rotation) showed development with age. The error values for elbow extension (A1, A2) and the glenohumeral joint (A3) of tennis players were lower than those of age-matched controls. We conclude that the development of FS in the upper limb varied and was related to the specific functions and joints. The 10-13-year-old tennis players showed elbow extensor FS performance at the level of the older participants, while the 14-15-year-old tennis players were characterized with superior FS internal rotation performance in the glenohumeral joint.

Exploring mechanisms of anhedonia in depression through neuroimaging and data-driven approaches

BACKGROUND

Anhedonia is a core symptom of depression that is closely related to prognosis and treatment outcomes. However, accurate and efficient treatments for anhedonia are lacking, mandating a deeper understanding of the underlying mechanisms.

METHODS

A total of 303 patients diagnosed with depression and anhedonia were assessed by the Snaith-Hamilton Pleasure Scale (SHAPS) and magnetic resonance imaging (MRI). The patients were categorized into a low-anhedonia group and a high-anhedonia group using the K-means algorithm. A data-driven approach was used to explore the differences in brain structure and function with different degrees of anhedonia based on MATLAB. A random forest model was used exploratorily to test the predictive ability of differences in brain structure and function on anhedonia in depression.

RESULTS

Structural and functional differences were apparent in several brain regions of patients with depression and high-level anhedonia, including in the temporal lobe, paracingulate gyrus, superior frontal gyrus, inferior occipital gyrus, right insular gyrus, and superior parietal lobule. And changes in these brain regions were significantly correlated with scores of SHAPS.

CONCLUSIONS

These brain regions may be useful as biomarkers that provide a more objective assessment of anhedonia in depression, laying the foundation for precision medicine in this treatment-resistant, relatively poor prognosis group.

Clinical Applications and Future Translation of Somatosensory Neuroprostheses

Somatosensory neuroprostheses restore, replace, or enhance tactile and proprioceptive feedback for people with sensory impairments due to neurological disorders or injury. Somatosensory neuroprostheses typically couple sensor inputs from a wearable device, prosthesis, robotic device, or virtual reality system with electrical stimulation applied to the somatosensory nervous system via noninvasive or implanted interfaces. While prior research has mainly focused on technology development and proof-of-concept studies, recent acceleration of clinical studies in this area demonstrates the translational potential of somatosensory neuroprosthetic systems. In this review, we provide an overview of neurostimulation approaches currently undergoing human testing and summarize recent clinical findings on the perceptual, functional, and psychological impact of somatosensory neuroprostheses. We also cover current work toward the development of advanced stimulation paradigms to produce more natural and informative sensory feedback. Finally, we provide our perspective on the remaining challenges that need to be addressed prior to translation of somatosensory neuroprostheses.

The effect of juggling on the proprioceptive and attentional abilities among older women

Background

Age-related changes in attentional abilities can lead to a decline in body segment awareness in space. However, studies have reported that physical activity can improve proprioception among older adults, although proven activities with this potential are limited. Juggling is a promising activity for enhancing proprioception, as it requires high levels of attention and sensory precision. The first hypothesis posited that a juggling intervention would positively impact ipsilateral and contralateral elbow joint position matching without visual input. The second hypothesis suggested a correlation between cognitive abilities and joint position sense efficiency.

Methods

A total of 20 older women (mean age: 69.95 ± 4.58) participated in a repeated-measures study using a Latin square design. Measurements were taken at three time points (baseline, post-juggling, and control). Ipsilateral and contralateral elbow joint position matchings without visual or verbal feedback of accuracy were used to assess proprioception. Attention and reaction time variables were measured using the Vienna Test System protocols.

Results

Although significant changes were observed between baseline and subsequent time points in joint position sense accuracy, no specific effect of juggling was detected. Low and medium correlations were found between decision time and the variability of choice reaction time with contralateral accuracy. For ipsilateral accuracy, a relationship was observed only with handedness. No correlations were found between attention test scores and joint position sense accuracy.

Conclusion

The study did not demonstrate a significant effect of juggling on position-matching ability. However, cognitive abilities such as decision speed and the stability of choice reaction time may play a role in enhancing position-matching in older women.

Clinical trial registration

ClinicalTrials.gov, identifier NCT06108713.

The Correlation Between Cervical Proprioception and Scapular Dyskinesis in Patients With Neck Pain: A Case-Control Study

Introduction Neck pain is common among office workers, and the assessment of cervical proprioception and scapular dyskinesis is key in the management of patients with neck pain. While some studies have shown the relevance of both factors in neck pain patients, the correlation between the two parameters has not yet been investigated. Hence, this study aimed to determine the correlation between cervical proprioception and scapular dyskinesis in workplace computer users without neck pain (control group) versus those with neck pain (case group). Methodology A case-control, correlational study was performed within office settings; based on the selection criteria, 88 participants were included and categorized into two groups consisting of 44 workplace computer users without neck pain in the control group (Group A) and 44 workplace computer users with neck pain in the case group (Group B). Cervical proprioception was evaluated by using the joint position error (JPE) test and scapular dyskinesis was assessed using the modified lateral scapular slide test (MLSST). Results There was a statistically significant difference in cervical proprioception and scapular dyskinesis between the case and control groups (p<0.001). Workplace computer users with neck pain showed greater JPE compared to those without neck pain, and scapular dyskinesis was observed in the case group. Moreover, Spearman's correlation coefficient showed a significant correlation between cervical proprioception and scapular dyskinesis in workplace computer users with neck pain. Conclusions The present study provides guidance on the assessment as well as management of JPE with different positions of scapular dyskinesia. The evaluation of scapular dyskinesis is frequent clinically; given its positive correlation, managing JPE in neck pain patients is feasible.

Effectiveness of a home training program on improving pinch force perception in older adults

BACKGROUND

Hand function is reduced with aging which can lead to impairments in the performance of daily activities and eventually loss of independence. The ability to perceive the forces being applied to an object is an important component of hand control that also declines with age. However, the extent to which force perception can be improved through training remains largely unknown.

PURPOSE

This study evaluated the effectiveness of a home-training program focused on improving force perception in older adults.

STUDY DESIGN

Quasi-experimental - Uncontrolled trial.

METHODS

Eleven independent, healthy adults (mean age: 77.2 ± 6.8 years) participated in a home-based sensorimotor hand training program 6 days/week for 6 weeks. Force perception, the primary outcome variable, was measured as the ability to reproduce a pinch force equal to 25% maximum voluntary contraction in the absence of visual feedback using either the ipsilateral remembered or contralateral concurrent (CC) hand. We also measured hand strength, dexterity, tactile acuity, and cognition before and after training.

RESULTS

After the program was completed, participants showed a 35% reduction in absolute (p < 0.01, confidence interval (CI): [7.3, 33.2], effect sizes (ES): 0.87) and constant (p = 0.05, CI: [0.0, 34.9], ES: 0.79) force matching errors in the CC condition. Improvements in dominant hand dexterity (Purdue pegboard test) (p < 0.05, CI: [0.2, 2.4], ES: 0.60) and tactile sensitivity (JVP thresholds) (p < 0.05, CI: [-1.7, -0.1], ES: 0.94), as well as cognition (Trail Making Test B) (p < 0.05, CI: [-24,1. -1.6], ES: 0.30) were also observed post-training.

CONCLUSIONS

The results suggest that home-hand training can be an effective way to improve force perception among older adults.

Local muscle pressure stimulates the principal receptors for proprioception

Proprioception plays a crucial role in motor coordination and self-perception. Muscle spindles are the principal receptors for proprioception. They are believed to encode muscle stretch and signal limb position and velocity. Here, we applied percutaneous pressure to a small area of extensor muscles at the forearm while recording spindle afferent responses, skeletal muscle activity, and hand kinematics. Three levels of sustained pressure were applied on the spindle-bearing muscle when the hand was relaxed and immobile ("isometric" condition) and when the participant's hand moved rhythmically at the wrist. As hypothesized to occur due to compression of the spindle capsule, we show that muscle pressure is an "adequate" stimulus for human spindles in isometric conditions and that pressure enhances spindle responses during stretch. Interestingly, release of sustained pressure in isometric conditions lowered spindle firing below baseline rates. Our findings urge a re-evaluation of muscle proprioception in sensorimotor function and various neuromuscular pathologies.

Sway detection in hypertension as a novel tool to anticipate risk and morbidity due to postural instability

Objectives:

Hypertension contributes substantially to poor physical function and autonomic imbalance. It may cause instability in posture that limits daily activities and can lead to devastating falls. Centre of pressure (CoP) is a commonly used index of postural stability while standing and is a measure of the activity of the motor system, which may be altered in hypertension. It is also observed that the fall incidence is higher in women than men, which may be due to postural instability. The pilot study was conducted to see whether the presence of essential hypertension further contributes to postural instability in women and compared with age-matched normotensive controls.

Materials and Methods:

Sixteen hypertensive women on regular treatment for hypertension and 16 age-matched normotensive women with a mean age of 51.9 ± 9.1 years were included in the study. The WII balance board was used to measure the CoP and displacement to sway. PowerLab 8/35 (AD instruments) with LabChart software was used to measure the parameters.

Results:

Displacement of CoP in the mediolateral direction was studied in the trials. The CoP was measured in eyes closed and eyes open conditions and was displaced in both groups, with significant displacement in hypertensive women. With voluntary sway to their right and left sides, hypertensive women have shown significantly less sway displacement compared to normotensive women. In hypertensives, during right sway, the error of correction was 13%. During left sway, overcorrection was high in both hypertensive and normotensive.

Conclusion:

Postural instability is observed in hypertension, and posturography can be used as a routine screening tool to predict postural instability in hypertensives. Balance training exercise biofeedback protocols and the use of sensory augmentation devices may prove to be useful in improving postural stability.

The Discrepancy Between External and Internal Load/Intensity during Blood Flow Restriction Exercise: Understanding Blood Flow Restriction Pressure as Modulating Factor

Physical exercise induces acute psychophysiological responses leading to chronic adaptations when the exercise stimulus is applied repeatedly, at sufficient time periods, and with appropriate magnitude. To maximize long-term training adaptations, it is crucial to control and manipulate the external load and the resulting psychophysiological strain. Therefore, scientists have developed a theoretical framework that distinguishes between the physical work performed during exercise (i.e., external load/intensity) and indicators of the body's psychophysiological response (i.e., internal load/intensity). However, the application of blood flow restriction (BFR) during exercise with low external loads/intensities (e.g., ≤ 30% of the one-repetition-maximum, ≤ 50% of maximum oxygen uptake) can induce physiological and perceptual responses, which are commonly associated with high external loads/intensities. This current opinion aimed to emphasize the mismatch between external and internal load/intensity when BFR is applied during exercise. In this regard, there is evidence that BFR can be used to manipulate both external load/intensity (by reducing total work when exercise is performed to exhaustion) and internal load/intensity (by leading to higher physiological and perceptual responses compared to exercise performed with the same external load/intensity without BFR). Furthermore, it is proposed to consider BFR as an additional exercise determinant, given that the amount of BFR pressure can determine not only the internal but also external load/intensity. Finally, terminological recommendations for the use of the proposed terms in the scientific context and for practitioners are given, which should be considered when designing, reporting, discussing, and presenting BFR studies, exercise, and/or training programs.

The functional role of conscious sensation of movement

This paper proposes a new framework for investigating neural signals sufficient for a conscious sensation of movement and their role in motor control. We focus on signals sufficient for proprioceptive awareness, particularly from muscle spindle activation and from primary motor cortex (M1). Our review of muscle vibration studies reveals that afferent signals alone can induce conscious sensations of movement. Similarly, studies employing peripheral nerve blocks suggest that efferent signals from M1 are sufficient for sensations of movement. On this basis, we show that competing theories of motor control assign different roles to sensation of movement. According to motor command theories, sensation of movement corresponds to an estimation of the current state based on afferent signals, efferent signals, and predictions. In contrast, within active inference architectures, sensations correspond to proprioceptive predictions driven by efferent signals from M1. The focus on sensation of movement provides a way to critically compare and evaluate the two theories. Our analysis offers new insights into the functional roles of movement sensations in motor control and consciousness.

Reduction in preparatory brain activity preceding gait initiation in individuals with chronic ankle instability: A movement-related cortical potential study

Evidence suggests that chronic ankle instability (CAI) is not merely a peripheral musculoskeletal injury but should be recognized as a neurophysiological dysfunction. This reflects a paradigm shift from focusing on peripheral structural changes to emphasizing the central nervous system. However, changes in cortical activity during functional activities remain poorly understood. Thus, this study aimed to compare preparatory brain activity during gait initiation (GI) through movement-related cortical potentials (MRCPs) in individuals with CAI and healthy subjects. The proactive components of MRCPs, including contingent negative variation (CNV) and event-related desynchronization (ERD), were measured using electroencephalography. The primary outcomes were late CNV amplitude, CNV peak amplitude, CNV peak time, and alpha/beta ERD. The results indicated that the late CNV amplitude was significantly lower in the CAI group compared to the healthy group at the Fz and Cz electrodes (P < 0.001). The CAI group also demonstrated lower CNV peak amplitude at the Fz, Cz, and Pz electrodes (P < 0.0025). Additionally, in the CAI group, signals peaked earlier at the Cz electrode (P = 0.002). Furthermore, alpha ERD at Pz was significantly lower in the CAI group than in the healthy group (P = 0.003), suggesting diminished preparatory brain activity during GI in CAI subjects. Recognizing CAI as a condition involving both peripheral and central dysfunctions highlights the importance of a multidisciplinary approach in treatment and rehabilitation. This approach should target brain activity in addition to peripheral structures, potentially leading to improved long-term outcomes for patients.

Minimal impact of chronic proprioceptive loss on implicit sensorimotor adaptation and perceived movement outcome

Implicit sensorimotor adaptation keeps our movements well calibrated amid changes in the body and environment. We have recently postulated that implicit adaptation is driven by a perceptual error: the difference between the desired and perceived movement outcome. According to this perceptual realignment model, implicit adaptation ceases when the perceived movement outcome-a multimodal percept determined by a prior belief conveying the intended action, the motor command, and feedback from proprioception and vision-is aligned with the desired movement outcome. Here, we examined the role of proprioception in implicit motor adaptation and perceived movement outcome by examining individuals who experience deafferentation (i.e., individuals with impaired proprioception and touch). We used a modified visuomotor rotation task designed to isolate implicit adaptation and probe perceived movement outcomes throughout the experiment. Surprisingly, both implicit adaptation and perceived movement outcome were minimally impacted by chronic deafferentation, posing a challenge to the perceptual realignment model of implicit adaptation.NEW & NOTEWORTHY We tested six individuals with chronic somatosensory deafferentation on a novel task that isolates implicit sensorimotor adaptation and probes perceived movement outcome. Strikingly, both implicit motor adaptation and perceptual movement outcome were not significantly impacted by chronic deafferentation, posing a challenge for theoretical models of adaptation that involve proprioception.

Reliability of cervicocephalic sense of force

Cervicocephalic proprioception (CCP) is an important assessment item for people with a range of clinical conditions, where reduced CCP is associated with neck pain and imbalance. Reliability has been established for a range of positional and movements tests, but there is limited data regarding sense of force, particularly across three planes of movement. The current test-retest study assessed reliability when evaluating sense of force in healthy adults (8 males, 6 females, mean age 31.50 years [SD 10.14]) over two sessions, 4-7 days apart. A force matching protocol was used to evaluate reliability of absolute error (AE), constant error (CE), and variable error (VE) for 10 % and 25 % maximal voluntary contraction (MVC) target forces for flexion, extension, lateral flexion, and rotation. Participants were strapped to a chair to limit trunk movement and data was captured using a compressive force transducer fixed to an adjustable wall mount. Six trials were performed for each contraction-type, totaling 72 submaximal MVCs per session. ICC estimates for AE (0.15-0.77), CE (0.01-0.85), and VE (0.00-0.83) were varied and confidence intervals were mostly wide. Considering lower limits of confidence intervals, CE had best reliability values generally, but more specifically the most reliable contraction type and movement was 25 % MVC flexion (ICC 0.85, confidence interval 0.54-0.95). This study found that reliability for sense of force testing was dependent upon contraction, type of error, and target force utilized. Further reliability analysis should be performed when applying this test to measure validity outcomes in clinical populations.

Differential encoding of mammalian proprioception by voltage-gated sodium channels

Animals that require purposeful movement for survival are endowed with mechanosensory neurons called proprioceptors that provide essential sensory feedback from muscles and joints to spinal cord circuits, which modulates motor output. Despite the essential nature of proprioceptive signaling in daily life, the mechanisms governing proprioceptor activity are poorly understood. Here, we have identified distinct and nonredundant roles for two voltage-gated sodium channels (NaVs), NaV1.1 and NaV1.6, in mammalian proprioception. Deletion of NaV1.6 in somatosensory neurons (NaV1.6cKO mice) causes severe motor deficits accompanied by complete loss of proprioceptive transmission, which contrasts with our previous findings using similar mouse models to target NaV1.1 (NaV1.1cKO). In NaV1.6cKO animals, loss of proprioceptive feedback caused non-cell-autonomous impairments in proprioceptor end-organs and skeletal muscle that were absent in NaV1.1cKO mice. We attribute the differential contribution of NaV1.1 and NaV1.6 in proprioceptor function to distinct cellular localization patterns. Collectively, these data provide the first evidence that NaV subtypes uniquely shape neurotransmission within a somatosensory modality.

Crossmodal sensory neurons based on high-performance flexible memristors for human-machine in-sensor computing system

Constructing crossmodal in-sensor processing system based on high-performance flexible devices is of great significance for the development of wearable human-machine interfaces. A bio-inspired crossmodal in-sensor computing system can perform real-time energy-efficient processing of multimodal signals, alleviating data conversion and transmission between different modules in conventional chips. Here, we report a bio-inspired crossmodal spiking sensory neuron (CSSN) based on a flexible VO2 memristor, and demonstrate a crossmodal in-sensor encoding and computing system for wearable human-machine interfaces. We demonstrate excellent performance in the VO2 memristor including endurance (>1012), uniformity (0.72% for cycle-to-cycle variations and 3.73% for device-to-device variations), speed (<30 ns), and flexibility (bendable to a curvature radius of 1 mm). A flexible hardware processing system is implemented based on the CSSN, which can directly perceive and encode pressure and temperature bimodal information into spikes, and then enables the real-time haptic-feedback for human-machine interaction. We successfully construct a crossmodal in-sensor spiking reservoir computing system via the CSSNs, which can achieve dynamic objects identification with a high accuracy of 98.1% and real-time signal feedback. This work provides a feasible approach for constructing flexible bio-inspired crossmodal in-sensor computing systems for wearable human-machine interfaces.

A computational study of how an α- to γ-motoneurone collateral can mitigate velocity-dependent stretch reflexes during voluntary movement

The primary motor cortex does not uniquely or directly produce alpha motoneurone (α-MN) drive to muscles during voluntary movement. Rather, α-MN drive emerges from the synthesis and competition among excitatory and inhibitory inputs from multiple descending tracts, spinal interneurons, sensory inputs, and proprioceptive afferents. One such fundamental input is velocity-dependent stretch reflexes in lengthening muscles, which should be inhibited to enable voluntary movement. It remains an open question, however, the extent to which unmodulated stretch reflexes disrupt voluntary movement, and whether and how they are inhibited in limbs with numerous multiarticular muscles. We used a computational model of a Rhesus Macaque arm to simulate movements with feedforward α-MN commands only, and with added velocity-dependent stretch reflex feedback. We found that velocity-dependent stretch reflex caused movement-specific, typically large and variable disruptions to arm movements. These disruptions were greatly reduced when modulating velocity-dependent stretch reflex feedback (i) as per the commonly proposed (but yet to be clarified) idealized alpha-gamma (α-γ) coactivation or (ii) an alternative α-MN collateral projection to homonymous γ-MNs. We conclude that such α-MN collaterals are a physiologically tenable propriospinal circuit in the mammalian fusimotor system. These collaterals could still collaborate with α-γ coactivation, and the few skeletofusimotor fibers (β-MNs) in mammals, to create a flexible fusimotor ecosystem to enable voluntary movement. By locally and automatically regulating the highly nonlinear neuro-musculo-skeletal mechanics of the limb, these collaterals could be a critical low-level enabler of learning, adaptation, and performance via higher-level brainstem, cerebellar, and cortical mechanisms.