The contribution of motor commands to position sense differs between elbow and wrist

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.

Comparison of the validity and reliability of three different methods used for wrist proprioception measurement

BACKGROUND

ː Early detection of loss of proprioception is essential to prevent injury and maintain professional work activities. However, although many different methods are present for wrist proprioception measurement, these methods' validity and reliability studies are quite limited.

OBJECTIVE

To compare the validity and reliability of the goniometer, inclinometer, and joint position sense goniometer methods used in measuring wrist active joint position sense (AJPS).

METHODS

ː Thirty-two volunteer healthy participants (64 wrists) between the ages of 19-31 (mean age:23,34 ± 3,84) were included in the study. Wrist AJPS was assessed with an isokinetic dynamometer as a reference standard in addition to an inclinometer, goniometer, and joint position sense goniometer (JPSG). Spearman's Correlation Coefficient was used for validity analysis, and Intraclass Correlation Coefficient (ICC3,1) was used to analyze test-retest reliability.

RESULTS

ː It was found that the goniometer (p < 0.001, r = 0.529) is a moderately valid method to assess active wrist joint position sense. The JPSG (p < 0.001, r = 0.432) and inclinometer (p = 0.005, r = 0.350) have weak validity. According to the results of ICC3,1 analysis, the goniometer (p < 0.001, ICC3,1 = 0.422) and JPSG (p < 0.001, ICC3,1 = 0.369) were found to have poor reliability in assessing wrist AJPS, and the inclinometer (p = 0,183, ICC3,1 = 0,114) was not found as a reliable method.

CONCLUSIONS

ː Our results suggest that the JPSG and inclinometer should not be used in the wrist active joint position sense evaluation because of weak validity and poor reliability. The goniometer can be used in clinics and academic research to evaluate wrist joint position sense if the rater lacks a reliable and valid measurement tool.

Elbow Joint Position and Force Senses in Young and Adult Untrained People and Gymnasts

Joint position (JPS) and force senses (FS) are the proprioception modalities. While the development of JPS was investigated both in children/adult and athlete/untrained conditions, there is a lack of insight into the development of FS. Overall, 28 gymnasts and 25 untrained controls underwent proprioception testing. They were divided into two groups: 9 to 11-year-old boys (13 gymnasts and 10 non-athletes) and 18 to 25-year-old adults (15 gymnasts and 15 non-athletes). The testing was performed at an isokinetic dynamometer and included elbow JPS and FS (20% and 50% maximal voluntary contraction) tasks. Children had two times higher error in JPS (p < 0.01) and 50% higher errors in FS of both flexor (p < 0.001) and extensor muscles (p < 0.05) in comparison with adults. Only in the 50% maximal voluntary contraction task, gymnasts showed 33% lower error than the controls (p < 0.01). Untrained boys presented 54%, 132%, and 169% higher error for elbow flexor performance than young gymnasts, untrained adults, and adult gymnasts, respectively (p < 0.01). The 9 to 11-year-old participants were characterized by a lower precision of JPS and FS performance in comparison with adults. Gymnastic training can possibly accelerate the development of FS when higher loads are considered.

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.

The effects of eccentric exercise-induced fatigue on position sense during goal-directed movement

We investigated the impairment of position sense associated with muscle fatigue. In Exp. 1, participants performed learned eccentric extension (22 °/s) movements of the elbow as the arm was pulled through the horizontal plane without vision of the arm. They opened their closed right hand when they judged it to be passing through a target. Dynamic position sense was assessed via accuracy of limb position to the target at time of hand opening. Eccentric movements were performed against a flexion load (10% of flexion MVC). We investigated performance under conditions with and without biceps vibration, as well as before and after eccentric exercise. In Exp. 2, a motor was used to extend the participant's limb passively. We compared conditions with and without vibration of the lengthening but passive biceps, before and after exercise. In Exp. 1, vibration of the active biceps resulted in participants opening their hand earlier ( [95% CI] -5.52° [-7.40, -3.63]) compared to without vibration. Exercise reduced flexion MVCs by ~44%, and participants undershot the target more (-5.51° [-9.31, -1.70]) in the post-exercise block during control trials. Exercise did not influence the persistence of the vibratory illusion. In Exp. 2, vibration resulted in greater undershooting (-2.99° [-3.99, -1.98]) compared to without vibration, before and after exercise. Although exercise reduced MVCs by ~50%, the passive task showed no effects of exercise. We suggest that the CNS continues to rely on muscle spindles for limb position sense, even when they reside in a muscle exposed to fatiguing eccentric contractions.

Secondary endings of muscle spindles: Structure, reflex action, role in motor control and proprioception

NEW FINDINGS

What is the topic of this review? We describe the structure and function of secondary sensory endings of muscle spindles, their reflex action and role in motor control and proprioception. What advances does it highlight? In most mammalian skeletal muscles, secondary endings of spindles are more or much more numerous than primary endings but are much less well studied. By focusing on secondary endings in this review, we aim to redress the balance, draw attention to what is not known and stimulate future research.

ABSTRACT

Kinaesthesia and the control of bodily movement rely heavily on the sensory input from muscle spindles. Hundreds of these sensory structures are embedded in mammalian muscles. Each spindle has one or more sensory endings and its own complement of small muscle fibres that are activated by the CNS via fusimotor neurons, providing efferent control of sensory responses. Exactly how the CNS wields this influence remains the subject of much fascination and debate. There are two types of sensory endings, primary and secondary, with differing development, morphology, distribution and responsiveness. Spindle primary endings have received more attention than secondaries, although the latter usually outnumber them. This review focuses on the secondary endings. Their location within the spindle, their response properties, the projection of their afferents within the CNS and their reflex actions all suggest that secondaries have certain separate roles from the primaries in proprioception and motor control. Specifically, spindle secondaries seem more adapted than primaries to signalling slow and maintained changes in the relative position of bodily segments, thereby contributing to position sense, postural control and static limb positioning. By highlighting, in this way, the roles of secondary endings, a final aim of the review is to broaden understanding of muscle spindles more generally and of the important contributions they make to both sensory and motor mechanisms.

Two senses of human limb position: methods of measurement and roles in proprioception

The sense of position of the body and its limbs is a proprioceptive sense. Proprioceptors are concerned with monitoring the body's own actions. Position sense is important because it is believed to contribute to our self-awareness. This review discusses recent developments in the debate about the sources of peripheral afferent signals contributing to position sense and describes different methods of measurement of position sense under conditions where vision does not participate. These include pointing to or verbal reporting of the perceived position of a hidden body part, alignment of one body part with the perceived position of another, or using memory-based repositioning tasks. The evidence suggests that there are at least two different mechanisms involved in the generation of position sense, mechanisms using different central processing pathways. The principal sensory receptor responsible for position sense is believed to be the muscle spindle. One criterion for identifying mechanism is whether position sense can be manipulated by controlled changes in spindle discharge rates. Position sense measured in two-limb matching is altered in a predictable way by such changes, while values for pointing and verbal reporting remain unresponsive. It is proposed that in two-limb matching the sensation generated is limb position in postural space. In pointing or verbal reporting, information is provided about limb position in extrapersonal space. Here vision is believed to play a role. The evidence suggests that we are aware, at the same time, of sensations of limb position in postural space as well as in extrapersonal space.

Can texture change joint position sense at the knee joint in those with poor joint position accuracy?

Purpose: Skin contributes to joint position sense (JPS) at multiple joints. Altered cutaneous input at the foot can modulate gait and balance and kinesiology tape can enhance proprioception at the knee, but its effect may be dependent on existing capacity. The effect of texture at the knee, particularly in those with poor proprioception, is unknown. The aim of this study was to determine the effect of textured panels on JPS about the knee. Materials and methods: Eighteen healthy females were seated in an adjustable chair. Their left leg (target limb) moved passively from 65° to a target of flexion (115° or 90°) or extension (40°). Their right leg (matching limb) was passively moved towards this target angle and participants indicated when their limbs felt aligned. We tested three textured panels over the knee of the matching limb and two control conditions. The target limb maintained a control panel. Directional error, absolute error and variable error in matching between limbs were calculated. Results: On average textured panels over the knee increased JPS error compared to control pants for participants with poor JPS. These participants undershot the target at 90° of flexion significantly more with textured panels (-11° ± 3°) versus control (-7° ± 3°, p = 0.04). Conclusions: For participants with poor JPS accuracy, increased JPS error at 90° with a textured panel suggests these individuals utilised altered cutaneous information to adjust joint position. We propose increased error results from enhanced skin input at the knee leading to the perception of increased flexion.

Minimal force transmission between human thumb and index finger muscles under passive conditions

It has been hypothesized that force can be transmitted between adjacent muscles. Intermuscle force transmission violates the assumption that muscles act in mechanical isolation, and implies that predictions from biomechanical models are in error due to mechanical interactions between muscles, but the functional relevance of intermuscle force transmission is unclear. To investigate intermuscle force transmission between human flexor pollicis longus and the index finger part of flexor digitorum profundus, we compared finger flexion force produced by passive thumb flexion after one of three conditioning protocols: passive thumb flexion-extension cycling, thumb flexion maximal voluntary contraction (MVC), and thumb extension stretch. Finger flexion force increased after all three conditions. Compared to passive thumb flexion-extension cycling, change in finger flexion force was less after thumb extension stretch (mean difference 0.028 N, 95% CI 0.005 to 0.051 N), but not after thumb flexion MVC (0.007 N, 95% CI -0.020 to 0.033 N). As muscle conditioning changed finger flexion force produced by passive thumb flexion, the change in force is likely due to intermuscle force transmission. Thus, intermuscle force transmission resulting from passive stretch of an adjacent muscle is probably small enough to be ignored.

Effort matching between arms depends on relative limb geometry and personal control

Proprioception encompasses our sense of position and movement of our limbs, as well as the effort with which we engage in voluntary actions. Historically, sense of effort has been linked to centrally generated signals that elicit voluntary movements. We were interested in determining the effect of differences in limb geometry and personal control on sense of effort. In experiment 1, subjects exerted either extension or flexion torques to resist a torque applied by a robot exoskeleton to their reference elbow. They attempted to match this torque by exerting an equal effort torque (in a congruent direction with the reference arm) with their opposite (matching) arm in different limb positions (±15°). Subjects produced greater matching torque when their matching arm exerted effort toward the mirrored position of the reference (e.g., reference/matching arms at 90°/105° elbow flexion) vs. away (e.g., 90°/75° flexion). In experiment 2, a larger angular difference between arms (30°) resulted in a larger discrepancy in matched torques. Furthermore, in both experiments 1 and 2, subjects tended to overestimate the reference arm torque. This motivated a third experiment to determine whether providing more personal control might influence perceived effort and reduce the overestimation of the reference torques that we observed ( experiments 3a and 3b). Overestimation of the matched torques decreased significantly when subjects self-selected the reference torque that they were matching. Collectively, our data suggest that perceived effort between arms can be influenced by signals relating to the relative geometry of the limbs and the personal control of motor output during action. NEW & NOTEWORTHY This work highlights how limb geometry influences our sense of effort during voluntary motor actions. It also suggests that loss of personal control during motor actions leads to an increase in perceived effort.

Kinesthetic Senses

The kinesthetic senses are the senses of position and movement of the body, senses we are aware of only on introspection. A method used to study kinesthesia is muscle vibration, which engages afferents of muscle spindles to trigger illusions of movement and changed position. When vibrating elbow flexors, it generates sensations of forearm extension, when vibrating extensors, sensations of forearm flexion. Vibrating the elbow joint produces no illusion. Vibrating flexors and extensors together at the same frequency also produces no illusion, because what is perceived is the signal difference between antagonist muscles of each arm and between arms. The size of the illusion depends on how the muscle has been conditioned beforehand, due to a property of muscle called thixotropy. When measuring the illusion, blindfolded subjects may carry out a matching or pointing task. In pointing, signals from muscle spindles are less important than in matching. Afferent signals from kinesthetic receptors project to areas of somatosensory cortex to generate sensations of detection and location. This is referred to the body model, which provides information about size and shape of body parts. Kinesthesia, together with vision and touch, is associated with the sense of body ownership. All three can combine or each, on its own, can generate ownership. Related is the sense of agency, the sense of being responsible for one's own actions. In recent times, much progress has been made using neuroimaging techniques to identify the various areas of the brain likely to be responsible for generating these sensations. © 2017 American Physiological Society. Compr Physiol 8:1157-1183, 2018.

Test–retest reliability of wrist joint position sense in healthy adults in a clinical setting

Introduction

Proprioceptive assessments of the wrist inform clinical decision making. In wrist rehabilitation, joint position sense has emerged as one way of assessing conscious proprioception with varying methods and minimal psychometric analysis reported. The purpose of this study was to standardise the wrist joint position sense test method for clinical use and to determine its test–retest reliability in a healthy population.

Methods

Four wrist positions (20° and 45° flexion, 20° and 45° extension) were measured twice in a random order, by a single rater, using a universal goniometer on the same day. The absolute error in degrees between each position and reposition was calculated. For relative reliability analysis, the intraclass correlation coefficient (3,1) was calculated. For absolute reliability the standard error of the measurement was calculated and Bland–Altman plots visually inspected.

Results

Fifty-five healthy volunteers (mean age 31.1 SD±10.25 years) were assessed. The mean absolute error, summarised for all positions for test and retest, was 3.98°. The intraclass correlation coefficients were poor to fair (0.07–0.47), and standard error of the measurement was 2° (rounded) for all positions. The limits of agreement were fairly narrow, and the Bland–Altman plots showed random distribution of errors for each position, therefore the measurement error was clinically acceptable.

Conclusions

The active wrist joint position sense test using goniometry demonstrated poor to fair test–retest reliability and acceptable measurement error in healthy volunteers. The wrist joint position sense angle of 20° flexion was the most reliable.

Relationship between Joint Position Sense, Force Sense, and Muscle Strength and the Impact of Gymnastic Training on Proprioception

The aims of this study were (1) to assess the relationship between joint position (JPS) and force sense (FS) and muscle strength (MS) and (2) to evaluate the impact of long-term gymnastic training on particular proprioception aspects and their correlations. 17 elite adult gymnasts and 24 untrained, matched controls performed an active reproduction (AR) and passive reproduction (PR) task and a force reproduction (FR) task at the elbow joint. Intergroup differences and the relationship between JPS, FS, and MS were evaluated. While there was no difference in AR or PR between groups, absolute error in the control group was higher during the PR task (7.15 ± 2.72°) than during the AR task (3.1 ± 1.93°). Mean relative error in the control group was 61% higher in the elbow extensors than in the elbow flexors during 50% FR, while the gymnast group had similar results in both reciprocal muscles. There was no linear correlation between JPS and FS in either group; however, FR was negatively correlated with antagonist MS. In conclusion, this study found no evidence for a relationship between the accuracy of FS and JPS at the elbow joint. Long-term gymnastic training improves the JPS and FS of the elbow extensors.

Impact of motor task execution on an individual's ability to mirror forearm positions

This work is motivated by our goal of determining why individuals with stroke are impaired when locating their arms in space. We assessed the ability of individuals without neurological impairments to mirror their forearms during various motor tasks so that we could identify baseline performance in an unimpaired population. Nine right-hand dominant participants without neurological impairments mirrored forearm positions bi-directionally (i.e., right forearm mirrors left forearm, vice versa) for three motor tasks (i.e., passive, passive/active, and active) and two position identification modes (i.e., mirroring to a position stored in working memory versus concurrently felt by the opposite arm). During each trial, the participant's reference forearm moved to a flexion ([Formula: see text]) or extension ([Formula: see text]) position, and then, their opposite forearm mirrored the position of their reference forearm. The main finding across all tested conditions is that participants mirrored forearm positions with an average magnitude of error [Formula: see text]. When controlling their forearms' movements (active motor task), participants mirrored forearm positions more accurately by up to, on average, [Formula: see text] at the flexion location than at the extension location. Moreover, participants mirrored forearm positions more accurately by up to, on average, [Formula: see text] when their forearms were moved for them rather than when they controlled their forearms' movements. Task directionality and position identification mode did not significantly affect participant arm mirroring accuracy. These findings are relevant for interpreting in future work the reason why impairments occur, on similar tasks, in individuals with altered motor commands, working memory, and arm impedance, e.g., post-stroke hemiparesis.

The effects of age and amplitude on wrist proprioceptive acuity

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

Modality-specific Changes in Motor Cortex Excitability After Visuo-proprioceptive Realignment

Spatial realignment of visual and proprioceptive estimates of hand position is necessary both to keep the estimates in register over time and to compensate for sensory perturbations. Such realignment affects perceived hand position, which the brain must use to plan hand movements. We would therefore expect visuo-proprioceptive realignment to affect the motor system at some level, but the physiological basis of this interaction is unknown. Here, we asked whether activity in primary motor cortex (M1), a well-known substrate of motor control, shows evidence of change after visuo-proprioceptive realignment. In two sessions each, 32 healthy adults experienced spatially misaligned or veridical visual and proprioceptive information about their static left index finger. Participants indicated perceived finger position with no performance feedback or knowledge of results. Using TMS over the M1 representation of the misaligned finger, we found no average difference between sessions. However, regression analysis indicated that, in the misaligned session only, proprioceptive realignment was linked with a decrease in M1 activity and visual realignment was linked with an increase in M1 activity. Proprioceptive and visual realignment were inversely related to each other. These results suggest that visuo-proprioceptive realignment does indeed have a physiological impact on the motor system. The lack of a between-session mean difference in M1 activity suggests that the basis of the effect is not the multisensory realignment computation itself, independent of modality. Rather, the changes in M1 are consistent with a modality-specific neural mechanism, such as modulation of somatosensory cortex or dorsal stream visual areas that impact M1.

The internal representation of head orientation differs for conscious perception and balance control

KEY POINTS

We tested perceived head-on-feet orientation and the direction of vestibular-evoked balance responses in passively and actively held head-turned postures. The direction of vestibular-evoked balance responses was not aligned with perceived head-on-feet orientation while maintaining prolonged passively held head-turned postures. Furthermore, static visual cues of head-on-feet orientation did not update the estimate of head posture for the balance controller. A prolonged actively held head-turned posture did not elicit a rotation in the direction of the vestibular-evoked balance response despite a significant rotation in perceived angular head posture. It is proposed that conscious perception of head posture and the transformation of vestibular signals for standing balance relying on this head posture are not dependent on the same internal representation. Rather, the balance system may operate under its own sensorimotor principles, which are partly independent from perception.

ABSTRACT

Vestibular signals used for balance control must be integrated with other sensorimotor cues to allow transformation of descending signals according to an internal representation of body configuration. We explored two alternative models of sensorimotor integration that propose (1) a single internal representation of head-on-feet orientation is responsible for perceived postural orientation and standing balance or (2) conscious perception and balance control are driven by separate internal representations. During three experiments, participants stood quietly while passively or actively maintaining a prolonged head-turned posture (>10 min). Throughout the trials, participants intermittently reported their perceived head angular position, and subsequently electrical vestibular stimuli were delivered to elicit whole-body balance responses. Visual recalibration of head-on-feet posture was used to determine whether static visual cues are used to update the internal representation of body configuration for perceived orientation and standing balance. All three experiments involved situations in which the vestibular-evoked balance response was not orthogonal to perceived head-on-feet orientation, regardless of the visual information provided. For prolonged head-turned postures, balance responses consistent with actual head-on-feet posture occurred only during the active condition. Our results indicate that conscious perception of head-on-feet posture and vestibular control of balance do not rely on the same internal representation, but instead treat sensorimotor cues in parallel and may arrive at different conclusions regarding head-on-feet posture. The balance system appears to bypass static visual cues of postural orientation and mainly use other sensorimotor signals of head-on-feet position to transform vestibular signals of head motion, a mechanism appropriate for most daily activities.

Expansion of Perceptual Body Maps Near - But Not Across - The Wrist

Perceiving the external spatial location of touch requires that tactile information about the stimulus location on the skin be integrated with proprioceptive information about the location of the body in external space, a process called tactile spatial remapping. Recent results have suggested that this process relies on a distorted representation of the hand. Here, I investigated whether similar distortions are also found on the forearm and how they are affected by the presence of the wrist joint, which forms a categorical, segmental boundary between the hand and the arm. Participants used a baton to judge the perceived location of touches applied to their left hand or forearm. Similar distortions were apparent on both body parts, with overestimation of distances in the medio-lateral axis compared to the proximo-distal axis. There was no perceptual expansion of distances that crossed the wrist boundary. However, there was increased overestimation of distances near the wrist in the medio-lateral orientation. These results replicate recent findings of a distorted representation of the hand underlying tactile spatial remapping, and show that this effect is not idiosyncratic to the hand, but also affects the forearm. These distortions may be a general characteristic of the mental representation of the arms.

Cutaneous afferent feedback from the posterior ankle contributes to proprioception

Cutaneous mechanoreceptors in skin surrounding joints can respond to the skin strain generated by movement, and thus provide proprioceptive cues. The objective of this experiment was to determine the contribution of skin feedback from the posterior ankle to position sense during passive movements. In 28 healthy adults (12 male), a topical anesthetized (n=14) or placebo cream (n=14) was applied to an area of skin on the posterior ankle that undergoes stretch and compression during ankle dorsi- and plantar-flexion. Position sense was assessed before and after anesthetization using a passive joint matching task (target angles: 6°, 12°, and 18° dorsiflexion and plantar flexion). Results showed that reducing skin feedback caused the perception that the ankles were aligned when the anesthetized ankle was relatively more dorsiflexed, suggesting that posterior ankle skin primarily signals the magnitude of skin stretch. Larger movement into dorsiflexion was likely necessary to provide enough stretch of muscle and surrounding intact skin to compensate for reduced signals from the anesthetized skin region. Reducing skin feedback also increased matching variability during larger movements. These findings suggest that skin feedback from the posterior ankle has a significant contribution to position sense during passive movement. Therefore, the sensitivity of skin surrounding the ankle could be important to consider in populations with reduced peripheral skin sensitivity as a result of ageing or neurological disorders.

Upper Extremity Proprioception After Stroke: Bridging the Gap Between Neuroscience and Rehabilitation

Proprioception is an important aspect of function that is often impaired in the upper extremity following stroke. Unfortunately, neurorehabilitation has few evidence based treatment options for those with proprioceptive deficits. The authors consider potential reasons for this disparity. In doing so, typical assessments and proprioceptive intervention studies are discussed. Relevant evidence from the field of neuroscience is examined. Such evidence may be used to guide the development of targeted interventions for upper extremity proprioceptive deficits after stroke. As researchers become more aware of the impact of proprioceptive deficits on upper extremity motor performance after stroke, it is imperative to find successful rehabilitation interventions to target these deficits and ultimately improve daily function.

The sensory origins of human position sense

KEY POINTS

Position sense at the human forearm can be measured in blindfolded subjects by matching positions of the arms or by a subject pointing to the perceived position of an unseen arm. Effects on position sense tested were: elbow muscle conditioning with a voluntary contraction, muscle vibration, loading the arm and elbow skin stretch. Conditioning contractions and vibration produced errors in a matching task, consistent with the action of muscle spindles as position sensors. Position errors in a pointing task were not consistent with the action of muscle spindles. Loading the arm or skin stretch had no effect in either matching or pointing tasks. It is proposed that there are two kinds of position sense: (i) indicating positions of different body parts relative to one another, using signals from muscle spindles; and (ii) indicating position of the body in extrapersonal space, using signals from exteroceptors, vision, touch and hearing.

ABSTRACT

Human limb position sense can be measured in two ways: in a blindfolded matching task, position of one limb is indicated with the other limb. Alternatively, position of a limb, hidden from view, is indicated with a pointer, moved by pressing a lever. These experiments examined the sensory basis of position sense measured in these two ways. Position errors were measured in 14 subjects after elbow flexors or extensors had been conditioned with a half-maximum voluntary contraction. In agreement with previous studies, in the matching trials, position errors were distributed according to a pattern consistent with the action of muscle spindles as the position sensors. In the pointing trials, all errors lay in the direction of extension of the true position of the hidden arm and their distribution was inconsistent with influences arising in muscle spindles. Vibration of elbow muscles produced an illusion of muscle lengthening during a matching task, while during the pointing task no illusion was present. Finally, the matching-pointing error difference was preserved, even when one arm was loaded with a weight or skin over the elbow was stretched. It is proposed that there are two kinds of position sense. One is signalled by muscle spindles, indicating position of one part of the body relative to another. A second provides information about the position of the body in extrapersonal space and here we hypothesise that exteroceptors, including vision, touch and hearing, acting via a central map of the body, provide the spatial information.

Vibrotactile stimulation of fast-adapting cutaneous afferents from the foot modulates proprioception at the ankle joint

It has previously been shown that cutaneous sensory input from across a broad region of skin can influence proprioception at joints of the hand. The present experiment tested whether cutaneous input from different skin regions across the foot can influence proprioception at the ankle joint. The ability to passively match ankle joint position (17° and 7° plantar flexion and 7° dorsiflexion) was measured while cutaneous vibration was applied to the sole (heel, distal metatarsals) or dorsum of the target foot. Vibration was applied at two different frequencies to preferentially activate Meissner's corpuscles (45 Hz, 80 μm) or Pacinian corpuscles (255 Hz, 10 μm) at amplitudes ∼3 dB above mean perceptual thresholds. Results indicated that cutaneous input from all skin regions across the foot could influence joint-matching error and variability, although the strongest effects were observed with heel vibration. Furthermore, the influence of cutaneous input from each region was modulated by joint angle; in general, vibration had a limited effect on matching in dorsiflexion compared with matching in plantar flexion. Unlike previous results in the upper limb, we found no evidence that Pacinian input exerted a stronger influence on proprioception compared with Meissner input. Findings from this study suggest that fast-adapting cutaneous input from the foot modulates proprioception at the ankle joint in a passive joint-matching task. These results indicate that there is interplay between tactile and proprioceptive signals originating from the foot and ankle.

Proprioceptive Interaction between the Two Arms in a Single-Arm Pointing Task

Proprioceptive signals coming from both arms are used to determine the perceived position of one arm in a two-arm matching task. Here, we examined whether the perceived position of one arm is affected by proprioceptive signals from the other arm in a one-arm pointing task in which participants specified the perceived position of an unseen reference arm with an indicator paddle. Both arms were hidden from the participant’s view throughout the study. In Experiment 1, with both arms placed in front of the body, the participants received 70–80 Hz vibration to the elbow flexors of the reference arm (= right arm) to induce the illusion of elbow extension. This extension illusion was compared with that when the left arm elbow flexors were vibrated or not. The degree of the vibration-induced extension illusion of the right arm was reduced in the presence of left arm vibration. In Experiment 2, we found that this kinesthetic interaction between the two arms did not occur when the left arm was vibrated in an abducted position. In Experiment 3, the vibration-induced extension illusion of one arm was fully developed when this arm was placed at an abducted position, indicating that the brain receives increased proprioceptive input from a vibrated arm even if the arm was abducted. Our results suggest that proprioceptive interaction between the two arms occurs in a one-arm pointing task when the two arms are aligned with one another. The position sense of one arm measured using a pointer appears to include the influences of incoming information from the other arm when both arms were placed in front of the body and parallel to one another.

Age-related deficit in a bimanual joint position matching task is amplitude dependent

The cognitive load associated with joint position sense increases with age but does not necessarily result in impaired performance in a joint position matching task. It is still unclear which factors interact with age to predict matching performance. To test whether movement amplitude and direction are part of such predictors, young and older adults performed a bimanual wrist joint position matching task. Results revealed an age-related deficit when the target limb was positioned far from (25°) the neutral position, but not when close to (15°, 5°) the neutral joint position, irrespective of the direction. These results suggest that the difficulty associated with the comparison of two musculoskeletal states increases towards extreme joint amplitude and that older adults are more vulnerable to this increased difficulty.

How Weight Affects the Perceived Spacing between the Thumb and Fingers during Grasping

We know much about mechanisms determining the perceived size and weight of lifted objects, but little about how these properties of size and weight affect the body representation (e.g. grasp aperture of the hand). Without vision, subjects (n = 16) estimated spacing between fingers and thumb (perceived grasp aperture) while lifting canisters of the same width (6.6cm) but varied weights (300, 600, 900, and 1200 g). Lifts were performed by movement of either the wrist, elbow or shoulder to examine whether lifting with different muscle groups affects the judgement of grasp aperture. Results for perceived grasp aperture were compared with changes in perceived weight of objects of different sizes (5.2, 6.6, and 10 cm) but the same weight (600 g). When canisters of the same width but different weights were lifted, perceived grasp aperture decreased 4.8% [2.2 ‒ 7.4] (mean [95% CI]; P < 0.001) from the lightest to the heaviest canister, no matter how they were lifted. For objects of the same weight but different widths, perceived weight decreased 42.3% [38.2 ‒ 46.4] from narrowest to widest (P < 0.001), as expected from the size-weight illusion. Thus, despite a highly distorted perception of the weight of objects based on their size, we conclude that proprioceptive afferents maintain a reasonably stable perception of the aperture of the grasping hand over a wide range of object weights. Given the small magnitude of this 'weight-grasp aperture' illusion, we propose the brain has access to a relatively stable 'perceptual ruler' to aid the manipulation of different objects.

The role of muscle proprioceptors in human limb position sense: a hypothesis

In this mini-review I have proposed that there are two kinds of position sense, one a sense of the position of one part of the body relative to another, the other a sense of the location in space of our body and its limbs. A common method used to measure position sense is to ask subjects to match with one arm the position adopted by the other. Here all of the evidence points to muscle spindles as the major proprioceptors, with cutaneous receptors acting as proprioceptors providing a supporting role. Other senses such as vision do not play a major role. The sense of localisation in space measured by pointing to the arm, rather than matching its position, I propose, is not served by proprioceptors but by exteroceptors, vision, touch and hearing. Here the afferent input is relayed to sensory areas of the brain, to address the postural schema, a cortical map of the body and limbs, specifying its size and shape. It is here that spatial location is computed. This novel interpretation of position sense as two separate entities has the advantage of proposing new, future experiments and if it is supported by the findings, it will represent an important step forward in our understanding of the central processing of spatial information.

Proprioceptive bimanual test in intrinsic and extrinsic coordinates

Is there any difference between matching the position of the hands by asking the subjects to move them to the same spatial location or to mirror-symmetric locations with respect to the body midline? If the motion of the hands were planned in the extrinsic space, the mirror-symmetric task would imply an additional challenge, because we would need to flip the coordinates of the target on the other side of the workspace. Conversely, if the planning were done in intrinsic coordinates, in order to move both hands to the same spot in the workspace, we should compute different joint angles for each arm. Even if both representations were available to the subjects, the two tasks might lead to different results, providing some cue on the organization of the "body schema". In order to answer such questions, the middle fingertip of the non-dominant hand of a population of healthy subjects was passively moved by a manipulandum to 20 different target locations. Subjects matched these positions with the middle fingertip of their dominant hand. For most subjects, the matching accuracy was higher in the extrinsic modality both in terms of systematic error and variability, even for the target locations in which the configuration of the arms was the same for both modalities. This suggests that the matching performance of the subjects could be determined not only by proprioceptive information but also by the cognitive representation of the task: expressing the goal as reaching for the physical location of the hand in space is apparently more effective than requiring to match the proprioceptive representation of joint angles.

Limb position sense, proprioceptive drift and muscle thixotropy at the human elbow joint

These experiments on the human forearm are based on the hypothesis that drift in the perceived position of a limb over time can be explained by receptor adaptation. Limb position sense was measured in 39 blindfolded subjects using a forearm-matching task. A property of muscle, its thixotropy, a contraction history-dependent passive stiffness, was exploited to place muscle receptors of elbow muscles in a defined state. After the arm had been held flexed and elbow flexors contracted, we observed time-dependent changes in the perceived position of the reference arm by an average of 2.8° in the direction of elbow flexion over 30 s (Experiment 1). The direction of the drift reversed after the arm had been extended and elbow extensors contracted, with a mean shift of 3.5° over 30 s in the direction of elbow extension (Experiment 2). The time-dependent changes could be abolished by conditioning elbow flexors and extensors in the reference arm at the test angle, although this led to large position errors during matching (±10°), depending on how the indicator arm had been conditioned (Experiments 3 and 4). When slack was introduced in the elbow muscles of both arms, by shortening muscles after the conditioning contraction, matching errors became small and there was no drift in position sense (Experiments 5 and 6). These experiments argue for a receptor-based mechanism for proprioceptive drift and suggest that to align the two forearms, the brain monitors the difference between the afferent signals from the two arms.