Identification of unilateral elbow-joint position is impaired by Parkinson's disease

Assessment of joint position sense in active and passive modes with various elbow flexion angles and movement speeds using an isokinetic dynamometer

BACKGROUND

Joint position sense is the ability to detect body segment position in space and is commonly used to represent proprioceptive performance. The isokinetic dynamometer is frequently used to evaluate elbow joint position sense during active and passive reproduction tasks with various testing protocols. However, few studies have reported the performance of joint position sense under different testing conditions.

OBJECTIVE

To compare elbow joint position sense between active and passive reproduction tasks under different matching speeds and reference targets.

DESIGN

A cross-sectional study.

METHODS

Twenty participants without a history of upper-extremity surgery or neuromuscular diseases that affect the joint position sense of the elbow. Active and passive ipsilateral matching tasks were performed at four movement speeds (0.5°/s, 1°/s, 2°/s, and 4°/s) and three reference targets (elbow flexion at 0°-15°, 45°-60°, and 75°-90°), using an isokinetic dynamometer. The absolute and variable errors of each condition were calculated for comparison.

RESULTS

In active matching task with elbow flexion of 0°-15°, the absolute error at 0.5°/s was significantly larger than that at 2°/s and 4°/s, while the variable error at 1°/s was significantly larger than that at 2°/s. However, no differences were found at elbow flexion angles of 45°-60° and 75°-90°. Larger absolute errors were found at 4°/s with three testing angles in passive matching task.

CONCLUSIONS

This study compared the joint position sense errors under various testing conditions in the active and passive reproduction tasks. The movement speeds and target position effects should be considered during evaluation.

Does Impaired Plantar Cutaneous Vibration Perception Contribute to Axial Motor Symptoms in Parkinson's Disease? Effects of Medication and Subthalamic Nucleus Deep Brain Stimulation

OBJECTIVE

To investigate whether impaired plantar cutaneous vibration perception contributes to axial motor symptoms in Parkinson's disease (PD) and whether anti-parkinsonian medication and subthalamic nucleus deep brain stimulation (STN-DBS) show different effects.

METHODS

Three groups were evaluated: PD patients in the medication "on" state (PD-MED), PD patients in the medication "on" state and additionally "on" STN-DBS (PD-MED-DBS), as well as healthy subjects (HS) as reference. Motor performance was analyzed using a pressure distribution platform. Plantar cutaneous vibration perception thresholds (VPT) were investigated using a customized vibration exciter at 30 Hz.

RESULTS

Motor performance of PD-MED and PD-MED-DBS was characterized by greater postural sway, smaller limits of stability ranges, and slower gait due to shorter strides, fewer steps per minute, and broader stride widths compared to HS. Comparing patient groups, PD-MED-DBS showed better overall motor performance than PD-MED, particularly for the functional limits of stability and gait. VPTs were significantly higher for PD-MED compared to those of HS, which suggests impaired plantar cutaneous vibration perception in PD. However, PD-MED-DBS showed less impaired cutaneous vibration perception than PD-MED.

CONCLUSIONS

PD patients suffer from poor motor performance compared to healthy subjects. Anti-parkinsonian medication in tandem with STN-DBS seems to be superior for normalizing axial motor symptoms compared to medication alone. Plantar cutaneous vibration perception is impaired in PD patients, whereas anti-parkinsonian medication together with STN-DBS is superior for normalizing tactile cutaneous perception compared to medication alone. Consequently, based on our results and the findings of the literature, impaired plantar cutaneous vibration perception might contribute to axial motor symptoms in PD.

Body representation underlies response of proprioceptive acuity to repetitive peripheral magnetic stimulation

Proprioceptive acuity is of great significance in basic research exploring a possible neural mechanism of fine motor control and in neurorehabilitation practice promoting motor function recovery of limb-disabled people. Moreover, body representation relies on the integration of multiple somatic sensations, including proprioception that is mainly generated in muscles and tendons of human joints. This study aimed to examine two hypotheses: First, different extension positions of wrist joint have different proprioceptive acuities, which might indicate different body representations of wrist joint in the brain. Second, repetitive peripheral magnetic stimulation (rPMS) applied peripherally to the forearm radial nerve and extensors could change proprioceptive acuity at the wrist joint. Thirty-five healthy participants were recruited then randomly divided into the real stimulation group (n = 15) and the sham stimulation group (n = 20). The participants’ non-dominant side wrist joint position sense was tested at six extension positions within the physiological joint motion range (i.e., 10°, 20°, 30°, 40°, 50°, 60°) both before stimulation and after stimulation. Results showed that proprioceptive bias (arithmetic difference of target position and replicated position) among six extension positions could be divided into lower-extension position (i.e., 10°, 20°, 30°) and higher-extension position (i.e., 40°, 50°, 60°). One session rPMS could influence proprioceptive bias in lower-extension position but not in higher-extension position. However, proprioceptive precision (standard deviation within lower-extension position and higher-extension position) was not influenced. To conclude, proprioceptive bias may vary between different wrist extension positions due to different hand postures being related to changes in body representation, and different functions relating to proprioceptive bias and proprioceptive precision may underlie two aspects of body representation.

Detection of passive movement in lower limb joints is impaired in individuals with Parkinson's disease

OBJECTIVE

Sensory information is crucial when performing daily activities, and Parkinson's disease may diminish sensitivity to sensory cues. This study aimed to examine the detection threshold of passive motion of knee and ankle joints in individuals with Parkinson's disease.

METHODS

Eighteen individuals in the early stages of idiopathic Parkinson's disease (age: 62.7 ± 7.3 years) and 18 healthy matched controls (age: 62.5 ± 7.1 years) first performed a simple reaction time test. Participants were asked to perform ten trials, during which they had to watch a square on a screen and press a button as quickly as possible when the square lit up. Thereafter, the participants were tested for their detection threshold of passive motion of their lower limb joints. Participants were seated in a specially designed chair and their knee or ankle joint was passively moved at a velocity of 0.5º/s. Participants kept their eyes closed and were instructed to press a button as quickly as possible when any joint motion was detected.

RESULTS

Individuals with Parkinson's disease needed more time to perform the reaction time test than did the control participants. Individuals with Parkinson's disease also needed larger angular displacement, even when reaction time was used as a covariate measure, to detect any passive motion, in both knee (0.70º ± 0.20º) and ankle (1.03º ± 0.23º) joints than did the control participants [(0.57º ± 0.20º) and (0.84º ± 0.27º), respectively].

CONCLUSION

Impaired joint proprioception can be observed in the early stages of Parkinson's disease, which may compromise the use of proprioception cues from lower limbs.

Investigation of how accurately individuals with hemiparetic stroke can mirror their forearm positions

Current literature suggests that greater than 50% of survivors of a stroke cannot accurately perceive where their upper extremity is positioned. Our recent work demonstrates that the extent to which this perception is affected can depend on how the task is performed. For example, individuals with stroke who have a deficit in mirroring the position of their passively-placed paretic forearm during a between-arms task may accurately reproduce the position of their actively-controlled paretic forearm during a single-arm task. Moreover, the ability of individuals with various types of unilateral lesions to locate their thumb can depend on whether they reach for their paretic thumb or non-paretic thumb. Consequently, we investigated to what extent the accuracy of individuals post-hemiparetic stroke in mirroring forearm positions on a between-arms task is influenced by various conditions. Eighteen participants with hemiparetic stroke rotated their reference forearm to a target position, and then rotated their opposite forearm to concurrently mirror the position of their reference forearm. This task was performed when participants referenced each forearm (paretic, non-paretic) at two target positions (extension, flexion) for two modes of limb control (passive, active). We quantified for every testing scenario of each participant their position-mirroring error. The number of times for which participants were classified as having a deficit was least when mirroring forearm positions at the flexed position when referencing their non-paretic forearm. Additionally, the difference in the magnitude of errors when participants referenced each arm was greater during active than passive movements. Findings from this study provide further evidence that the accuracy with which individuals post stroke perceive the position of their limbs can depend on how a task is performed. Factors to consider include whether movements are active versus passive, which limb is referenced, and where the limb is positioned.

Proprioceptive recalibration following implicit visuomotor adaptation is preserved in Parkinson's disease

Individuals with Parkinson's disease (PD) and healthy adults demonstrate similar levels of visuomotor adaptation provided that the distortion is small or introduced gradually, and hence, implicit processes are engaged. Recently, implicit processes underlying visuomotor adaptation in healthy individuals have been proposed to include proprioceptive recalibration (i.e., shifts in one's proprioceptive sense of felt hand position to match the visual estimate of their hand experienced during reaches with altered visual feedback of the hand). In the current study, we asked if proprioceptive recalibration is preserved in PD patients. PD patients tested during their "off" and "on" medication states and age-matched healthy controls reached to visual targets, while visual feedback of their unseen hand was gradually rotated 30° clockwise or translated 4 cm rightwards of their actual hand trajectory. As expected, PD patients and controls produced significant reach aftereffects, indicating visuomotor adaptation after reaching with the gradually introduced visuomotor distortions. More importantly, following visuomotor adaptation, both patients and controls showed recalibration in hand position estimates, and the magnitude of this recalibration was comparable between PD patients and controls. No differences for any measures assessed were observed across medication status (i.e., PD off vs PD on). Results reveal that patients are able to adjust their sensorimotor mappings and recalibrate proprioception following adaptation to a gradually introduced visuomotor distortion, and that dopaminergic intervention does not affect this proprioceptive recalibration. These results suggest that proprioceptive recalibration does not involve striatal dopaminergic pathways and may contribute to the preserved visuomotor adaptation that arises implicitly in PD patients.

Stability of Action and Kinesthetic Perception in Parkinson's Disease

We present a review of action and perception stability within the theoretical framework based on the idea of control with spatial referent coordinates for the effectors at a number of hierarchical levels. Stability of salient variables is ensured by synergies, neurophysiological structures that act in multi-dimensional spaces of elemental variables and limit variance to the uncontrolled manifold during action and iso-perceptual manifold during perception. Patients with Parkinson’s disease show impaired synergic control reflected in poor stability (low synergy indices) and poor agility (low indices of anticipatory synergy adjustments prior to planned quick actions). They also show impaired perception across modalities, including kinesthetic perception. We suggest that poor stability at the level of referent coordinates can be the dominant factor leading to poor stability of percepts.

Somatosensory Training Improves Proprioception and Untrained Motor Function in Parkinson's Disease

Background: Proprioceptive impairment is a common feature of Parkinson's disease (PD). Proprioceptive function is only partially restored with anti-parkinsonian medication or deep brain stimulation. Behavioral exercises focusing on somatosensation have been promoted to overcome this therapeutic gap. However, conclusive evidence on the effectiveness of such somatosensory-focused behavioral training for improving somatosensory function is lacking. Moreover, it is unclear, if such training has any effect on motor performance in PD.

Objective: To investigate, whether proprioception improves with a somatosensory focused, robot-aided training in people with PD (PWPs), and whether enhanced proprioception translates to improved motor performance.

Method: Thirteen PWPs of mild-moderate clinical severity were assessed and trained ON medication using a robotic wrist exoskeleton. Thirteen healthy elderly participants served as controls. Training involved making increasingly accurate, continuous, precise small amplitude wrist flexion/extension movements. Wrist position sense acuity, as a marker of proprioception function, and spatial error during wrist pointing, as a marker of untrained motor performance, were recorded twice before and once after training. Functional hand writing kinematics exhibited during training were evaluated in the PD group for determining training-induced changes.

Results: Training improved position sense acuity in all PWPs (mean change: 28%; p < 0.001) and healthy controls (mean change: 23%; p < 0.01). Second, 10/13 PD participants and 10/13 healthy control participants had reduced spatial movement error in the untrained wrist pointing task after training. Third, spatial error for the functional handwriting tasks (line tracing and tracking) did not improve with training in the PD group.

Conclusion: Proprioceptive function in mild to moderate PD is trainable and improves with a somatosensory-focused motor training. Learning showed a local transfer within the trained joint degree-of-freedom as improved spatial accuracy in an unpracticed motor task. No learning gains were observed for the untrained functional handwriting task, indicating that training may be specific to the trained joint degree-of-freedom.

Ability of individuals with chronic hemiparetic stroke to locate their forearms during single-arm and between-arms tasks

Background

According to between-arms assessments, more than 50% of individuals with stroke have an impaired position sense. Our previous work, which employed a clinical assessment and slightly differing tasks, indicates that individuals who have a deficit on a between-forearms position-localization task do not necessarily have a deficit on a single-forearm position-localization task.

Objective

Our goal here was to, using robotics tools, determine whether individuals with stroke who have a deficit when matching forearm positions within an arm also have a deficit when mirroring forearm positions between arms, independent of the arm that leads the task.

Methods

Eighteen participants with chronic hemiparetic stroke and nine controls completed a single-arm position-matching experiment and between-arms position-mirroring experiment. For each experiment, the reference forearm (left/right) passively rotated about the elbow joint to a reference target location (flexion/extension), and then the participant actively rotated their same/opposite forearm to match/mirror the reference forearm’s position. Participants with stroke were classified as having a position-matching/-mirroring deficit based on a quantitative threshold that was derived from the controls’ data.

Results

On our single-arm task, one participant with stroke was classified as having a position-matching deficit with a mean magnitude of error greater than 10.7° when referencing their paretic arm. Position-matching ability did not significantly differ for the controls and the remaining seventeen participants with stroke. On our between-arms task, seven participants with stroke were classified as having a position-mirroring deficit with a mean magnitude of error greater than 10.1°. Position-mirroring accuracy was worse for these participants with stroke, when referencing their paretic arm, than the controls.

Concluding remark

Findings underscore the need for assessing within-arm position-matching deficits, in addition to between-arms position-mirroring deficits when referencing each arm, to comprehensively evaluate an individual’s ability to locate their forearm(s).

Actual and Illusory Perception in Parkinson's Disease and Dystonia: A Narrative Review

Sensory information is continuously processed so as to allow behavior to be adjusted according to environmental changes. Before sensory information reaches the cortex, a number of subcortical neural structures select the relevant information to send to be consciously processed. In recent decades, several studies have shown that the pathophysiological mechanisms underlying movement disorders such as Parkinson's disease (PD) and dystonia involve sensory processing abnormalities related to proprioceptive and tactile information. These abnormalities emerge from psychophysical testing, mainly temporal discrimination, as well as from experimental paradigms based on bodily illusions. Although the link between proprioception and movement may be unequivocal, how temporal tactile information abnormalities and bodily illusions relate to motor disturbances in PD and dystonia is still a matter of debate. This review considers the role of altered sensory processing in the pathophysiology of movement disorders, focusing on how sensory alteration patterns differ between PD and dystonia. We also discuss the evidence available and the potential for developing new therapeutic strategies based on the manipulation of multi-sensory information and bodily illusions in patients with these movement disorders.

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.

A robot-aided visuo-motor training that improves proprioception and spatial accuracy of untrained movement

Proprioceptive function can become enhanced during motor learning. Yet, we have incomplete knowledge to what extent proprioceptive function is trainable and how a training that enhances proprioception may influence performance in untrained motor skills. To address this knowledge gap, healthy young adults (N = 14) trained in a visuomotor task that required learners to make increasingly accurate wrist movements. Using a robotic exoskeleton coupled with a virtual visual environment, participants tilted a virtual table through continuous wrist flexion/extension movements with the goal to position a rolling ball on table into a target. With learning progress, the level of difficulty increased by altering the virtual ball mechanics and the gain between joint movement and ball velocity. Before and after training, wrist position sense acuity and spatial movement accuracy in an untrained, discrete wrist-pointing task was assessed using the same robot. All participants showed evidence of proprioceptive-motor learning. Mean position sense discrimination threshold improved by 34%. Wrist movement accuracy in the untrained pointing task improved by 27% in 13/14 participants. This demonstrates that a short sensorimotor training challenging proprioception can a) effectively enhance proprioceptive acuity and b) improve the accuracy of untrained movement. These findings provide a scientific basis for applying such somatosensory-based motor training to clinical populations with known proprioceptive dysfunction to enhance sensorimotor performance.

Resting-state functional reorganization in Parkinson's disease: An activation likelihood estimation meta-analysis

Parkinson's disease (PD) is a common progressive neurodegenerative disorder. Studies using resting-state functional magnetic resonance imaging (fMRI) to investigate underlying pathophysiology of motor and non-motor symptoms in PD yielded largely inconsistent results. This quantitative neuroimaging meta-analysis aims to identify consistent abnormal intrinsic functional patterns in PD across studies. We used PubMed to retrieve suitable resting-state studies and stereotactic data were extracted from 28 individual between-group comparisons. Convergence across their findings was tested using the activation likelihood estimation (ALE) approach. We found convergent evidence for intrinsic functional disturbances in bilateral inferior parietal lobule (IPL) and the supramarginal gyrus in PD patients compared to healthy subjects. In follow-up task-based and task-independent functional connectivity (FC) analyses using two independent healthy subject data sets, we found that the regions showing convergent aberrations in PD formed an interconnected network mainly with the default mode network (DMN). Behavioral characterization of these regions using the BrainMap database suggested associated dysfunction of perception and executive processes. Taken together, our findings highlight the role of parietal cortex in the pathophysiology of PD.

Evaluation of Knee Proprioception and Factors Related to Parkinson's Disease

Background. Changes in proprioception may contribute to postural instability in individuals with neurological disorders. Objectives. Evaluate proprioception in the lower limbs of patients with Parkinson's disease (PD) and the association between proprioception and cognitive ability, motor symptoms, postural instability, and disease severity. Methods. This is a cross-sectional, controlled study that evaluated proprioception in PD patients and healthy age- and sex-matched individuals. Kinetic postural proprioception of the knee was evaluated using an isokinetic dynamometer (Biodex® Multi-Joint System 4 Pro). Participants were evaluated using the Montreal Cognitive Assessment (MoCA), the Hoehn and Yahr rating scale and postural instability (pull test and stabilometric analysis), and motor function (UPDRS-III) tests. Results. A total of 40 individuals were enrolled in the study: 20 PD patients and 20 healthy controls (CG). The PD patients had higher angular errors on the proprioceptive ratings than the CG participants (p = 0.002). Oscillations of the center of pressure (p = 0.002) were higher in individuals with PD than in the controls. Proprioceptive errors in the PD patients were associated with the presence of tremors as the dominant symptom and more impaired motor performance. Conclusion. These findings show that individuals with PD have proprioceptive deficits, which are related to decreased cognitive ability and impaired motor symptoms.

A central processing sensory deficit with Parkinson's disease

Parkinson's disease (PD) is a progressive degenerative disease manifested by tremor, rigidity, bradykinesia, and postural instability. Deficits in proprioceptive integration are prevalent in individuals with PD, even at early stages of the disease. These deficits have been demonstrated primarily during investigations of reaching. Here, we investigated how PD affects sensory fusion of multiple modalities during upright standing. We simultaneously perturbed upright stance with visual, vestibular, and proprioceptive stimulation, to understand how these modalities are reweighted so that overall feedback remains suited to stabilizing upright stance in individuals with PD. Eight individuals with PD stood in a visual cave with a moving visual scene at 0.2 Hz while an 80-Hz vibratory stimulus was applied bilaterally to their Achilles tendons (stimulus turns on-off at 0.28 Hz) and a ±1 mA bilateral monopolar galvanic stimulus was applied at 0.36 Hz. The visual stimulus was presented at different amplitudes (0.2°, 0.8° rotation about ankle axis) to measure: the change in gain (weighting) to vision, an intramodal effect; and a simultaneous change in gain to vibration and galvanic stimulation, both intermodal effects. Trunk/leg gain relative to vision decreased when visual amplitude was increased, reflecting an intramodal visual effect. In contrast, when vibration was turned on/off, leg gain relative to vision was equivalent in individuals with PD, indicating no reweighting of visual information when proprioception was disrupted through vibration (i.e., no intermodal effect). Trunk and leg angle gain relative to GVS also showed no reweighting in individuals with PD. These results are in contrast to previous results with healthy adults, who showed clear intermodal effects in the same paradigm, suggesting that individuals with PD not only have a proprioceptive deficit during standing, but also have a cross-modal sensory fusion deficit that is crucial for upright stance control.

Dynamic High-Cadence Cycling Improves Motor Symptoms in Parkinson's Disease

RATIONALE

Individuals with Parkinson's disease (PD) often have deficits in kinesthesia. There is a need for rehabilitation interventions that improve these kinesthetic deficits. Forced (tandem) cycling at a high cadence improves motor function. However, tandem cycling is difficult to implement in a rehabilitation setting.

OBJECTIVE

To construct an instrumented, motored cycle and to examine if high cadence dynamic cycling promotes improvements in motor function.

METHOD

This motored cycle had two different modes: dynamic and static cycling. In dynamic mode, the motor maintained 75-85 rpm. In static mode, the rider determined the pedaling cadence. UPDRS Motor III and Timed Up and Go (TUG) were used to assess changes in motor function after three cycling sessions.

RESULTS

Individuals in the static group showed a lower cadence but a higher power, torque and heart rate than the dynamic group. UPDRS score showed a significant 13.9% improvement in the dynamic group and only a 0.9% improvement in the static group. There was also a 16.5% improvement in TUG time in the dynamic group but only an 8% improvement in the static group.

CONCLUSION

These findings show that dynamic cycling can improve PD motor function and that activation of proprioceptors with a high cadence but variable pattern may be important for motor improvements in PD.

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.

Elbow joint position sense after total elbow arthroplasty

BACKGROUND

Multiple human experiments have shown that articular lesions can have a negative effect on proprioception. The influence of total elbow arthroplasty on joint position sense has not been reported so far. The purpose of the study was to evaluate proprioception, defined as a joint position sense, after total elbow arthroplasty.

METHODS

The study included 16 patients with unilateral semiconstrained linked total elbow arthroplasty and 21 healthy volunteers. The evaluation included measurement of active and passive reproduction of joint position sense of both elbows after surgery and the control groups. Reference angles included extension to 50° and 70° and flexion to 110°. We also assessed function of the elbow in arthroplasty group using the Mayo Elbow Performance Score, the Disability of the Arm, Shoulder and Hand score, and a visual analog scale for pain level.

RESULTS

The average value of error of passive reproduction of joint position for elbows after arthroplasty was significantly inferior for all evaluated positions compared with the contralateral elbow and with the control group, respectively, at 110° flexion: 4.3°, 2.7°, and 3.2°; at 70° extension: 4.9°, 2.9°, and 2.7°; and at 50° extension: 6.3°, 3.8°, and 3.8°. The average value of error of active reproduction of joint position for the arthroplasty group was also significantly inferior, respectively, at 110° flexion: 3.5°, 1.9° and 2°; and at 50° extension: 4.4°, 3.3°, and 3°.

CONCLUSION

Proprioception in elbows that undergo total arthroplasty is significantly inferior compared with the contralateral site of the patient and in the healthy control group.

Variability in cadence during forced cycling predicts motor improvement in individuals with Parkinson's disease

Variability in severity and progression of Parkinson's disease symptoms makes it challenging to design therapy interventions that provide maximal benefit. Previous studies showed that forced cycling, at greater pedaling rates, results in greater improvements in motor function than voluntary cycling. The precise mechanism for differences in function following exercise is unknown. We examined the complexity of biomechanical and physiological features of forced and voluntary cycling and correlated these features to improvements in motor function as measured by the Unified Parkinson's Disease Rating Scale (UPDRS). Heart rate, cadence, and power were analyzed using entropy signal processing techniques. Pattern variability in heart rate and power were greater in the voluntary group when compared to forced group. In contrast, variability in cadence was higher during forced cycling. UPDRS Motor III scores predicted from the pattern variability data were highly correlated to measured scores in the forced group. This study shows how time series analysis methods of biomechanical and physiological parameters of exercise can be used to predict improvements in motor function. This knowledge will be important in the development of optimal exercise-based rehabilitation programs for Parkinson's disease.

Light and heavy touch reduces postural sway and modifies axial tone in Parkinson's disease

BACKGROUND

Light touch with a stable object reduces postural sway by increasing axial postural tone in healthy subjects. However, it is unknown whether subjects with Parkinson's disease (PD), who have more postural sway and higher axial postural tone than healthy subjects, can benefit from haptic touch.

OBJECTIVE

To investigate the effect of light and heavy touch on postural stability and hip tone in subjects with PD.

METHODS

Fourteen subjects with mid-stage PD and 14 healthy control subjects were evaluated during quiet standing with eyes closed with their arms (a) crossed, (b) lightly touching a fixed rigid bar in front of them, and (c) firmly gripping the bar. Postural sway was measured with a forceplate, and axial hip tone was quantified using a unique device that measures the resistance of the hips to yaw rotation while maintaining active stance.

RESULTS

Subjects with PD significantly decreased their postural sway with light or heavy touch (P < .001 vs arms crossed), similarly as control subjects. Without touch, hip tone was larger in PD subjects. With touch, however, tone values were similar in both groups. This change in hip tone with touch was highly correlated with the initial amount of tone (PD, r = -.72 to -.95; controls, r = -.74 to -.85).

CONCLUSIONS

The authors showed, for the first time, that subjects with PD benefit from touch similarly to control subjects and that despite higher axial postural tone, PD subjects are able to modulate their tone with touch. Future studies should investigate the complex relationship between touch and postural tone.

No proprioceptive deficits in autism despite movement-related sensory and execution impairments

Autism spectrum disorder (ASD) often involves sensory and motor problems, yet the proprioceptive sense of limb position has not been directly assessed. We used three tasks to assess proprioception in adolescents with ASD who had motor and sensory perceptual abnormalities, and compared them to age- and IQ-matched controls. Results showed no group differences in proprioceptive accuracy or precision during active or passive tasks. Both groups showed (a) biases in elbow angle accuracy that varied with joint position, (b) improved elbow angle precision for active versus passive tasks, and (c) improved precision for a fingertip versus elbow angle estimation task. Thus, a primary proprioceptive deficit may not contribute to sensorimotor deficits in ASD. Abnormalities may arise at later sensory processing stages.

Proprioceptive deficits in Parkinson's disease patients with freezing of gait

Recent research has proposed that proprioceptive deficits may exist in Parkinson's disease (PD); however, proprioception has not been studied in those who experience freezing of gait (FOG). Proprioception was investigated through stimulation of proprioceptive receptors via patellar tendon vibration. In a force matching task to either 10% or 30% maximal voluntary contraction, response to vibration with and without vision of a force target was compared between 15 PD with FOG (PD-FOG), 16 PD without FOG (PD non-FOG), and 15 non-PD control participants (Controls). In a 15-s trial, vision of the target was provided for the first 10 s but in the last 5 s, four conditions were possible: (i) vision, no vibration; (ii) vision, vibration; (iii) no vision, no vibration; or (iv) no vision, vibration. The expected healthy response to vibration was an overshoot of the target. Controls and PD non-FOG did not perform significantly different with or without: vibration or vision. PD-FOG performed similarly to Controls and PD non-FOG in the baseline condition (i). Errors by PD-FOG on the other conditions (ii-iv) were significantly different from the baseline condition but were not significantly different from each other. The PD-FOG group significantly undershot the target when vibration was added [F((2,36))=4.8376, P<0.02] and when vision was removed [F((2,36))=4.8376, P<0.02]. It is suggested that any deviation from normal sensory availability contributes to severe deficits in PD-FOG.

Walking in circles: navigation deficits from Parkinson's disease but not from cerebellar ataxia

Little is known on the role of neuronal structures for spatial navigation. Our goal was to examine how Parkinson's disease (PD) and cerebellar ataxia, as human lesion models of the basal ganglia and cerebellum, affect spatial navigation round a circular walking path, blindfolded. Twelve subjects with idiopathic PD (ON and OFF medication), eight subjects with cerebellar ataxia and a control group of 20 age-matched healthy subjects participated. All groups performed well when walking around the circle with eyes open. In the eyes-closed condition, control subjects overshot the outlined trajectory but returned to their initial position, thus walking a further distance with eyes closed than with eyes open. When OFF medication, PD subjects navigated a larger radius than controls with eyes closed. When ON levodopa, PD subjects walked a similar distance as controls but with even larger errors in endpoint. Surprisingly, cerebellar patients navigated the circular walking task in the eyes closed condition with even more accuracy (i.e. following the outlined circle) than control and PD subjects. We conclude that blindfolded navigation around a previously seen circle requires intact basal ganglia, but not cerebellar input.

The neural basis of central proprioceptive processing in older versus younger adults: an important sensory role for right putamen

Our sense of body position and movement independent of vision (i.e., proprioception) relies on muscle spindle feedback and is vital for performing motor acts. In this study, we first sought to elucidate age-related differences in the central processing of proprioceptive information by stimulating foot muscle spindles and by measuring neural activation with functional magnetic resonance imaging. We found that healthy older adults activated a similar, distributed network of primary somatosensory and secondary-associative cortical brain regions as young individuals during the vibration-induced muscle spindle stimulation. A significant decrease in neural activity was also found in a cluster of right putamen voxels for the older age group when compared with the younger age group. Given these differences, we performed two additional analyses within each group that quantified the degree to which age-dependent activity was related to (1) brain structure and (2) a behavioral measure of proprioceptive ability. Using diffusion tensor imaging, older (but not younger) adults with higher mean fractional anisotropy were found to have increased right putamen neural activity. Age-dependent right putamen activity seen during tendon vibration was also correlated with a behavioral test of proprioceptive ability measuring ankle joint position sense in both young and old age groups. Partial correlation tests determined that the relationship between elderly joint position sense and neural activity in right putamen was mediated by brain structure, but not vice versa. These results suggest that structural differences within the right putamen are related to reduced activation in the elderly and potentially serve as biomarker of proprioceptive sensibility in older adults.

Proprioceptive acuity assessment via joint position matching: from basic science to general practice

Over the past several decades, studies of use-dependent plasticity have demonstrated a critical role for proprioceptive feedback in the reorganization, and subsequent recovery, of neuromotor systems. As such, an increasing emphasis has been placed on tests of proprioceptive acuity in both the clinic and the laboratory. One test that has garnered particular interest is joint position matching, whereby individuals must replicate a reference joint angle in the absence of vision (ie, using proprioceptive information). On the surface, this test might seem straightforward in nature. However, the present perspective article informs therapists and researchers alike of multiple insights gained from a recent series of position matching studies by the author and colleagues. In particular, 5 factors are outlined that can assist clinicians in developing well-informed opinions regarding the outcomes of tests of position matching abilities. This information should allow for enhanced diagnosis of proprioceptive deficits within clinical settings in the future.

Axial kinesthesia is impaired in Parkinson's disease: effects of levodopa

Integration of sensory and motor inputs has been shown to be impaired in appendicular muscles and joints of Parkinson's disease (PD) patients. As PD advances, axial symptoms such as gait and balance impairments appear, which often progresses to complete inability stand or walk unaided. The current study evaluates kinesthesia in the axial musculature of PD patients during active postural control to determine whether impairments similar to those found in the appendages are also present in the hip and trunk. Using axial twisting, we quantified the detection threshold and directional accuracy of the hip relative to the feet (i.e. Hip Kinesthesia) and the hip relative to the shoulders (i.e. Trunk Kinesthesia). The relation of kinesthetic threshold to disease progression as measured by UPDRS and the effect of levodopa treatment on kinesthesia were assessed in 12 PD compared to age-matched controls. Subjects stood unaided while passively twisted at a very low constant rotational velocity (1 degrees /s). The results showed that accuracy in determining the direction of axial twisting was reduced in PD relative to healthy control subjects in the hip (PD-ON: 81%; PD-OFF: 91%; CTL=96%) and trunk (PD-ON: 81%; PD-OFF: 88%; CTL=95%). Thresholds for perception of axial twisting were increased when PD subjects were ON levodopa versus OFF in both the hip (p<0.01) and the trunk (p<0.05). The magnitude of decrease in sensitivity due to being ON levodopa was significantly correlated with the increase in UPDRS motor scores (Hip: r=0.90, p<0.01 and Trunk: r=0.60, p<0.05). This effect was not significantly correlated with equivalent levodopa dosage. PD subjects with disease onset on the left side of their body showed significantly higher axial thresholds than subjects with right PD onset (p<0.05). In conclusion, deficits in axial kinesthesia seem to contribute to the functional impairments of posture and locomotion in PD. Although levodopa has been shown to improve appendicular kinesthesia, we observed the opposite in the body axis. These findings underscore the dissociable neurophysiological circuits and dopaminergic pathways that are known to innervate these functionally distinct muscle groups.

Proprioception and motor control in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder that leads to a progressive decline in motor function. Growing evidence indicates that PD patients also experience an array of sensory problems that negatively impact motor function. This is especially true for proprioceptive deficits, which profoundly degrade motor performance. This review specifically address the relation between proprioception and motor impairments in PD. It is structured around 4 themes: (a) It examines whether the sensitivity of kinaesthetic perception, which is based on proprioceptive inputs, is actually altered in PD. (b) It discusses whether failed processes of proprioceptive-motor integration are central to the motor problems in PD. (c) It presents recent findings focusing on the link between the proprioception and the balance problems in PD. And (d) it discusses the current state of knowledge of how levodopa medication and deep brain stimulation affect proprioceptive and motor function in PD. The authors conclude that a failure to evaluate and to map proprioceptive information onto voluntary and reflexive motor commands is an integral part of the observed motor symptoms in PD.

Elbow joint position sense following brachial plexus palsy treated with double free muscle transfer

PURPOSE

Restoration of elbow flexion is the highest priority for brachial plexus reconstruction, and its reconstructive strategy is well established. The purpose of this article is to report elbow joint position sense (JPS) after double free muscle transfer (DFMT) for complete paralysis of brachial plexus.

METHODS

Thirteen patients with complete brachial plexus paralysis who were treated with DFMT underwent evaluation of elbow JPS. JPS was measured as the subject's ability to actively reproduce a previously presented position of the elbow joint (target angle). We calculated the difference between target and reproduced angle and defined this as the absolute error (AE). Ten healthy control subjects participated in this study.

RESULTS

In control subjects, mean AE measured 4 degrees +/- 1 degree at the target angle of 60 degrees and 4 degrees +/- 2 degrees at 80 degrees. After DFMT, patients' mean AE measured 5 degrees +/- 2 degrees at the target angle of 60 degrees and 5 degrees +/- 3 degrees at 80 degrees. There was no statistical difference between the control and DFMT groups at target angles of 60 degrees and 80 degrees.

CONCLUSIONS

Patients with complete paralysis of the brachial plexus had evidence of elbow JPS after successful restoration of elbow flexion after DFMT. Although this study provides us with useful information regarding the perception of elbow JPS, further study is necessary to confirm the exact mechanism of perception of elbow JPS.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Where is your arm? Variations in proprioception across space and tasks

The sense of limb position is crucial for movement control and environmental interactions. Our understanding of this fundamental proprioceptive process, however, is limited. For example, little is known about the accuracy of arm proprioception: Does it vary with changes in arm configuration, since some peripheral receptors are engaged only when joints move toward extreme angles? Are these variations consistent across different tasks? Does proprioceptive ability change depending on what we try to localize (e.g., fingertip position vs. elbow angle)? We used a robot exoskeleton to study proprioception in 14 arm configurations across three tasks, asking healthy subjects to 1) match a pointer to elbow angles after passive movements, 2) match a pointer to fingertip positions after passive movements, and 3) actively match their elbow angle to a pointer. Across all three tasks, subjects overestimated more extreme joint positions; this may be due to peripheral sensory signals biasing estimates as a safety mechanism to prevent injury. We also found that elbow angle estimates were more precise when used to judge fingertip position versus directly reported, suggesting that the brain has better access to limb endpoint position than joint angles. Finally, precision of elbow angle estimates improved in active versus passive movements, corroborating work showing that efference copies of motor commands and alpha-gamma motor neuron coactivation contribute to proprioceptive estimates. In sum, we have uncovered fundamental aspects of normal proprioceptive processing, demonstrating not only predictable biases that are dependent on joint configuration and independent of task but also improved precision when integrating information across joints.

Haptic perception of object curvature in Parkinson's disease

Background

The haptic perception of the curvature of an object is essential for adequate object manipulation and critical for our guidance of actions. This study investigated how the ability to perceive the curvature of an object is altered by Parkinson's disease (PD).

Methodology/Principal Findings

Eight healthy subjects and 11 patients with mild to moderate PD had to judge, without vision, the curvature of a virtual “box” created by a robotic manipulandum. Their hands were either moved passively along a defined curved path or they actively explored the curved curvature of a virtual wall. The curvature was either concave or convex (bulging to the left or right) and was judged in two locations of the hand workspace–a left workspace location, where the curved hand path was associated with curved shoulder and elbow joint paths, and a right workspace location in which these joint paths were nearly linear. After exploring the curvature of the virtual object, subjects had to judge whether the curvature was concave or convex. Based on these data, thresholds for curvature sensitivity were established. The main findings of the study are: First, 9 out 11 PD patients (82%) showed elevated thresholds for detecting convex curvatures in at least one test condition. The respective median threshold for the PD group was increased by 343% when compared to the control group. Second, when distal hand paths became less associated with proximal joint paths (right workspace), haptic acuity was reduced substantially in both groups. Third, sensitivity to hand trajectory curvature was not improved during active exploration in either group.

Conclusion/Significance

Our data demonstrate that PD is associated with a decreased acuity of the haptic sense, which may occur already at an early stage of the disease.

Impairment of complex upper limb motor function in de novo Parkinson's disease

The aim of the present study was to evaluate complex upper limb motor function in newly diagnosed, untreated Parkinson's disease (PD) patients. Four different unimanual upper limb motor tasks were applied to 13 newly diagnosed, untreated PD patients and 13 age- and sex-matched controls. In a handwriting task, PD patients had significantly reduced sentence length and writing velocity, and decreasing letter height in the course of writing. Furthermore, PD patients performed an aiming task slower with than without target, and showed increased transposition in a pointing task. The results of this study extend previous observations of impaired complex upper limb movements to newly diagnosed, untreated PD patients.

Human limb-specific and non-limb-specific brain representations during kinesthetic illusory movements of the upper and lower extremities

Sensing movements of the upper and lower extremities is important in controlling whole-body movements. We have shown that kinesthetic illusory hand movements activate motor areas and right-sided fronto-parietal cortices. We investigated whether illusions for the upper and lower extremities, i.e. right or left hand or foot, activate the somatotopical sections of motor areas, and if an illusion for each limb engages the right-sided cortices. We scanned the brain activity of 19 blindfolded right-handed participants using functional magnetic resonance imaging (fMRI) while they experienced an illusion for each limb elicited by vibrating its tendon at 110 Hz (ILLUSION). As a control, we applied identical stimuli to the skin over a nearby bone, which does not elicit illusions (VIBRATION). The illusory movement (ILLUSION vs. VIBRATION) of each immobile limb activated limb-specific sections of the contralateral motor cortex (along with somatosensory area 3a), dorsal premotor cortex (PMD), supplementary motor area (SMA), cingulate motor area (CMA), and the ipsilateral cerebellum, which normally participate in execution of movements of the corresponding limb. We found complex non-limb-specific representations in rostral parts of the bilateral SMA and CMA, and illusions for all limbs consistently engaged concentrated regions in right-sided fronto-parietal cortices and basal ganglia. This study demonstrated complete sets of brain representations related to kinesthetic processing of single-joint movements of the four human extremities. The kinesthetic function of motor areas suggests their importance in somatic perception of limb movement, and the non-limb-specific representations indicate high-order kinesthetic processing related to human somatic perception of one's own body.

The perception of passive motion in Parkinson's disease

The perception of limb motion is a kinaesthetic property that is essential for voluntary motor control. This study examined the ability of patients with Parkinson's disease (PD) to detect the velocity of a passively moved limb. Eight patients with mild to moderate PD and eight age-matched healthy controls participated. They placed their forearm on a padded splint of a passive motion apparatus, which horizontally extended or flexed the elbow joint at velocities between 1.65 and 0.075 degrees /s (in steps of 0.15 degrees /s). Passive movement persisted until subjects detected arm motion and pressed a trigger held in the hand of their non-tested arm. Time until detection and associated arm displacement were recorded and subsequently adjusted for each subject's reaction time. We found that PD patients needed significantly larger limb displacements before they could judge the presence of passive motion. With decreasing passive motion velocity the detection time increased exponentially in both groups. Yet, the mean detection times of the PD group were 92-166% higher than in the control group for each of the 12 tested velocity conditions. Five of the eight patients were on Parkinsonian medication when tested. Yet, the degree of impairment in the PD group did not correlate significantly with the patients' levodopa equivalent dosage. Our results demonstrate that PD patients were impaired in the detection of passive forearm movements. This study complements a growing body of evidence indicating that various aspects of kinaesthesis (position sense, weight perception, passive motion sense) are affected even at early stages of PD. The impaired processing of proprioceptive signals likely contributes to motor symptoms in PD.

Impaired vertical postural control and proprioceptive integration deficits in Parkinson's disease

The aim of the present study was to investigate how the orientation and stabilization components of postural control may be affected as the result of the impaired proprioceptive integration possibly occurring in Parkinson's disease. To determine the proprioceptive contribution to postural control, parkinsonian patients and control subjects were asked to maintain vertical stance while very slow sinusoidal oscillations were being applied in the lateral and antero-posterior planes to the platform on which they were standing. The amplitude and frequency of their movements were kept below the semicircular canal perception threshold. Data were collected with the ELITE automatic motion analyzer and the two postural components (orientation and segmental stabilization) were analyzed at head and trunk levels while the subjects were performing the task with their eyes open and closed. The results show that 1) the parkinsonian groups' performances were affected in terms of both the postural orientation and stabilization components in comparison with the control group, 2) the use of vision improved the parkinsonian patients' postural performances, and 3) both parkinsonian patients and control subjects achieved better postural performances when antero-posterior perturbations rather than lateral perturbations were applied to the foot support. These results suggest that Parkinson's disease is associated with proprioceptive impairment, which may be an important factor contributing to these patients' postural deficits. On the basis of these results, the visual dependence observed in parkinsonian patients is re-defined as an adaptive strategy partly compensating for the impaired proprioception.

Task-dependent asymmetries in the utilization of proprioceptive feedback for goal-directed movement

Whereas the majority of studies regarding upper limb asymmetries in motor performance have focused on preferred arm dominance for producing motor output, studies exploring the role of sensory feedback have suggested that the preferred and non-preferred arms are specialized for different aspects of movement. A recent study by Goble et al. (2006) found evidence of a non-preferred left arm (and presumably right hemisphere) proprioceptive dominance for a target matching task that required subjects to both memorize and transfer across hemispheres proprioceptive target information. This paradigm contrasted previous studies of proprioceptive matching asymmetry that explored only memory-based matching and produced equivocal results. The purpose of the present study, therefore, was to examine task-dependent asymmetries in proprioceptive matching performance, including differences related to active versus passive presentation of the matching target. It was found that the non-preferred left arm of right handers matched target elbow angles more accurately than the preferred arm, but only in the matching condition that required both memory and interhemispheric transfer. Task-dependent asymmetries were not affected by the mode of target presentation and assessment of matching kinematics revealed differences in strategy for both the speed and smoothness of targeted movements. Taken together, these results suggest that the non-preferred arm/hemisphere system is specialized for the processing of movement-related proprioceptive feedback.

Perception of heaviness in Parkinson's disease

The present study investigated whether a specific aspect of proprioception, the sense of heaviness or weight is affected in PD. We determined detection thresholds for the perception of a gravito-inertial load in 10 PD patients and 11 age-matched control subjects. A gradually increasing weight was applied to the index finger by means of two slings of different width (low vs. high skin pressure). For the controls, mean detection thresholds were 31.3 g at skin high pressure and 33.0 g under low pressure. PD patients revealed significantly higher thresholds than the control group in both pressure conditions (mean high pressure,47.7 g; mean low pressure, 52.3 g; group effect, P = 0.001). Thresholds of PD patients tended to increase with disease severity as measured by the Unified Parkinson's Disease Rating Scale Motor score (r = 0.55) but did not correlate significantly with levodopa equivalent dosage. The results demonstrate that the perception of heaviness or weight is already affected in the early stages of PD. These findings underline the growing evidence that proprioceptive and possibly haptic dysfunction is a common feature of PD.

Effect of step-synchronized vibration stimulation of soles on gait in Parkinson's disease: a pilot study

BACKGROUND

Previous studies have suggested that impaired proprioceptive processing in the striatum may contribute to abnormal gait in Parkinson's disease (PD).

METHODS

This pilot study assessed the effects of enhanced proprioceptive feedback using step-synchronized vibration stimulation of the soles (S-VS) on gait in PD. S-VS was used in 8 PD subjects (3 women and 5 men, age range 44-79 years, on medication) and 8 age-matched healthy subjects (5 women and 3 men). PD subjects had mild or moderate gait impairment associated with abnormal balance, but they did not have gait freezing. Three vibratory devices (VDs) were embedded in elastic insoles (one below the heel and two below the forefoot areas) inserted into the shoes. Each VD operates independently and has a pressure switch that activates the underlying vibratory actuator. The VD delivered the 70-Hz suprathreshold vibration pulse upon touch by the heel or forefoot, and the vibration pulse was deactivated upon respective push-offs. Six-minute hallway walking was studied with and without S-VS. Gait characteristics were measured using the force-sensitive foot switches. The primary outcome was the stride variability expressed as a coefficient of variation (CV), a measure of gait steadiness. Secondary outcome measures were walking distance and speed, stride length and duration, cadence, stance, swing and double support duration, and respective CVs (if applicable).

RESULTS

The walking speed (p < 0.04) and the CV of the stride interval (p < 0.02) differed between the groups and S-VS conditions. In the PD group, S-VS decreased stride variability (p < 0.002), increased walking speed (p < 0.0001), stride duration (p < 0.01), stride length (p < 0.0002), and cadence (p < 0.03). In the control group, S-VS decreased stride variability (p < 0.006) and increased gait speed (p < 0.03), but other locomotion parameters were not significantly altered.

CONCLUSION

Augmented sensory feedback improves parkinsonian gait steadiness in the short-term setting. Because the suprathreshold stimulation prevented blinding of subjects, the learning effect and increased attention can be a confounding factor underlying results. Long-term studies are needed to establish the clinical value of the S-VS.

Kinesthesia is impaired in focal dystonia

Parkinson's disease (PD) and focal dystonia (FD) are both predominantly characterized by motor symptoms. Also, recent research has shown that sensory processing is impaired in both movement disorders. FD is characterized by involuntary movements and abnormal limb postures; thus, abnormal kinesthesia could be involved in the pathogenesis. We examined passive index finger movements in patients with FD (n = 12) and PD (n = 11) and in age-matched healthy controls (n = 13). Compared to healthy controls, patients with PD and FD were significantly impaired in the correct detection of the movement direction. The perceptual thresholds for 75% correct responses of movement direction were 0.21 degrees for FD and 0.28 degrees for PD patients compared to 0.13 degrees in control subjects. Subjects with PD and FD were also significantly impaired when they had to judge consecutive amplitudes. Results of the present study point to impaired kinesthesia in FD. Defective sensory processing could be involved in the pathophysiology of the disease and may influence dystonic contractions.

Dysfunction of the basal ganglia, but not the cerebellum, impairs kinaesthesia

Precise knowledge about limb position and orientation is essential for the ability of the nervous system to plan and control voluntary movement. While it is well established that proprioceptive signals from peripheral receptors are necessary for sensing limb position and motion, it is less clear which supraspinal structures mediate the signals that ultimately lead to the conscious awareness of limb position (kinaesthesia). Recent functional imaging studies have revealed that the cerebellum, but not the basal ganglia, are involved in sensory processing of proprioceptive information induced by passive and active movements. Yet psychophysical studies have suggested a prominent role of the basal ganglia in kinaesthesia. This study addresses this apparent dichotomy by investigating the contributions of the cerebellum and the basal ganglia to the perception of limb position. Using a passive movement task, we examined the elbow position sense in patients with a dysfunction of the basal ganglia (Parkinson's disease, n = 9), patients with cerebellar degeneration [spinocerebellar ataxia (SCA) types 6 and 8, n = 6] and age-matched healthy control subjects (n = 11). In comparison with healthy control subjects, Parkinson's disease patients, but not SCA patients, were significantly impaired in the ability to detect displacements correctly. A 1 degrees forearm displacement was correctly recognized in >75% of trials by control subjects and SCA patients, but only in 55% of Parkinson's disease patients. Only at 6 degrees displacement did Parkinson's disease patients exhibit a response rate similar to those of the two other groups. Thresholds for 75% correct responses were 1.03 degrees for controls, 1.15 degrees for cerebellar patients and 2.10 degrees for Parkinson's disease patients. This kinaesthetic impairment significantly correlated with the severity of disease in Parkinson's disease patients, as determined by the Unified Parkinson's Disease Rating Scale (r = -0.7, P = 0.03) and duration of disease (r = -0.7, P = 0.05). In contrast, there was no significant correlation between performance and the daily levodopa equivalent dose. These results imply that an intact cerebro-basal ganglia loop is essential for awareness of limb position and suggest a selective role of the basal ganglia but not the cerebellum in kinaesthesia.