Proprioceptive Perception Research Articles

PDX1, a transcription factor essential for organ differentiation, regulates SERCA-dependent Ca2+ homeostasis in sensory neurons

Pancreatic and duodenal homeobox 1 (PDX1) is a transcription factor required for the development and differentiation of the pancreas. Previous studies indicated that PDX1 expression was restricted to the gastrointestinal tract. Using a cre-dependent reporter, we observed PDX1-dependent expression of tdtomato (PDX1-tom) in a subpopulation of sensory nerves. Many of these PDX1-tom afferents expressed the neurofilament 200 protein and projected to the skin. Tdtomato-labeled terminals were associated with hair follicles in the form of longitudinal and circumferential lanceolate endings suggesting a role in tactile and proprioceptive perception. To begin to examine the functional significance of PDX1 in afferents, we used Fura-2 imaging to examine calcium (Ca2+) handling under naïve and nerve injury conditions. Neuropathic injury is associated with increased intracellular Ca2+ signaling that in part results from dysregulation of the sarco/endoplasmic reticulum calcium transport ATPase (SERCA). Here we demonstrate that under naïve conditions, PDX1 regulates expression of the SERCA2B isoform in sensory neurons. In response to infraorbital nerve injury, a significant reduction of PDX1 and SERCA2B expression and dysregulation of Ca2+ handling occurs in PDX1-tom trigeminal ganglia neurons. The identification of PDX1 expression in the somatosensory system and its regulation of SERCA2B and Ca2+ handling provide a new mechanism to explain pathological changes in primary afferents that may contribute to pain associated with nerve injury.

Soft Polymer Optical Fiber Sensors for Intelligent Recognition of Elastomer Deformations and Wearable Applications.

In recent years, soft robotic sensors have rapidly advanced to endow robots with the ability to interact with the external environment. Here, we propose a polymer optical fiber (POF) sensor with sensitive and stable detection performance for strain, bending, twisting, and pressing. Thus, we can map the real-time output light intensity of POF sensors to the spatial morphology of the elastomer. By leveraging the intrinsic correlations of neighboring sensors and machine learning algorithms, we realize the spatially resolved detection of the pressing and multi-dimensional deformation of elastomers. Specifically, the developed intelligent sensing system can effectively recognize the two-dimensional indentation position with a prediction accuracy as large as ~99.17%. The average prediction accuracy of combined strain and twist is ~98.4% using the random forest algorithm. In addition, we demonstrate an integrated intelligent glove for the recognition of hand gestures with a high recognition accuracy of 99.38%. Our work holds promise for applications in soft robots for interactive tasks in complex environments, providing robots with multidimensional proprioceptive perception. And it also can be applied in smart wearable sensing, human prosthetics, and human-machine interaction interfaces.

Evaluation of vestibular functions in patients with obstructive sleep apnea syndrome

Background To determine the anatomical proximity of the vestibular nuclei to the respiratory nuclei and the effect of susceptibility of the posterior labyrinth to a hypoxic state on the vestibular system. Objective It was aimed to evaluate the possible effects of periodic hypoxia on vestibular reflexes and proprioceptive perception in patients with obstructive sleep apnea syndrome (OSAS). Material and methods The study was conducted with 40 patients diagnosed with moderate and severe OSAS and 21 healthy individuals. All individuals were evaluated with Dizziness Handicap Inventory, ocular vestibular evoked myogenic potential (oVEMP), cervical vestibular evoked myogenic potential (cVEMP), video head impulse test (vHIT), videonystagmography (VNG) and sportKAT 3000. Results In the vHIT, a statistically significant difference was found between the groups in terms of anterior and posterior semicircular canal vestibulo-ocular reflex gains (p < .05). A negative correlation was found between the lateral gain asymmetry and RALP gain asymmetry and the awake blood oxygen level in the OSAS groups. There was a statistically significant difference between the groups in terms of wave response rates cVEMP 100 dB nHL and oVEMP 100–110 dB nHL (p < .05). Conclusion and Significance It was concluded that vestibular reflexes and proprioceptive perception were affected due to periodic/chronic hypoxia in patients with moderate and severe OSAS.

The impact of quadriceps’ fatigue on the proprioceptive perception of the knee joint position sense

The impact of quadriceps’ fatigue on the proprioceptive perception of the knee joint position sense

Method of Objective Assessment of Proprioceptive Perception of Lower Leg and Foot Movements in Human

Method of Objective Assessment of Proprioceptive Perception of Lower Leg and Foot Movements in Human

Method of Objective Assessment of Proprioceptive Perception of Leg and Foot Movements in Humans

Previously, we developed a method for objective assessment of the state of proprioceptive perception of movements of the upper limb. In order to test this method for assessing the proprioceptive perception of lower limb movements, we studied the accuracy of copying with open and closed eyes a series of passive single-joint movements of the tested leg directly during their execution with the help of active movements of the other leg. Flexion-extension copying in the knee and ankle joints was studied in 30 healthy subjects for both legs and in 40 patients with unilateral stroke for the paretic leg. The accuracy of copying movements was assessed by recording the angles in the tested joint and the joint of the same name of the opposite limb using qualitative and quantitative objective indicators. It was shown that healthy subjects, both under visual control and without it, copy the passive movements of the right and left legs with high accuracy and almost simultaneously. Based on the study of the values of qualitative and quantitative indicators of copying accuracy, an objective conditional criterion for the preservation of proprioceptive perception of movements in the knee and ankle joints was formulated. In contrast to healthy subjects, in the group of patients, the results of copying with open and closed eyes were significantly different. In tests with open eyes, the copying of movements was qualitatively correct, which indicates that they understood the motor task of the test and were able to perform it with a conditionally healthy leg. In the absence of visual control, most of them either made gross errors in the transmission of the direction and number of the tested movements, or reproduced movements with a significant deterioration in accuracy (increased delays, shape distortion, etc.). It was shown that the proprioceptive perception of movements in the ankle joint was disturbed more often and more strongly than movements in the knee joint. In accordance with the developed conditional criterion of the norm, in 69% of patients there was a violation of the proprioceptive perception of movements in the knee and/or ankle joints.

Does visual experience influence arm proprioception and its lateralization? Evidence from passive matching performance in congenitally-blind and sighted adults

In humans, body segments’ position and movement can be estimated from multiple senses such as vision and proprioception. It has been suggested that vision and proprioception can influence each other and that upper-limb proprioception is asymmetrical, with proprioception of the non-dominant arm being more accurate and/or precise than proprioception of the dominant arm. However, the mechanisms underlying the lateralization of proprioceptive perception are not yet understood. Here we tested the hypothesis that early visual experience influences the lateralization of arm proprioceptive perception by comparing 8 congenitally-blind and 8 matched, sighted right-handed adults. Their proprioceptive perception was assessed at the elbow and wrist joints of both arms using an ipsilateral passive matching task. Results support and extend the view that proprioceptive precision is better at the non-dominant arm for blindfolded sighted individuals. While this finding was rather systematic across sighted individuals, proprioceptive precision of congenitally-blind individuals was not lateralized as systematically, suggesting that lack of visual experience during ontogenesis influences the lateralization of arm proprioception.

The effect of mirror therapy on joint movement, pain and functionality in acute upper limb burns

ObjectiveMirror therapy is aimed at developing a normal proprioceptive perception for the area with pain or movement restriction by making use of the person's monitoring of the healthy side movements thanks to the mirror's reflective feature. The aim of this study is to investigate the effect of mirror therapy on joint range of motion, pain and functionality in acute upper extremity burn injuries. MethodsDemographic and burn-specific data of individuals with upper extremity burns were recorded. Individuals were divided into two groups. Standard treatment was applied to the first group, and mirror treatment in addition to the standard treatment was applied to the second group for 30 sessions, 5 days a week for 6 weeks. In the standard treatment program, passive, active-assisted and active ROM, strengthening, stretching, resistant and functional exercises were applied. In the mirror therapy group, active exercises were performed on the healthy side by covering the burn area in the mirror box. Before and after the treatment, joint range of motion(ROM) was evaluated with Universal Goniometer, pain intensity was evaluated with Visual Analog Scale and upper extremity functions were evaluated with QuickDASH. ResultsA total of 32 (23 Male, 9 Female) individuals between the ages of 18–65 were included. The mean total burn surface area was 12.93 ± 9.80 in the standard treatment and 6.12 ± 2.96 in the mirror treatment. The groups were similar in terms of ROM change (p > 0.05). The pretest/posttest pain scores of both the standard therapy and mirror therapy groups were similar (p > 0.05). There was no statistically significant difference in terms of pretest and posttest QuickDASH scores according to the groups (p > 0.05). The difference between the pretest/posttest QuickDASH scores of both Standard treatment and Mirror treatment groups was statistically significant. ConclusionThis study showed that the standard physiotherapy and rehabilitation program applied in the acute period in upper extremity burns and the mirror treatment applied in addition to this program provide similar improvements in joint range of motion and pain.

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.

Proprioceptive perception of the ankle joint is impaired in developmental coordination disorder

Transcranial direct current stimulation (tDCS) can polarize the cortex of the human brain.We sought to verify the hypothesis that posterior-anterior (PA) but not anterior-posterior (AP) tDCS of primary motor cortex (M1) produces cooperative effects with corticospinal plasticity induced by paired associative stimulation of the supplementary motor area (SMA) to M1 projection (PASSMA→M1) in a highly controlled experimental design.Three experimental conditions were tested in a double-blinded, randomized crossover design in 15 healthy adults: Navigated PASSMA→M1 during PA-tDCS (35 cm2 electrodes, anode 3 cm posterior to M1 hand area, cathode over contralateral frontopolar cortex, 1 mA, 2 × 5 min) or AP-tDCS (reversed polarity), or sham-tDCS. Effects were analyzed over 120 min post-intervention by changes of motor evoked potential (MEP) amplitude in a hand muscle.There was no significant effect of tDCS on PASSMA→M1 induced plasticity in the repeated-measures ANOVA. However, post-hoc within-subject contrasts revealed a significant tDCS with PASSMA→M1 interaction. This was explained by PA-tDCS and AP-tDCS modifying the PASSMA→M1 effect into the same direction in 13/15 subjects (87%, p = 0.004 for deviation from equality). Sizes of the PA-tDCS and AP-tDCS effects were correlated (rs = 0.53, p = 0.044). A control experiment demonstrated that PA-tDCS and AP-tDCS alone (without PASSMA→M1) had no effect on MEP amplitude.Data point to unidirectional tDCS effects on PASSMA→M1 induced plasticity irrespective of tDCS polarity, in contrast to our hypothesis. We propose that radial symmetry of cortical columns, gyral geometry of motor cortex, and cooperativity of plasticity induction can explain the findings.

Virtual Reality-Induced Sensorimotor Conflict Evokes Limb-Specific Sensory Disturbances in Complex Regional Pain Syndrome

The origin of sensory disturbances in complex regional pain syndrome (CRPS) remains unclear. It has been hypothesized that such disturbances are due to attentional effects and/or sensorimotor integration deficits. If sensory disturbances are explained by sensorimotor integration deficits, they would be expected to be specific in terms of the category of sensation evoked and in terms of localization. Objective 1: To test whether sensory disturbances evoked by a unilateral sensorimotor conflict are specific to the painful limb and differ according to the category of sensory disturbances in individuals with a unilateral CRPS compared to healthy controls (HC). Objective 2: To assess the association between clinical characteristics and conflict-induced sensory disturbances. Objective 3: To assess conflict-induced motor disturbances. Ten adults with upper limb (UL) CRPS and 23 HC were recruited. Sensorimotor conflict was elicited with a KINARM exoskeleton interfaced with a 2D virtual environment allowing the projection of a virtual UL that was moving in either a congruent or incongruent manner relative to the actual UL movement. Participants rated sensory disturbances from 0 (no change) to 3 (high change) on a 8-item questionnaire. Items were classified into two Categories (Category 1: pain, discomfort, the feeling of losing a limb, change in weight and temperature; Category 2: feelings of peculiarity, the impression of gaining a limb and losing control). Motor disturbances were quantified as mediolateral drift and changes in amplitude of UL movement. Clinical characteristics included the intensity and duration of pain, proprioception, and body perception. CRPS participants report higher Category 1 than Category 2 disturbances for the Affected limb (while the reverse was observed for HC and for the Unaffected limb). In addition, no difference was observed between the Unaffected limb in CRPS and the Dominant limb in HC for Category 2 disturbances, while higher conflict sensitivity was observed for Category 1 disturbances. Conflict sensitivity was only related to higher pain for Category 1 disturbances in the Affected limb. Finally, no effect on motor disturbances was observed. While they do not completely rule out the attentional hypothesis, these results support the hypothesis of sensorimotor integration deficits.

Proprioceptive Stimulation Added to a Walking Self-Avatar Enhances the Illusory Perception of Walking in Static Participants

When immersed in virtual reality, users who view their body as a co-located virtual avatar that reflects their movements, generally develop a sense of embodiment whereby they perceive the virtual body to be their own. One aspect of the sense of embodiment is the feeling of agency over the avatar, i.e., the feeling that one is producing the movements of the avatar. In contexts such as physical rehabilitation, telepresence and gaming, it may be useful to induce a strong sense of agency in users who cannot produce movements or for whom it is not practical to do so. Being able to feel agency over a walking avatar without having to produce walking movements could be especially valuable. Muscle vibrations have been shown to produce the proprioceptive perception of movements, without any movement on the part of the user. The objectives of the current study were to: 1-determine if the addition of lower-limb muscle-vibrations with gait-like patterns to a walking avatar can increase the illusory perception of walking in healthy individuals who are standing still; 2-compare the effects of the complexity of the vibration patterns and of their synchronicity on the sense of agency and on the illusory perception of walking. Thirty participants viewed a walking avatar from a first-person perspective, either without muscle vibrations or with one of four different patterns of vibrations. These five conditions were presented pairwise in a two-alternative forced choice paradigm and individually presented, after which participants answered an embodiment questionnaire. The displacement of center of pressure of the participants was measured throughout the experiment. The results show that all patterns of proprioceptive stimulation increased the sense of agency to a similar degree. However, the condition in which the proprioceptive feedback was realistic and temporally aligned with the avatar’s leg movements led to significantly larger anteroposterior sway of the center of pressure. The frequency of this sway matched the cadence of the avatar’s gait. Thus, congruent and realistic proprioceptive stimulation increases the feeling of agency, the illusory perception of walking and the motor responses of the participants when viewing a walking avatar from a first-person perspective.

3D Quantitative Evaluation of Posture and Spine Proprioceptive Perception Through Instinctive Self-Correction Maneuver in Adolescent Idiopathic Scoliosis.

BackgroundConservative treatment in the adolescent idiopathic scoliosis (AIS) population is based on individual proprioceptive and motor control training. Such training includes physiotherapeutic scoliosis-specific exercises (PSSEs) stimulating the individual capacity to perceive and control his/her posture, particularly the shape of the spine. However, limited knowledge about basic proprioception capability in AIS patients is reported in the literature.Questions(1) How do AIS patients, who did not receive any previous specific postural education treatment, perceive their posture and 3D spine shape? Are they able to modify their posture and 3D spine shape correctly through an instinctive self-correction (ISCO) maneuver? (2) Are posture and ISCO maneuver ability gender dependent in AIS patients? (3) Do AIS patients present different posture and spine shape characteristics as well as different ISCO ability compared with the healthy young adult population?MethodsCross-sectional observational study. 132 (75 females, 57 males) AIS patients’ posture and 3D spine shape have been measured comparing indifferent orthostasis (IO) (neutral erect posture) to ISCO using a non-ionizing 3D optoelectronic stereophotogrammetric approach. Thirteen quantitative biomechanical parameters described the AIS patients body posture. The statistical analysis was performed using a multivariate approach to compare genders in IO, ISCO, and AIS patients vs. healthy young adults–previously published data (57 females, 64 males).ResultsMales (87.7%) and females (93.3%) of AIS patients were unable to modify posture and 3D spine shape globally. AIS patients gender differences were found in IO, ISCO, and the comparison vs. healthy young adults. When changes occurred, subjects could not focus and control their posture globally, but only in a few aspects at a time.ConclusionSelf-correction maneuver producing an improvement in body posture and spine shape is not instinctive and must be trained. In such characteristics, AIS patients are not so dissimilar to healthy young adults. Sagittal plane control is the highest, but ISCO in AIS patients led to worsening in this plane. Control at the lumbar level is neglected in both genders. Such outcomes support the necessity of customized PSSEs to treat AIS patients. The 3D stereo-photogrammetric approach is effective in quantitatively describing the subject’s posture, motor control, and proprioception.

Objective Evaluation of Proprioceptive Perception of Single-Joint Arm Movements in Patients with Hemiparesis of Central Genesis

Aim. Objective evaluation of proprioceptive perception of single-joint movements of the paretic arm in patients with unilateral brain damage using the method developed by us. Materials and Methods. Proprioceptive perception of pronation-supination of the forearm, flexion-extension in the shoulder, elbow and wrist joints and abduction-adduction in the shoulder and wrist joints was tested in 23 patients with right-sided and 17 patients with left-sided brain damage. The subject with his eyes closed was made to perform a series of passive cyclical test movements, during which he had to copy them with active movements of the other arm. Joint angles were recorded in the test joint and the same joint ofthe other arm. The integrity of proprioceptive sensitivity was judged by the degree of similarity between “active” and “passive” movements estimated by means of objective qualitative and quantitative indicators. Results. Proprioceptive deficiency was detected in 83% of patients with lesion in the right and in 71% of patients with lesion inthe left hemisphere, while the proportion of test movements that revealed a violation of proprioceptive perception was 1.4 times higher in the right-hemisphere patients than in the left-hemisphere patients. A significant part of proprioceptive impairments, – 80% when testing movements of more distal and 29% – proximal segments of the arm, was detected by the presence of qualitative copying errors. Conclusions. The method used made it possible to identify proprioceptive deficits in more than half of patients with damage to both the right and left hemispheres. Proprioceptive perception of movements of the distal arm segment suffered more often and was more pronounced than the proximal one. A significant part of distal segment proprioception disorders manifested themselves in the form of gross qualitative copying errors, which can be detected visually during testing, even without the use of recording equipment.

Investigation of the effect of sensorimotor exercises on proprioceptive perceptions among children with spastic hemiplegic cerebral palsy

Study DesignThis is a blinded randomized clinical trial. IntroductionSensorimotor exercises may be an effective, noninvasive treatment modality for treating patients with pediatric spastic hemiplegic cerebral palsy (CP). Purpose of the StudyWe aim to evaluate the effect of sensorimotor exercises on the proprioceptive capability among children with spastic hemiplegic CP. MethodsThis randomized clinical trial was performed on children with spastic hemiplegic CP. Thirty children aged 8 to 12 years old, with spastic hemiplegic CP, were randomly selected and equally divided into experimental and control groups (N = 15 for each). A joint positioning test was used to measure the patients' baseline proprioceptive ability. The exercise program included sensory and motor exercises which lasted for 8 weeks (three 60-min sessions per week). The data were analyzed by using Welch and paired-sample t-test at the significance level of P < .05. ResultsThe results indicated that the proprioceptive capability of the upper limb could significantly improve (P = .001, effect size = 0.41, observed power = 0.99) by using simultaneous exercising of the sensorimotor complex. The mean increased from 8.53 ± 1.6 to 10.53 ± 1.19 in the experimental group, whereas it changed from 6.66 ± 3.44 to 6.73 ± 3.15 in the control group. DiscussionIn consistent with other studies, the exercises used in the present study enhanced the proprioceptive capability but not sensory performance of the hands of children with hemiplegic. Synchronous sensory and motor training in children with hemiplegic CP may improve the function and organization of the somatosensory cortex and reduce sensory disturbances. Although parents were subjectively satisfied with the outcome of the exercises, such as independency and life style, however these recordings were not measured in this study. ConclusionImplementing simultaneous sensorimotor exercises can improve the proprioceptive capability of the hand. Therefore, these exercises can be used in the rehabilitation programs to meet the children's needs with hemiplegic CP.

Effect of Neck Botulinum Neurotoxin Injection on Proprioception and Somatosensory-Motor Cortical Processing in Cervical Dystonia

Background. Cervical dystonia (CD) is a neurological movement disorder characterized by involuntary contractions of the cervical musculature and is known to be associated with proprioceptive dysfunction in dystonic/nondystonic limbs. Objectives. We examined how neck botulinum neurotoxin (BoNT) injection affects wrist proprioception and the corresponding sensorimotor cortical activity in CD. Method. Wrist position sense acuity of the dominant (right) hand was evaluated in 15 CD and 15 control participants. Acuity measures were a psychophysical position sense discrimination threshold (DT; based on passive joint displacement) and joint position matching error (based on active movement). Cortical activity during the motor preparation period of the active joint position matching was examined using electroencephalography. Results. In their symptomatic state, patients demonstrated a significantly higher wrist proprioceptive DT, indicating an abnormal passive wrist position sense. Yet BoNT injections had no significant effect on this threshold. During active joint position matching, errors were significantly larger in patients, but this difference vanished after the administration of BoNT. Motor preparation of active wrist position matching was associated with a significantly higher rise of β-band (13-30 Hz) power over contralateral somatosensory-motor cortical areas in patients. This excessive cortical activity significantly declined post-BoNT. Conclusion. Wrist proprioceptive perception during passive/active movements is abnormal in CD. An excessive rise of premotor/motor cortical β-oscillations during motor planning is associated with this proprioceptive dysfunction. Neck BoNT injections normalized the cortical processing of proprioceptive information from nonsymptomatic limbs, indicating that local injections may affect the central mechanisms of proprioceptive function in CD.

Altered Visual and Proprioceptive Spatial Perception in Individuals with Parkinson's Disease.

Difficulties in the integration of visual, vestibular, and somatosensory information in individuals with Parkinson's disease (PD) may alter perception of verticality. Accordingly, in this cross-sectional study, we analyzed PD patients' (n = 13) subjective visual vertical (SVV) and subjective haptic vertical (SHV) perceptions and compared them to those of healthy controls (n = 14). We compared SVV and SHV findings among participants with PD, healthy controls, and cutoff points of normality based on prior research literature, using the parametric nonpaired t test (at p < .05) and Cohen's d (at d > 0.8) to determine clinical relevance. We analyzed SVV with the bucket test and SHV with the rod rotations task in clockwise and counterclockwise directions. We calculated Pearson correlations to analyze the association between verticality tests and the most clinically affected body side. We calculated both the percentage of A-effect (expression of body tilt underestimation to the midline) and E-effect (expression of body tilt overestimation in the upright position). Individuals with PD showed greater variability in right SHV supination compared to the healthy control participants (p = .002). There was greater clinical relevance in right (as opposed to left) SVV (d = 0.83), right (as opposed to left) SHV pronation (d = 0.91), and left (as opposed to right) SHV pronation (d = 0.88). We observed a higher proportion of E-effect in individuals with PD. A significantly higher proportion of patients with PD, compared to patients in past literature, had right SHV pronation (p = .001), left SHV pronation (p = .023), right SHV supination (p = .001), left SHV supination (p = .046), and left SHV pronation (p = .046). Thus, subjective visual and proprioceptive perception of verticality is altered in patients with PD, compared to individuals without PD.

Comparison of Objective Indicators of Proprioception of Single–joint Arm Movements in Healthy Subjects and Post–Stroke Patients in Sitting and Lying Positions

Testing of sensory-motor performance and motor rehabilitation training in post-stroke patients are often executed in lying position. At the same time, influence of the body position on proprioceptive perception is poorly studied. In this study, we have investigated proprioceptive perception of single-joint arm movements in 10 healthy subjects and 17 post-stroke patients with unilateral arm paresis in the sitting and lying positions using the method we developed. Movements of flexion–extension in shoulder, elbow and wrist joints and abduction–adduction in shoulder and wrist joints were tested. The subjects were made to perform a series of the passive single-joint movements with the eyes closed and had to copy these movements simultaneously by active movements of another arm. We recorded the angles at the tested joint and the homonymous joint of the other arm, and the status of proprioceptive sensitivity was evaluated basing on the degree of similarity of these “passive” and “active” movements. Qualitative and quantitative indicators were used to assess the similarity. It was found that healthy subjects reproduce the passive movements without rough qualitative errors in both the sitting and lying positions. The movement reproduction was less accurate in the lying position by values of some quantitative indicators, however only 3% of trails did not match the conventional criterion for proprioceptive sensitivity intactness. On the contrary, the movement reproduction in almost half of tests in the group of post-stroke patients was performed with qualitative and quantitative errors and did not match the requirements of the conventional criterion. A deficit of proprioception was observed in 1 to 5 different test-movements in 88% of patients in the sitting position and 71% of patients in the lying position. Most frequent and rough errors in the movement reproduction were observed in distal segments of the paretic arm. It was found that the body position could have different effects on the proprioceptive perception of the same test-movement in patients: the proprioceptive perception was evaluated as intact in the sitting position and as distorted in the lying position in 14% of all test trials and vice versa it was evaluated as distorted in sitting position and as intact in lying positions in 17% of trials. Such individual differences must be considered when choosing conditions for motor rehabilitation procedures in patients with paresis of the arm.

Somatosensory Loss Influences the Adoption of Self-Centered Versus Decentered Perspectives.

The body and the self are commonly experienced as forming a unity. Experiencing the external world as distinct from the self and the body strongly relies on adopting a single self-centered perspective which results in integrating multisensory sensations into one egocentric body-centered reference frame. Body posture and somatosensory representations have been reported to influence perception and specifically the reference frame relative to which multisensory sensations are coded. In the study reported here, we investigated the role of somatosensory and visual information in adopting self-centered and decentered spatial perspectives. Two deafferented patients who have neither tactile nor proprioceptive perception below the head and a group of age-matched control participants performed a graphesthesia task, consisting of the recognition of ambiguous letters (b, d, p, and q) drawn tactilely on head surfaces. To answer which letter was drawn, the participants can adopt either a self-centered perspective or a decentered one (i.e., centered on a body part or on an external location). The participants’ responses can be used, in turn, to infer the way the left-right and top-bottom letters’ axes are assigned with respect to the left-right and top-bottom axes of their body. In order to evaluate the influence of body posture, the ambiguous letters were drawn on the participants’ forehead, left, and right surfaces of the head, with the head aligned or rotated in yaw relative to the trunk. In order to evaluate the role of external information, the participants completed the task with their eyes open in one session and closed in another one. The results obtained in control participants revealed that their preferred perspective varied with body posture but not with vision. Different results were obtained with the deafferented patients who overall do not show any significant effect of their body posture on their preferred perspective. This result suggests that the orientation of their self is not influenced by their physical body. There was an effect of vision for only one of the two patients. The deafferented patients rely on strategies that are more prone to interindividual differences, which highlights the crucial role of somatosensory information in adopting self-centered spatial perspectives.

Somatosensory perceptual training enhances motor learning by observing.

Action observation activates brain regions involved in sensory-motor control. Recent research has shown that action observation can also facilitate motor learning; observing a tutor undergoing motor learning results in functional plasticity within the motor system and gains in subsequent motor performance. However, the effects of observing motor learning extend beyond the motor domain. Converging evidence suggests that observation also results in somatosensory functional plasticity and somatosensory perceptual changes. This work has raised the possibility that the somatosensory system is also involved in motor learning that results from observation. Here we tested this hypothesis using a somatosensory perceptual training paradigm. If the somatosensory system is indeed involved in motor learning by observing, then improving subjects' somatosensory function before observation should enhance subsequent motor learning by observing. Subjects performed a proprioceptive discrimination task in which a robotic manipulandum moved the arm, and subjects made judgments about the position of their hand. Subjects in a Trained Learning group received trial-by-trial feedback to improve their proprioceptive perception. Subjects in an Untrained Learning group performed the same task without feedback. All subjects then observed a learning video showing a tutor adapting her reaches to a left force field. Subjects in the Trained Learning group, who had superior proprioceptive acuity before observation, benefited more from observing learning than subjects in the Untrained Learning group. Improving somatosensory function can therefore enhance subsequent observation-related gains in motor learning. This study provides further evidence in favor of the involvement of the somatosensory system in motor learning by observing. NEW & NOTEWORTHY We show that improving somatosensory performance before observation can improve the extent to which subjects learn from watching others. Somatosensory perceptual training may prime the sensory-motor system, thereby facilitating subsequent observational learning. The findings of this study suggest that the somatosensory system supports motor learning by observing. This finding may be useful if observation is incorporated as part of therapies for diseases affecting movement, such as stroke.