Does proprioception contribute to the sense of verticality?

Fear of heights shapes postural responses to vibration-induced balance perturbation at virtual height

Introduction

Standing upright at height is a challenging situation involving intense threat of balance loss and fall. The ability to maintain balance in such conditions requires properly resolving sensory conflicts and is influenced by fear. To get more insight on the role of fear in balance control at height, we explored the dynamics of postural behavior in the situation of enhanced threat of potential balance loss.

Methods

In 40 young individuals with varying fear of heights, we combined simulated exposure to height in a virtual reality environment with bilateral vibration of tibialis anterior muscles which evokes posture destabilization (the so-called vibration-induced falling).

Results

Under such condition of enhanced postural threat, individuals with intense fear of heights showed stronger stiffening of posture compared with individuals with low fear of heights who react more flexibly and adaptively to posture destabilization. This group difference was evident already at ground level but further increased during virtual height exposure.

Discussion

Our data show that fear of height significantly affects posture adaptation to balance-destabilizing events. Our findings demonstrate that the assessment of postural behavior during threatening situations in the virtual reality environment provides valuable insights into the mechanisms of balance control and may be used to develop novel strategies aimed at prevention of falls.

Biological Responses to Local Vibratory Stimulation for the Lower Legs and Lower Back and Criterion Values Based on Sweep Frequencies of Healthy Individuals: An Observational Study

Declining proprioceptive function is associated with problems such as lower back pain and falls. Therefore, we developed a vibration device using sweep frequency to evaluate several proprioceptors with different response frequency ranges. This study aimed to elucidate the biological responses of healthy individuals to vibratory stimulation at different sites and frequency ranges and to propose cutoff values to determine the decline in proprioceptive function. Mechanical vibration was separately applied to the lower legs and lower back, and proprioceptive function was evaluated by defining the ratio of the center of pressure (CoP) in the anteroposterior direction during mechanical vibration to that during no vibration in the three frequency ranges. The cut-off value was defined as the mean value, with the standard deviation subtracted for each indicator. The cut-off values were higher in the lower legs than in the lower back at all frequency ranges and in the 30-53 Hz and 56-100 Hz frequency ranges for both the lower legs and lower back. In healthy individuals, 9.9% and 8.6% were below the cut-off values in the 30-53 Hz and 56-100 Hz frequency ranges for the lower legs, respectively.

Effectiveness and safety of subthreshold vibration over suprathreshold vibration in treatment of muscle fatigue in elderly people

Muscle fatigue is common in many populations, particularly elderlies. Aging increases the incidence of muscle fatigue and delays its recovery. There is a huge debate about the current treatments for muscle fatigue, particularly in elderlies. Recently, it has been discovered that mechanoreceptors have an important role as a sensory system in sensing muscle fatigue which could enhance the body's response to muscle fatigue. The function of mechanoreceptors could be enhanced by applying either suprathreshold or subthreshold vibration. Although suprathreshold vibration improves muscle fatigue, it can cause desensitization of cutaneous receptors, discomfort, and paresthesia, which are barriers to clinical use. Subthreshold vibration has been approved as a safe and effective method of training for mechanoreceptors; however, its use and effectiveness in muscle fatigue have never been tested or explained. Possible physiological effects of subthreshold vibration in the treatment of muscle fatigue include: (1) Enhancing the function of mechanoreceptors themselves; (2) Increasing the firing rate and function of alpha motor neurons; (3) Increasing blood flow to fatigued muscles; (4) Decreasing the rate of muscle cell death in elderlies (sarcopenia); and (5) Driving motor commands and allow better performance of muscles to decrease fatigue incidence. In conclusion, the use of subthreshold vibration could be a safe and effective treatment for muscle fatigue in elderlies. It could enhance recovery from muscle fatigue. Finally, Subthreshold Vibration is safe and effective in treating muscle fatigue in comparison to suprathreshold vibration.

The effects of proprioceptive weighting changes on posture control in patients with chronic low back pain: a cross-sectional study

Introduction

Patients with chronic low back pain (CLBP) exhibit changes in proprioceptive weighting and impaired postural control. This study aimed to investigate proprioceptive weighting changes in patients with CLBP and their influence on posture control.

Methods

Sixteen patients with CLBP and 16 healthy controls were recruited. All participants completed the joint reposition test sense (JRS) and threshold to detect passive motion test (TTDPM). The absolute errors (AE) of the reposition and perception angles were recorded. Proprioceptive postural control was tested by applying vibrations to the triceps surae or lumbar paravertebral muscles while standing on a stable or unstable force plate. Sway length and sway velocity along the anteroposterior (AP) and mediolateral (ML) directions were assessed. Relative proprioceptive weighting (RPW) was used to evaluate the proprioception reweighting ability. Higher values indicated increased reliance on calf proprioception.

Results

There was no significant difference in age, gender, and BMI between subjects with and without CLBP. The AE and motion perception angle in the CLBP group were significantly higher than those in the control group (JRS of 15°: 2.50 (2.50) vs. 1.50 (1.42), JRS of 35°: 3.83 (3.75) vs. 1.67 (2.00), p_JRS < 0.01; 1.92 (1.18) vs. 0.68 (0.52), p_TTDPM < 0.001). The CLBP group demonstrated a significantly higher RPW value than the healthy controls on an unstable surface (0.58 ± 0.21 vs. 0.41 ± 0.26, p < 0.05). Under the condition of triceps surae vibration, the sway length (p_stable < 0.05; p_unstable < 0.001), AP velocity (p_stable < 0.01; p_unstable < 0.001) and ML velocity (p_unstable < 0.05) had significant group main effects. Moreover, when the triceps surae vibrated under the unstable surface, the differences during vibration and post vibration in sway length and AP velocity between the groups were significantly higher in the CLBP group than in the healthy group (p < 0.05). However, under the condition of lumbar paravertebral muscle vibration, no significant group main effect was observed.

Conclusion

The patients with CLBP exhibited impaired dynamic postural control in response to disturbances, potentially linked to changes in proprioceptive weighting.

Spatial neglect encompasses impaired verticality representation after right hemisphere stroke

Spatial neglect after right hemisphere stroke (RHS) was recently found to encompass lateropulsion, a deficit in body orientation with respect to gravity caused by altered brain processing of graviception. By analogy, we hypothesized that spatial neglect after RHS might encompass an altered representation of verticality. We also assumed a strong relation between body neglect and impaired postural vertical, both referring to the body. To tackle these issues, we performed contingency and correlation analyses between two domains of spatial neglect (body, extra-body) and two modalities of verticality perception (postural, visual) in 77 individuals (median age = 67) with a first-ever subacute RHS (1-3 months). All individuals with a transmodal (postural and visual) tilt in verticality perception (n = 26) had spatial neglect, but the reverse was not found. Correlation and multivariate analyses revealed that spatial neglect (and notably body neglect) was associated more with postural than visual vertical tilts. These findings indicate that after RHS, an impaired verticality representation results from a kind of graviceptive neglect, bearing first on somaesthetic graviception and second on vestibular graviception. They also suggest that the human brain uses not only a mosaic of 2D representations but also 3D maps involving a transmodal representation of verticality.

3D Stereophotogrammetric Quantitative Evaluation of Posture and Spine Proprioception in Subacute and Chronic Nonspecific Low Back Pain

The literature shows that low back pain causes a reduced lumbar range of movement, affecting patients’ proprioception and motor control. Nevertheless, studies have found that proprioception and motor control of the spine and posture are vague and individually expressed even in healthy young adults. This study aimed to investigate the standing posture and its modifications induced by an instinctive self-correction manoeuvre in subacute and chronic nonspecific low back pain (NSLBP) patients to clarify how NSLBP relates to body upright posture, proprioception, and motor control and how these are modified in patients compared to healthy young adults (121 healthy young adults: 57 females and 64 males). A cohort of 83 NSLBP patients (43 females, 40 males) were recruited in a cross-sectional observational study. Patients’ entire body posture, including 3D spine shape reconstruction, was measured using a non-ionising 3D optoelectronic stereophotogrammetric approach. Thirteen quantitative biomechanical parameters describing the nature of body posture were computed. The statistical analysis was performed using multivariate methods. NSLBP patients did not present an altered proprioception and motor control ability compared to healthy young adults. Furthermore, as for healthy subjects, NSLBP patients could not focus and control their posture globally. Proprioception and motor control in natural erect standing are vague for most people regardless of gender and concurrent nonspecific low back pain. Self-correction manoeuvres improving body posture and spine shape must be learned with specific postural training focusing on the lumbar spine.

Preceding Postural Control in Forelimb Reaching Movements in Cats

Postural control precedes the goal-directed movement to maintain body equilibrium during the action. Because the environment continuously changes due to one’s activity, postural control requires a higher-order brain function that predicts the interaction between the body and the environment. Here, we tried to elucidate to what extent such a preceding postural control (PPC) predictively offered a posture that ensured the entire process of the goal-directed movement before starting the action. For this purpose, we employed three cats, which we trained to maintain a four-leg standing posture on force transducers to reach the target by either forelimb. Each cat performed the task under nine target locations in front with different directions and distances. As an index of posture, we employed the center of pressure (CVP) and examined CVP positions when the cat started postural alteration, began to lift its paw, and reached the target. After gazing at the target, each cat started PPC where postural alteration was accompanied by a 20–35 mm CVP shift to the opposite side of the forelimb to be lifted. Then, the cat lifted its paw at the predicted CVP position and reached the forelimb to the target with a CVP shift of only several mm. Moreover, each cat had an optimal target location where the relationship between the cat and target minimized the difference in the CVP positions between the predicted and the final. In this condition, more than 80% of the predicted CVP positions matched the final CVP positions, and the time requiring the reaching movement was the shortest. By contrast, the forelimb reaching movement required a greater CVP shift and longer time when the target was far from the cat. In addition, the time during forelimb reaching showed a negative correlation with the speed of the CVP shift during the PPC. These results suggest that the visuospatial information, such as the body-environment interaction, contributes to the motor programming of the PPC. We conclude that the PPC ensures postural stability throughout the action to optimize the subsequent goal-directed movements. Impairments in these processes may disturb postural stability during movements, resulting in falling.

Posture dependent ankle and foot muscle responses evoked by Achilles' tendon vibration

To investigate the link between the triceps surae and the intrinsic muscles of the foot, often underestimated in posture maintenance, we asked how Achilles' tendon vibration modulates the EMG activity of the soleus and flexor digitorum brevis (FDB) muscles during different postural tasks: sitting, standing and forward leaning. Young healthy participants (n = 19, age = 24 ± 7.4 years) stood for 60 s in three visually controlled postures, while vibration (1.5-1.8 mm, 80 Hz) was bilaterally applied over the Achilles' tendon during the middle 20 s. Center of Pressure (CoP) and EMG activity of the soleus and FDB muscle were summarized in 5 s epochs and compared across time (before, during and after vibration) and postural tasks. Achilles' tendon vibration shifted the CoP position forward in sitting and backward in standing and leaning and increased the root mean square of the CoP velocity to a greater extent in standing and leaning compared to sitting. Soleus and FDB EMG amplitude also increased in response to vibration. These responses were posture dependent, being greater in standing (soleus: 57 %, FDB: 67 % relative to pre-vibration) compared to sitting (soleus: 36 %, FDB: 27 % relative to pre-vibration) and leaning (soleus: 26 %, FDB: 8% relative to pre-vibration). After vibration offset, both soleus and FDB showed sustained activation across all three postures. Results highlight the presence of Ia afferent projections from the soleus to the α motor neurons of the FDB muscle triggered by Achilles' tendon vibration. This link is posture dependent serving a functional role in standing and forward leaning in the presence of externally applied perturbations.

Visual and haptic verticality misperception and trunk control within 72 h after stroke

INTRODUCTION

Stroke patients often exhibit an altered perception of verticality, but there are no studies evaluating verticality perception in the first 72 h after stroke and its relationship with trunk control. Therefore, this study aimed to analyze visual and haptic verticality in the acute phase of stroke.

METHODS

This was a cross-sectional study conducted with two groups: (a) 13 individuals with stroke and (b) 12 healthy participants. We assessed verticality via the subjective visual vertical (SVV) and the subjective haptic vertical (SHV); and we measured trunk control with the Trunk Impairment Scale (TIS). We performed t-tests to compare the SVV and SHV between groups. Pearson correlation was performed between verticality tests with National Institutes of Health Stroke Scale (NIHSS) and the TIS.

RESULTS

Participants with recent stroke presented higher true and absolute SVV deviation values than did the control group. There was significant negative correlation between absolute (r = -0.57; p = 0.02) and true SVV (r = -0.54; p = 0.01) with TIS scores There was also significant positive correlation between absolute (r = 0.63; p = 0.009) and true SVV (r = 0.61; p = 0.003) with NIHSS. A significant negative correlation between NIHSS and TIS scores also was found (r = -0.80; p = 0.005).

CONCLUSION

Individuals with acute stroke presented larger variability in their perceptions of visual verticality than did healthy controls, and verticality perceptions were positively correlated with trunk impairment.

Distinct adaptation patterns between grip dynamics and arm kinematics when the body is upside-down

In humans, practically all movements are learnt and performed in a constant gravitational field. Yet, studies on arm movements and object manipulation in parabolic flight have highlighted very fast sensorimotor adaptations to altered gravity environments. Here, we wondered if the motor adjustments observed in those altered gravity environments could also be observed on Earth in a situation where the body is upside-down. To address this question, we asked participants to perform rhythmic arm movements in two different body postures (right-side-up and upside-down) while holding an object in precision grip. Analyses of grip-load force coordination and of movement kinematics revealed distinct adaptation patterns between grip and arm control. Grip force and load force were tightly synchronized from the first movements performed in upside-down posture, reflecting a malleable allocentric grip control. In contrast, velocity profiles showed a more progressive adaptation to the upside-down posture and reflected an egocentric planning of arm kinematics. In addition to suggesting distinct mechanisms between grip dynamics and arm kinematics for adaptation to novel contexts, these results also suggest the existence of general mechanisms underlying gravity-dependent motor adaptation that can be used for fast sensorimotor coordination across different postures on Earth and, incidentally, across different gravitational conditions in parabolic flights, in human centrifuges, or in Space.NEW & NOTEWORTHY During rhythmic arm movements performed in an upside-down posture, grip control adapted very quickly, but kinematics adaptation was more progressive. Our results suggest that grip control and movement kinematics planning might operate in different reference frames. Moreover, by comparing our results with previous results from parabolic flight studies, we propose that a common mechanism underlies adaptation to unfamiliar body postures and adaptation to altered gravity.

Comparison of two methods based on one psychophysical paradigm to measure the subjective postural vertical in standing

The perception of verticality can be altered with age or due to neurological diseases. Different procedures have been described to measure the subjective postural vertical (SPV). A deviation from the earth vertical was either described as a single position or as a sector defined by two positions representing the edges of the perceived verticality. In this study, for the first time, we investigated if these two methods produce equal values, and consequently can be merged to set normative values. SPV in standing was tested in 24 healthy young adults (28.4 (5.2) years of age, 12 women). Each participant performed both methods in the sagittal and the frontal plane. Absolute and constant error values were found to be similar for both methods in both planes with a mean difference of less than 0.3° (p > 0.148). The mean width of the SPV sector was 3.9° (0.9°) in the sagittal and 3.7° (1.4°) in the frontal plane, ranging in the mean from -5.5° to 8.1° in the sagittal and -5.3° to 4.3° in the frontal plane. SPV values significantly differed in range between both methods in both planes with a mean difference of more than 3.1° (p<0.002). Results show that both methods, SPVposition and SPVsector, produce equal error values when applied with otherwise similar methodological settings and can therefore be used alternatively or within the same meta-analysis. The SPVsector, however, led to wider range values and was less frequently rated as the preferred method to represent the participants' subjective verticality.

Changes in the Organization of the Secondary Somatosensory Cortex While Processing Lumbar Proprioception and the Relationship With Sensorimotor Control in Low Back Pain

OBJECTIVES

Patients with nonspecific low back pain (NSLBP) rely more on the ankle compared with the lower back proprioception while standing, perform sit-to-stand-to-sit (STSTS) movements slower, and exhibit perceptual impairments at the lower back. However, no studies investigated whether these sensorimotor impairments relate to a reorganization of the primary and secondary somatosensory cortices (S1 and S2) and primary motor cortex (M1) during proprioceptive processing.

MATERIALS AND METHODS

Proprioceptive stimuli were applied at the lower back and ankle muscles during functional magnetic resonance imaging in 15 patients with NSLBP and 13 controls. The location of the activation peaks during the processing of proprioception within S1, S2, and M1 were determined and compared between groups. Proprioceptive use during postural control was evaluated, the duration to perform 5 STSTS movements was recorded, and participants completed the Fremantle Back Awareness Questionnaire (FreBAQ) to assess back-specific body perception.

RESULTS

The activation peak during the processing of lower back proprioception in the right S2 was shifted laterally in the NSLBP group compared with the healthy group (P=0.007). Moreover, patients with NSLSP performed STSTS movements slower (P=0.018), and reported more perceptual impairments at the lower back (P<0.001). Finally, a significant correlation between a more lateral location of the activation peak during back proprioceptive processing and a more disturbed body perception was found across the total group (ρ=0.42, P=0.025).

CONCLUSIONS

The results suggest that patients with NSLBP show a reorganization of the higher-order processing of lower back proprioception, which could negatively affect spinal control and body perception.

Does isolated somatosensory impairment affect the balance and ambulation of patients with supratentorial stroke after the acute phase?

Balance and ambulation are the result of a multicomponent control process through the interaction of the sensory and motor information. Despite the clinical relevance of the somatosensory system, its role has not drawn much attention from clinical researchers in that motor impairment is considered a major cause of dysfunction. There is little research on how somatosensory impairment alone affects functional disability after stroke. The purpose of this study was to investigate the effects of isolated somatosensory deficit on the balance and ambulation ability in patients with stroke. P38 latency of the SSEP was used to evaluate the integrity of the dorsal column-medial lemniscus pathway and the SSEP reference value was derived from the formula considering individual height and age. According to the SSEP latency, subjects were classified into 'normal', 'abnormal', and 'no response' group. A total of 110 supratentorial stroke patients with at least grade 4 of the Medical Research Council scale of lower extremity on the affected side were enrolled. Berg balance scale (BBS) and functional ambulatory categories (FAC) showed significant differences among the groups (P < 0.05). In post-hoc analysis, the BBS and FAC was significantly different between the 'normal' and 'abnormal SSEP' group (P = 0.013 for BBS, P = 0.004 for FAC) and the 'normal' and 'no response SSEP' group (P = 0.015 for BBS, P = 0.006 for FAC). We found that isolated somatosensory impairment has a negative effect on the balance and ambulation ability in patients with supratentorial stroke after the acute phase.

Time course and variability of tendinous vibration-induced postural reactions in forward and backward directions

Mechanical vibration of tendons induces large postural reactions (PR-VIB) but little is known about how these reactions vary within and between subjects. We investigated the intra- and inter-individual variability of PR-VIB and determined the reliability of center of pressure (COP) measures. Bipodal postural control (eyes closed) of 30 healthy adults were evaluated using a force platform under 02 conditions: bilateral VIB of the tibialis anterior (TA) and Achilles tendons (ACH-T) at 80 Hz. Each condition consisted of 03 trials of 30 s duration (Baseline: 10 s; VIB: 10 s; POST-VIB: 10 s). The Amplitude and Velocity of the COP in the antero-posterior/medio-lateral (AP/ML) directions were recorded and analyzed according to 5 time-windows incremented every 2 s of vibration (i.e. the first 2 s; 4 s; 6 s; 8 s & 10 s), whereas the COP position/AP was monitored every 0.5 s. All postural parameters increased significantly during TA and ACH-T vibration compared to the Baseline. The reliability of the COP measures showed good ICC scores (0.40-0.84) and measurement errors that varied depending on the duration of VIB time-windows. The COP position/AP reveals a lower intra- and inter-subject variability of PR-VIB in the first 2 s of VIB. The metrological characteristics of PR-VIB should be investigated further to guide their future use by clinicians and researchers.

Aftereffects of prolonged Achilles tendon vibration on postural control are reduced in older adults

AIM

To assess the change in the contribution of proprioceptive signal from leg muscles in postural control with ageing.

METHODS

Fifteen young (~23 yr) and fifteen older adults (~68 yr) participated in Experiment 1, which consisted of recording the mean position of the centre of pressure (CoP), CoP path length, CoP velocity, and the amplitude of the Hoffmann (H) reflex and maximal M wave (M_MAX) in the soleus muscle during upright standing, before and after 1 h of bilateral Achilles tendon vibration applied in seated posture. Eight young (~24 yr) and eight older adults (~67 yr) participated in Experiment 2 consisting of recording H-reflex and M_MAX in seated posture before and after the 1-h vibration procedure used in Experiment 1.

RESULTS

Immediately after the 1-h vibration, the mean CoP position shifted forward in both groups (p < 0.05), with a greater magnitude of change (% pre-vibration) in young [mean(SD); 74(41)%] than older adults [44(40)%; p < 0.05]. The CoP path length and velocity only increased in young adults after vibration (p < 0.05). The H-reflex amplitude decreased only in young adults after vibration [before: 35(12); after: 16(13)% M_max, p < 0.05] during upright standing (Experiment 1), whereas it decreased similarly (p > 0.05) in young [before: 47(12)% M_max; after: 28(17)% M_max] and older adults [before: 34(13)% M_max; after: 21(14)% M_max] in seated posture (Experiment 2).

CONCLUSION

Prolonged Achilles tendon vibrations lead to lesser postural perturbation in older than in young adults, supporting the assumption of a decreased reliance on leg muscle proprioception in postural control with ageing.

Effects of diagonally aligned sitting training with a tilted surface on sitting balance for low sitting performance in the early phase after stroke: a randomised controlled trial

PURPOSE

To clarify the effects of diagonally aligned sitting training using a tilted surface on sitting balance for patients with low sitting performance in the early phase after stroke.

MATERIALS AND METHODS

This was an assessor-blinded randomised controlled trial. The experimental group used a surface tilted 10° backward and down toward the most affected side; the control group trained on a horizontal surface. Both groups were asked to move their trunk diagonally forward toward the least affected side. Participants performed the activity 40 times/session for seven sessions over 8 days. Sitting performances were assessed using the function in sitting test (FIST), subjective postural vertical (SPV) on the diagonal plane, and trunk impairment scale (TIS).

RESULTS

Thirty-three stroke patients were randomly allocated into two groups. Treatment effects differed significantly: mean differences between groups for FIST (total score, static, dynamic, scooting, and reactive) were 8.96, 2.35, 3.01, 1.27, and 1.72 points, for the mean SPV value was 1.82°, and for the TIS (total score and static) were 1.87 and 1.58 points, respectively. These results were more favourable in the experimental group.

CONCLUSIONS

Diagonally aligned sitting training on a tilted surface improves sitting balance and modulates the SPV compared with a horizontal surface.

Misperception of the subjective visual vertical in neurological patients with or without stroke: A meta-analysis

BACKGROUND

The interpretation of the verticality of the environment is crucial for a proper body balance. The subjective visual vertical test (SVV) is a widely used method to determine the visual perception of the verticality, whose alteration has been related with poor functional status.

OBJECTIVE

To analyze the visual perception of the verticality in neurological patients in comparison with healthy controls.

METHODS

We searched PubMed, Scopus, and Scielo from the start of the databases until October 2017 and manually searched the reference lists of studies comparing SVV values between neurological patients and controls. Standardized mean difference (SMD) and subgroup analysis were used to analyze differences between neurological patients and healthy subjects and between stroke and non-stroke patients, respectively.

RESULTS

A total of 1,916 subjects from 31 studies were included. Neurological patients misestimate the true vertical in comparison with controls (SMD = 1.05; 95% CI: 0.81, 1.28). The misperception of the verticality was higher in stroke patients (SMD = 1.35; 95% CI: 1.02, 1.68) than in patients with other neurological conditions (SMD = 0.48; 95% CI: 0.29, 0.68).

CONCLUSIONS

Neurological patients showed a misperception of the verticality, estimated using the SVV. The neurological pathology that most alters the SVV is stroke.

Spatial orientation: Model-based approach to multi-sensory mechanisms

Perception of spatial orientation is generated through multimodal sensory integration. In this process, there are systematic errors with changes in the head or body position, which reflect challenges for the brain in maintaining a common sensory reference frame for spatial orientation. Here, we focus on this multisensory aspect of spatial orientation. We review a Bayesian spatial perception model that can be used as a framework to study sensory contributions to spatial orientation during lateral head tilts and probe neural networks involved in this process.

Differences in brain processing of proprioception related to postural control in patients with recurrent non-specific low back pain and healthy controls

Patients with non-specific low back pain (NSLBP) show an impaired postural control during standing and a slower performance of sit-to-stand-to-sit (STSTS) movements. Research suggests that these impairments could be due to an altered use of ankle compared to back proprioception. However, the neural correlates of these postural control impairments in NSLBP remain unclear. Therefore, we investigated brain activity during ankle and back proprioceptive processing by applying local muscle vibration during functional magnetic resonance imaging in 20 patients with NSLBP and 20 controls. Correlations between brain activity during proprioceptive processing and (Airaksinen et al., 2006) proprioceptive use during postural control, evaluated by using muscle vibration tasks during standing, and (Altmann et al., 2007) STSTS performance were examined across and between groups. Moreover, fear of movement was assessed. Results revealed that the NSLBP group performed worse on the STSTS task, and reported more fear compared to healthy controls. Unexpectedly, no group differences in proprioceptive use during postural control were found. However, the relationship between brain activity during proprioceptive processing and behavioral indices of proprioceptive use differed significantly between NSLBP and healthy control groups. Activity in the right amygdala during ankle proprioceptive processing correlated with an impaired proprioceptive use in the patients with NSLBP, but not in healthy controls. Moreover, while activity in the left superior parietal lobule, a sensory processing region, during back proprioceptive processing correlated with a better use of proprioception in the NSLBP group, it was associated with a less optimal use of proprioception in the control group. These findings suggest that functional brain changes during proprioceptive processing in patients with NSLBP may contribute to their postural control impairments.

Do Adolescents With Idiopathic Scoliosis Have an Erroneous Perception of the Gravitational Vertical?

STUDY DESIGN

Multicenter, case-control study.

OBJECTIVES

Demonstrate altered perception of verticality in AIS compared with matched controls.

SUMMARY OF BACKGROUND DATA

The cause of adolescent idiopathic scoliosis (AIS) remains to be found. AIS is associated with neurosensorial anomalies, in particular, altered control of orthostatic posture. During kinetic activity, the upright posture, in humans, is determined in reference to the gravitational vertical (GV). We hypothesized that in AIS, there is a discordance in the perception of the GV and the true GV. In AIS, the longitudinal axis of the body would thus be misoriented because of an erroneous perception of the GV.

METHODS

Thirty adolescents with right thoracic AIS (age 14.23 ± 1.75 years; Cobb angle 31.97°± 12.83°) and 30 controls matched for age (13.93 ± 1.85 years), body mass index, Tanner stage, and handedness were compared for subjective visual vertical (SVV) measured in static and dynamic (optokinetic stimulation) conditions, and subjective postural vertical (SPV).

RESULTS

There was no difference in the two groups, AIS and controls, for SVV. The SPV was significantly different between the two groups (p = .00023). The SPV was shifted to the right for most of the AIS patients (2.13°± 2.22°) compared with controls (-0.08°±1.40°). There was a significant correlation between SPV and clinical frontal tilt in the AIS patients.

CONCLUSION

Our findings demonstrate that patients with right thoracic AIS have an erroneous perception of the GV. In most AIS patients, SPV was shifted to the right, with no alteration of the SVV. AIS might be the consequence of a reoriented longitudinal body axis aligned with an erroneous vertical reference. The underlying mechanism might involve dysfunction of trunk graviceptors. The primary or secondary nature of this dysfunction remains an open question.

Proprioceptive Weighting Ratio for Balance Control in Static Standing Is Reduced in Elderly Patients With Non-Specific Low Back Pain

MINI: Elderly patients older than 65 years were divided into non-specific low back pain (NSLBP) and non-LBP (NLBP) groups. The postural control study of the relative contributions of different proprioceptive signals (relative proprioceptive weighting ratio [RPW]) revealed lower leg proprioceptive decreases (RPW 240 Hz) in NSLBP compared to NLBP.

STUDY DESIGN

A cross-sectional, observational study.

OBJECTIVE

The aim of this study was to determine a specific proprioceptive control strategy during postural balance in elderly patients with non-specific low back pain (NSLBP) and non-LBP (NLBP).

SUMMARY OF BACKGROUND DATA

Proprioceptive decline is an important risk factor for decreased balance control in elderly patients with NSLBP. The resulting reduction in proprioception in the trunk or lower legs may contribute to a reduction in postural sway. This study aims to determine the specific proprioceptive control strategy used during postural balance in elderly patients with NSLBP and NLBP and to assess whether this strategy is related to proprioceptive decline in NSLBP.

METHODS

Pressure displacement centers were determined in 28 elderly patients with NSLBP and 46 elderly patients with NLBP during upright stances on a balance board without the benefit of vision. Gastrocnemius and lumbar multifidus muscle vibratory stimulations at 30, 60, and 240 Hz, respectively, were applied to evaluate the relative contributions of the different proprioceptive signals (relative proprioceptive weighting ratio, RPW) used in postural control.

RESULTS

Compared to elderly patients with NLBP, those with NSLBP had a lower RPW at 240 Hz and significantly higher RPW at 30 Hz. A logistic regression analysis showed that RPW at 240 Hz was independently associated with NSLBP after controlling for confounding factors.

CONCLUSION

Elderly patients with NSLBP decreased their reliance on ankle strategy (RPW at 240 Hz) and hip strategy (RPW at 30 Hz) proprioceptive signals during balance control. The inability to control hip and ankle strategies indicates a deficit of postural control and is hypothesized to result from proprioceptive impairment. Moreover, elderly patients with NSLBP are at higher risk for lower leg proprioceptive decrease (240 Hz) through the NSLBP exacerbation.

LEVEL OF EVIDENCE

4.

Plantar cutaneous afferents influence the perception of Subjective Visual Vertical in quiet stance

The estimation of Subjective Visual Vertical (SVV) involves the allocentric, gravitational and egocentric references, which are built by visual, vestibular and somatosensory afferents. Our goals were to assess the influence of plantar cutaneous afferents on the perception of SVV, and to see if there is a difference according to the efficiency of plantar cutaneous afferents. We recruited 48 young and healthy subjects and assessed their SVV and postural performances in quiet stance with a force platform, at 40 or 200 cm, in four ground conditions: on firm ground, on foam, with a bilateral, or with a unilateral 3 mm arch support. We also assessed the efficiency of our subjects' plantar afferents with the plantar quotient method and divided them in two groups: subjects with a normal use of plantar afferents and subjects with Plantar Exteroceptive Inefficiency (PEI). The results showed significant decreases in the counter clockwise SVV deviation only with the unilateral arch support, at near distance, and among the typically behaving subjects. We conclude that asymmetric foot cutaneous afferents are able to bias the egocentric vertical reference and hence influence the perception of SVV. This influence disappears among subjects with PEI, probably because of a distortion of the plantar signal.

Normative data for human postural vertical: A systematic review and meta-analysis

Perception of verticality is required for normal daily function, yet the typical human detection error range has not been well characterized. Vertical misperception has been correlated with poor postural control and functionality in patients after stroke and after vestibular disorders. Until now, all the published studies that assessed Subjective Postural Vertical (SPV) in the seated position used small groups to establish a reference value. However, this sample size does not represent the healthy population for comparison with conditions resulting in pathological vertical. Therefore, the primary objective was to conduct a systematic review with meta-analyses of Subjective Postural Vertical (SPV) data in seated position in healthy adults to establish the reference value with a representative sample. The secondary objective was to investigate the methodological characteristics of different assessment protocols of SPV described in the literature. A systematic literature search was conducted using Medline, EMBASE, and Cochrane libraries. Mean and standard deviation of SPV in frontal and sagittal planes were considered as effect size measures. Sixteen of 129 identified studies met eligibility criteria for our systematic review (n = 337 subjects in the frontal plane; n = 187 subjects in sagittal plane). The meta-analyses measure was estimated using the pooled mean as the estimator and its respective error. Mean reference values were 0.12°±1.49° for the frontal plane and 0.02°±1.82° for the sagittal plane. There was a small variability of the results and this systematic review resulted in representative values for SPV. The critical analysis of the studies and observed homogeneity in the sample suggests that the methodological differences used in the studies did not influence SPV assessment of directional bias in healthy subjects. These data can serve as a reference for clinical studies in disorders of verticality.

Parkinson's disease versus ageing: different postural responses to soleus muscle vibration

BACKGROUND

Impairments of postural stability occur with increasing age and in neurodegenerative diseases like the Parkinson's disease (PD). While changes in balance have been described in many studies under steady-state conditions, less is known about the dynamic changes in balance following sudden transition to different sensory inputs.

RESEARCH QUESTION

The aim was to clarify different effects of age and Parkinson's disease on dynamic postural responses immediately after lower leg muscle stimulation offset. Sudden removing of active sensory input represents a transient period in balance control.

METHODS

Postural responses of 13 young, 13 healthy elderly and 13 PD patients to proprioceptive bilateral vibration of soleus muscles during stance were assessed by a force platform and two accelerometers attached on the upper and the lower trunk. The experimental protocol consisted of 2 conditions of soleus muscle vibration with 1) eyes open and 2) eyes closed randomly repeated four times.

RESULTS

During vibration period before stimulus offset, postural responses were similar in elderly and PD patients. Contrary, immediately after vibration offset significantly larger backward amplitude of centre of foot pressure (CoP) displacement and trunk tilts were observed in PD patients compared to healthy peers. In returning to vertical position, peak-to-peak amplitudes, maximal velocity of CoP and trunk tilts significantly increased in PD patients. Without vision, their postural responses were more enhanced. The differences between young and elderly were found in most parameters in transient period after vibration offset and also during vibration.

SIGNIFICANCE

The PD patients showed more unstable transient postural responses to selective sensory stimulation switch off, which may reflect impairment of sensory reweighting in balance control. Understanding how early stages PD patients differ in balance control from neurologically intact peers may help researchers and clinicians to refine their intervention and fall prevention programs.

Subjective Visual Vertical in Idiopathic Bilateral Vestibular Hypofunction: Enhanced Role of Vision, Neck, and Body Proprioception

INTRODUCTION

We aimed to study the participation of proprioceptive and visual inputs in subjective visual vertical (SVV) in bilateral vestibular hypofunction and in normal subjects.

STUDY DESIGN

Prospective case-control study.

SETTING

Tertiary referral center.

MATERIALS AND METHODS

SVV (six replicates) was measured on a tiltable rehabilitation seat in 26 adult patients with idiopathic bilateral vestibular hypofunction (IBVH) and 33 adult controls. Subjects were asked to place vertically a 45 degrees-tilted red line on a screen (three replicates to left and three to right alternatively) using a remote control in total darkness and in seven body positions: vertical, head, and body left- and right-tilts to 12 and 24 degrees, and then body left- and right-tilt to 24 degrees with the head upright.

RESULTS

In the vertical position, SVV did not differ between IBVH and controls. Patients with IBVH were more sensitive to body tilt than controls (SVV: -8.1 ± 4.66 degrees for IBVH versus -0.2 ± 3.23 for control at 24 degrees body and head left-tilt, p < 0.0001, unpaired t test). The visual attraction effect defined by a deviation of the SVV to the side of the initial line presentation appeared to be higher in the IBVH than in controls suggesting higher visual dependence in IBVH. Placing the head upright while the body was still tilted significantly reduced this difference. Similar results were observed for the right-tilts.

CONCLUSION

Not only otolithic function but also visual plus body and neck proprioceptive entries participate in SVV. The influence of vision and proprioception appears to be enhanced in case of IBVH.

Center of Pressure Motion After Calf Vibration Is More Random in Fallers Than Non-fallers: Prospective Study of Older Individuals

Aging is associated with changes in balance control and elderly take longer to adapt to changing sensory conditions, which may increase falls risk. Low amplitude calf muscle vibration stimulates local sensory afferents/receptors and affects sense of upright when applied in stance. It has been used to assess the extent the nervous system relies on calf muscle somatosensory information and to rapidly change/perturb part of the somatosensory information causing balance unsteadiness by addition and removal of the vibratory stimulus. This study assessed the effect of addition and removal of calf vibration on balance control (in the absence of vision) in elderly individuals (>65 years, n = 99) who did (n = 41) or did not prospectively report falls (n = 58), and in a group of young individuals (18-25 years, n = 23). Participants stood barefoot and blindfolded on a force plate for 135 s. Vibrators (60 Hz, 1 mm) attached bilaterally over the triceps surae muscles were activated twice for 15 s; after 15 and 75 s (45 s for recovery). Balance measures were applied in a windowed (15 s epoch) manner to compare center-of-pressure (CoP) motion before, during and after removal of calf vibration between groups. In each epoch, CoP motion was quantified using linear measures, and non-linear measures to assess temporal structure of CoP motion [using recurrence quantification analysis (RQA) and detrended fluctuation analysis]. Mean CoP displacement during and after vibration did not differ between groups, which suggests that calf proprioception and/or weighting assigned by the nervous system to calf proprioception was similar for the young and both groups of older individuals. Overall, compared to the elderly, CoP motion of young was more predictable and persistent. Balance measures were not different between fallers and non-fallers before and during vibration. However, non-linear aspects of CoP motion of fallers and non-fallers differed after removal of vibration, when dynamic re-weighting is required. During this period fallers exhibited more random CoP motion, which could result from a reduced ability to control balance and/or a reduced ability to dynamically reweight proprioceptive information. These results show that non-linear measures of balance provide evidence for deficits in balance control in people who go on to fall in the following 12 months.

Perception of body movement when real and simulated displacements are combined

Muscle-tendon vibration has often been used to study the contribution of proprioception to kinesthesia and postural control. This technique is known to simulate the lengthening of the vibrated muscle and, in the presence of balance constraints, evoke compensatory postural responses. The objective of the present study was to clarify the consequences of this stimulation on the dynamic features of whole-body movement perception in upright stance and in the absence of balance constraints. Eleven participants were restrained in a dark room on a motorized backboard that was able to tilt the upright body around the ankle joints. The participants were passively tilted backwards or forwards with a maximum amplitude of four degrees and at very low acceleration (thus preventing the semicircular canals from contributing to movement perception). In half the trials, the body displacement was combined with continuous vibration of the Achilles tendons, which simulates a forward tilt. Participants used a joystick to report when and in which direction they perceived their own whole-body movement. Our results showed that during backward whole-body displacement, the movement detection threshold (i.e. the minimum angular velocity required to accurately perceive passive displacement) was higher in the presence of vibration, whereas the accuracy rate (i.e. the proportion of the overall trial duration during which the movement was correctly indicated) was lower. Conversely, the accuracy rate for forward displacements was higher in the presence of vibration. In the absence of vibration, forward movement was detected earlier than backward movement. The simulated whole-body displacement evoked by Achilles tendon vibration was therefore able to either enhance or disrupt the perception of real, slow, whole-body tilt movements, depending on the congruence between the direction of real and simulated displacements.

Disturbance of verticality perception and postural dysfunction in Parkinson's disease

OBJECTIVES

Verticality perception is known to be abnormal in Parkinson's disease (PD), but in which stage respective dysfunctions arise and how they relate to postural disorders remains to be settled. These issues were studied with respect to different dimensions of the subjective visual vertical (SVV) in relation to clinical parameters of postural control.

MATERIALS & METHODS

All participants had to orientate a luminous line at random planar orientations to a strictly vertical position using an automated operator system. The SVV was analyzed in 58 PD patients and 28 control subjects with respect to (i) the angle between true and subjective vertical (deviation) and (ii) the variability of this across five measurements (variability). Results were referred to the subjective upright head position (SUH), the disease stage, and clinical gait/balance features assessed by the MDS-UPDRS and the Tinetti test.

RESULTS

Parkinson's disease patients had significantly higher SVV deviation and variability than controls. With respect to disease stage, deviation developed before abnormal variability. SVV variability was associated with poor balance and gait performance, as well as postural instability. Deficits in SUH and SVV deviation were correlated and mostly unidirectional, but did not correspond to the side of motor symptom dominance.

CONCLUSIONS

Visual verticality perception in PD is deviated already in early stages, conceivably as a relatively static internal misrepresentation of object orientation. Variability about verticality perception emerges in more advanced stages and is associated with postural and balance abnormalities.

Gravity estimation and verticality perception

Gravity is a defining force that governs the evolution of mechanical forms, shapes and anchors our perception of the environment, and imposes fundamental constraints on our interactions with the world. Within the animal kingdom, humans are relatively unique in having evolved a vertical, bipedal posture. Although a vertical posture confers numerous benefits, it also renders us less stable than quadrupeds, increasing susceptibility to falls. The ability to accurately and precisely estimate our orientation relative to gravity is therefore of utmost importance. Here we review sensory information and computational processes underlying gravity estimation and verticality perception. Central to gravity estimation and verticality perception is multisensory cue combination, which serves to improve the precision of perception and resolve ambiguities in sensory representations by combining information from across the visual, vestibular, and somatosensory systems. We additionally review experimental paradigms for evaluating verticality perception, and discuss how particular disorders affect the perception of upright. Together, the work reviewed here highlights the critical role of multisensory cue combination in gravity estimation, verticality perception, and creating stable gravity-centered representations of our environment.

The Bobath concept - a model to illustrate clinical practice

Background and purpose: The model of Bobath clinical practice provides a framework identifying the unique aspects of the Bobath concept in terms of contemporary neurological rehabilitation. The utilisation of a framework to illustrate the clinical application of the Bobath concept provides the basis for a common understanding with respect to Bobath clinical practice, education, and research. The development process culminating in the model of Bobath clinical practice is described. Case description: The use of the model in clinical practice is illustrated using two cases: a client with a chronic incomplete spinal cord injury and a client with a stroke. Discussion: This article describes the clinical application of the Bobath concept in terms of the integration of posture and movement with respect to the quality of task performance, applying the Model of Bobath Clinical Practice. Facilitation, a key aspect of Bobath clinical practice, was utilised to positively affect motor control and perception in two clients with impairment-related movement problems due to neurological pathology and associated activity limitations and participation restrictions - the outcome measures used to reflect the individual clinical presentation. Implications for Rehabilitation The model of Bobath clinical practice provides a framework identifying the unique aspects of the Bobath-concept. The model of Bobath clinical practice provides the basis for a common understanding with respect to Bobath clinical practice, education, and research. The clinical application of the Bobath-concept highlights the integration of posture and movement with respect to the quality of task performance. Facilitation, a key aspect of Bobath clinical practice, positively affects motor control, and perception.

Examination of reactive motor responses to Achilles tendon vibrations during an inhibitory stepping reaction time task

Inhibition is known to influence balance, step initiation and gait control. A specific subcomponent of inhibition, the perceptual inhibition process, has been suggested to be specifically involved in the integration of proprioceptive information that is necessary for efficient postural responses. This study aimed to investigate the inhibition requirements of planning and executing a choice step initiation task in young adults following experimental perturbation of proprioceptive information using Achilles tendon vibrations. We developed an inhibitory stepping reaction time task in which participants had to step in response to visual arrows that manipulated specific perceptual or motor inhibition according to two proprioceptive configurations: without or with application of vibrations. Performance of twenty-eight participants (mean age 21 years) showed that Achilles tendon vibrations induced an increase in attentional demands (higher reaction time and longer motor responses). Further, this increase in attentional demands did not affect specifically the different inhibitory processes tested in this reactive stepping task. It suggests that attentional demands associated with the vibratory perturbation to postural control do not lead to a shift from automatic to more attentional inhibition processes, at least in young adults.

Perception of Upright: Multisensory Convergence and the Role of Temporo-Parietal Cortex

We inherently maintain a stable perception of the world despite frequent changes in the head, eye, and body positions. Such "orientation constancy" is a prerequisite for coherent spatial perception and sensorimotor planning. As a multimodal sensory reference, perception of upright represents neural processes that subserve orientation constancy through integration of sensory information encoding the eye, head, and body positions. Although perception of upright is distinct from perception of body orientation, they share similar neural substrates within the cerebral cortical networks involved in perception of spatial orientation. These cortical networks, mainly within the temporo-parietal junction, are crucial for multisensory processing and integration that generate sensory reference frames for coherent perception of self-position and extrapersonal space transformations. In this review, we focus on these neural mechanisms and discuss (i) neurobehavioral aspects of orientation constancy, (ii) sensory models that address the neurophysiology underlying perception of upright, and (iii) the current evidence for the role of cerebral cortex in perception of upright and orientation constancy, including findings from the neurological disorders that affect cortical function.

Ehlers-Danlos Syndrome, Hypermobility Type: Impact of Somatosensory Orthoses on Postural Control (A Pilot Study)

Elhers-Danlos syndrome (EDS) is the clinical manifestation of connective tissue disorders, and comprises several clinical forms with no specific symptoms and selective medical examinations which result in a delay in diagnosis of about 10 years. The EDS hypermobility type (hEDS) is characterized by generalized joint hypermobility, variable skin hyperextensibility and impaired proprioception. Since somatosensory processing and multisensory integration are crucial for both perception and action, we put forth the hypothesis that somatosensory deficits in hEDS patients may lead, among other clinical symptoms, to misperception of verticality and postural instability. Therefore, the purpose of this study was twofold: (i) to assess the impact of somatosensory deficit on subjective visual vertical (SVV) and postural stability; and (ii) to quantify the effect of wearing somatosensory orthoses (i.e., compressive garments and insoles) on postural stability. Six hEDS patients and six age- and gender-matched controls underwent a SVV (sitting, standing, lying on the right side) evaluation and a postural control evaluation on a force platform (Synapsys), with or without visual information (eyes open (EO)/eyes closed (EC)). These two latter conditions performed either without orthoses, or with compression garments (CG), or insoles, or both. Results showed that patients did not exhibit a substantial perceived tilt of the visual vertical in the direction of the body tilt (Aubert effect) as did the control subjects. Interestingly, such differential effects were only apparent when the rod was initially positioned to the left of the vertical axis (opposite the longitudinal body axis). In addition, patients showed greater postural instability (sway area) than the controls. The removal of vision exacerbated this instability, especially in the mediolateral (ML) direction. The wearing of orthoses improved postural stability, especially in the eyes-closed condition, with a particularly marked effect in the anteroposterior (AP) direction. Hence, this study suggests that hEDS is associated with changes in the relative contributions of somatosensory and vestibular inputs to verticality perception. Moreover, postural control impairment was offset, at least partially, by wearing somatosensory orthoses.

Gravity as a Strong Prior: Implications for Perception and Action

In the future, humans are likely to be exposed to environments with altered gravity conditions, be it only visually (Virtual and Augmented Reality), or visually and bodily (space travel). As visually and bodily perceived gravity as well as an interiorized representation of earth gravity are involved in a series of tasks, such as catching, grasping, body orientation estimation and spatial inferences, humans will need to adapt to these new gravity conditions. Performance under earth gravity discrepant conditions has been shown to be relatively poor, and few studies conducted in gravity adaptation are rather discouraging. Especially in VR on earth, conflicts between bodily and visual gravity cues seem to make a full adaptation to visually perceived earth-discrepant gravities nearly impossible, and even in space, when visual and bodily cues are congruent, adaptation is extremely slow. We invoke a Bayesian framework for gravity related perceptual processes, in which earth gravity holds the status of a so called “strong prior”. As other strong priors, the gravity prior has developed through years and years of experience in an earth gravity environment. For this reason, the reliability of this representation is extremely high and overrules any sensory information to its contrary. While also other factors such as the multisensory nature of gravity perception need to be taken into account, we present the strong prior account as a unifying explanation for empirical results in gravity perception and adaptation to earth-discrepant gravities.

Change in the natural head-neck orientation momentarily altered sensorimotor control during sensory transition

Achilles tendon vibration generates proprioceptive information that is incongruent with the actual body position; it alters the perception of body orientation leading to a vibration-induced postural response. When a person is standing freely, vibration of the Achilles tendon shifts the internal representation of the verticality backward thus the vibration-induced postural response realigned the whole body orientation with the shifted subjective vertical. Because utricular otoliths information participates in the creation of the internal representation of the verticality, changing the natural orientation of the head-neck system during Achilles tendon vibration could alter the internal representation of the earth vertical to a greater extent. Consequently, it was hypothesized that compared to neutral head-neck orientation, alteration in the head-neck orientation should impair balance control immediately after Achilles tendon vibration onset or offset (i.e., sensory transition) as accurate perception of the earth vertical is required. Results revealed that balance control impairment was observed only immediately following Achilles tendon vibration offset; both groups with the head-neck either extended or flexed showed larger body sway (i.e., larger root mean square scalar distance between the center of pressure and center of gravity) compared to the group with the neutral head-neck orientation. The fact that balance control was uninfluenced by head-neck orientation immediately following vibration onset suggests the error signal needs to accumulate to a certain threshold before the internal representation of the earth vertical becomes incorrect.

Functional Neuroanatomy for Posture and Gait Control

Here we argue functional neuroanatomy for posture-gait control. Multi-sensory information such as somatosensory, visual and vestibular sensation act on various areas of the brain so that adaptable posture-gait control can be achieved. Automatic process of gait, which is steady-state stepping movements associating with postural reflexes including headeye coordination accompanied by appropriate alignment of body segments and optimal level of postural muscle tone, is mediated by the descending pathways from the brainstem to the spinal cord. Particularly, reticulospinal pathways arising from the lateral part of the mesopontine tegmentum and spinal locomotor network contribute to this process. On the other hand, walking in unfamiliar circumstance requires cognitive process of postural control, which depends on knowledges of self-body, such as body schema and body motion in space. The cognitive information is produced at the temporoparietal association cortex, and is fundamental to sustention of vertical posture and construction of motor programs. The programs in the motor cortical areas run to execute anticipatory postural adjustment that is optimal for achievement of goal-directed movements. The basal ganglia and cerebellum may affect both the automatic and cognitive processes of posturegait control through reciprocal connections with the brainstem and cerebral cortex, respectively. Consequently, impairments in cognitive function by damages in the cerebral cortex, basal ganglia and cerebellum may disturb posture-gait control, resulting in falling.

Verticality Perceptions Associate with Postural Control and Functionality in Stroke Patients

Deficits of postural control and perceptions of verticality are disabling problems observed in stroke patients that have been recently correlated to each other. However, there is no evidence in the literature confirming this relationship with quantitative posturography analysis. Therefore, the objectives of the present study were to analyze the relationship between Subjective Postural Vertical (SPV) and Haptic Vertical (HV) with posturography and functionality in stroke patients. We included 45 stroke patients. The study protocol was composed by clinical interview, evaluation of SPV and HV in roll and pitch planes and posturography. Posturography was measured in the sitting and standing positions under the conditions: eyes open, stable surface (EOSS); eyes closed, stable surface (ECSS); eyes open, unstable surface (EOUS); and eyes closed, unstable surface (ECUS). The median PV in roll plane was 0.34° (-1.44° to 2.54°) and in pitch plane 0.36° (-2.72° to 2.45°). The median of HV in roll and pitch planes were -0.94° (-5.86° to 3.84°) and 3.56° (-0.68° to 8.36°), respectively. SPV in the roll plane was correlated with all posturagraphy parameters in sitting position in all conditions (r = 0.35 to 0.47; p < 0.006). There were moderate correlations with the verticality perceptions and all the functional scales. Linear regression model showed association between speed and SPV in the roll plane in the condition EOSS (R2 of 0.37; p = 0.005), in the condition ECSS (R2 of 0.13; p = 0.04) and in the condition EOUS (R2 of 0.22; p = 0.03). These results suggest that verticality perception is a relevant component of postural control and should be systematically evaluated, particularly in patients with abnormal postural control.

PARKINSON'S DISEASE PATIENTS WITH DOMINANT HEMIBODY AFFECTED BY THE DISEASE RELY MORE ON VISION TO MAINTAIN UPRIGHT POSTURAL CONTROL

This study assesses the association between disease onset side (dominant or non-dominant) and vision on postural control of Parkinson's disease patients. Patient volunteers composed two groups, according to the onset side affected: Dominant group (n=9; M age=66.1 yr., SD=7.2; 6 women, 3 men) and Non-dominant group (n=9; M age=67.4 yr., SD=6.4; 6 women, 3 men). The groups' postural control was assessed by posturography during quiet upright stance in two conditions, Eyes open and Eyes closed. Two-way analyses of variance (ANOVAs; group×condition) with repeated measures for the second factor assessed the differences associated with affected hemibody and vision on postural control. Analyses indicated that patients with the dominant side affected also presented significantly greater variation in center of pressure than those with the non-dominant side affected, mainly in the Eyes closed condition. The results demonstrate a higher reliance on vision in the dominant side, possibly to compensate somatosensory system impairments. These results also highlight the importance of analyzing the hemibody affected by the disease when postural control is assessed in this population.

The right temporoparietal junction plays a causal role in maintaining the internal representation of verticality

Perception of the visual vertical is strongly based on our ability to match visual inflow with vestibular, proprioceptive, tactile, and even visceral information that contributes to maintaining an internal representation of the vertical. An important cortical region implicated in multisensory integration is the right temporoparietal junction (rTPJ), which also is involved in higher order forms of body- and space-related cognition. To test whether this region integrates body-related multisensory information necessary for establishing the subjective visual vertical, we combined a psychophysical task (the rod-and-frame test) with transient inhibition of the rTPJ via continuous theta burst stimulation (cTBS). A Gabor patch visual detection task was used as a control visual task. cTBS of early visual cortex (V1-V3) was used to test whether early visual cortices played any role in verticality estimation. We show that inhibition of rTPJ activity selectively impairs the ability to evaluate the rod's verticality when no contextual visual information, such as a frame surrounding the rod, is provided. Conversely, transient inhibition of V1-V3 selectively disrupts the ability to visually detect Gabor patch orientation. This anatomofunctional dissociation supports the idea that the rTPJ plays a causal role in integrating egocentric sensory information encoded in different reference systems (i.e., vestibular and somatic) to maintain an internal representation of verticality.

Sensorimotor and cognitive factors associated with the age-related increase of visual field dependence: a cross-sectional study

Reliance on the visual frame of reference for spatial orientation (or visual field dependence) has been reported to increase with age. This has implications on old adults' daily living tasks as it affects stability, attention, and adaptation capacities. However, the nature and underlying mechanisms of this increase are not well defined. We investigated sensorimotor and cognitive factors possibly associated with increased visual field dependence in old age, by considering functions that are both known to degrade with age and important for spatial orientation and sensorimotor control: reliance on the (somatosensory-based) egocentric frame of reference, visual fixation stability, and attentional processing of complex visual scenes (useful field of view, UFOV). Twenty young, 18 middle-aged, and 20 old adults completed a visual examination, three tests of visual field dependence (RFT, RDT, and GEFT), a test of egocentric dependence (subjective vertical estimation with the body erect and tilted at 70°), a visual fixation task, and a test of visual attentional processing (UFOV®). Increased visual field dependence with age was associated with reduced egocentric dependence, visual fixation stability, and visual attentional processing. In addition, visual fixation instability and reduced UFOV were correlated. Results of middle-aged adults fell between those of the young and old, revealing the progressive nature of the age effects we evaluated. We discuss results in terms of reference frame selection with respect to ageing as well as visual and non-visual information processing. Inter-individual differences amongst old adults are highlighted and discussed with respect to the functionality of increased visual field dependence.

Relationship between paraspinal muscle cross-sectional area and relative proprioceptive weighting ratio of older persons with lumbar spondylosis

[Purpose] The purpose of this study was to examine the relationship between the paraspinal muscle cross-sectional area and the relative proprioceptive weighting ratio during local vibratory stimulation of older persons with lumbar spondylosis in an upright position. [Subjects] In all, 74 older persons hospitalized for lumbar spondylosis were included. [Methods] We measured the relative proprioceptive weighting ratio of postural sway using a Wii board while vibratory stimulations of 30, 60, or 240 Hz were applied to the subjects’ paraspinal or gastrocnemius muscles. Back strength, abdominal muscle strength, and erector spinae muscle (L1/L2, L4/L5) and lumbar multifidus (L1/L2, L4/L5) cross-sectional areas were evaluated. [Results] The erector spinae muscle (L1/L2) cross-sectional area was associated with the relative proprioceptive weighting ratio during 60Hz stimulation. [Conclusion] These findings show that the relative proprioceptive weighting ratio compared to the erector spinae muscle (L1/L2) cross-sectional area under 60Hz proprioceptive stimulation might be a good indicator of trunk proprioceptive sensitivity.

Neck proprioception shapes body orientation and perception of motion

This review article deals with some effects of neck muscle proprioception on human balance, gait trajectory, subjective straight-ahead (SSA), and self-motion perception. These effects are easily observed during neck muscle vibration, a strong stimulus for the spindle primary afferent fibers. We first remind the early findings on human balance, gait trajectory, SSA, induced by limb, and neck muscle vibration. Then, more recent findings on self-motion perception of vestibular origin are described. The use of a vestibular asymmetric yaw-rotation stimulus for emphasizing the proprioceptive modulation of motion perception from the neck is mentioned. In addition, an attempt has been made to conjointly discuss the effects of unilateral neck proprioception on motion perception, SSA, and walking trajectory. Neck vibration also induces persistent aftereffects on the SSA and on self-motion perception of vestibular origin. These perceptive effects depend on intensity, duration, side of the conditioning vibratory stimulation, and on muscle status. These effects can be maintained for hours when prolonged high-frequency vibration is superimposed on muscle contraction. Overall, this brief outline emphasizes the contribution of neck muscle inflow to the construction and fine-tuning of perception of body orientation and motion. Furthermore, it indicates that tonic neck-proprioceptive input may induce persistent influences on the subject's mental representation of space. These plastic changes might adapt motion sensitiveness to lasting or permanent head positional or motor changes.