Automatic postural response systems in individuals with congenital total blindness

Neuronal Control of Posture in Blind Individuals

The control of posture is guided by the integration of sensory information. Because blind individuals cannot apply visual information to control posture as sighted individuals do they must compensate by the remaining senses. We therefore hypothesize that blind individuals alter their brain activation in the sensorimotor cortex during postural control to compensate for balance control without vision by the increased integration of somatosensory information. Ten blind and ten sighted (matched) individuals controlled posture during conditions with (I) eyes closed / open, and (II) stable / unstable surface conditions. Postural sway was recorded by applying a pressure distribution measuring plate. Brain activation was collected by functional Near InfraRed Spectroscopy (fNIRS) above motor-sensory cortices of the right and left hemispheres. Blind individuals showed significantly increased postural sway when balancing with open eyes on an unstable surface and when compared to sighted individuals. Whereas blind individuals showed significantly increased brain activation when balancing with open eyes on stable and unstable surface conditions, sighted individuals increased their brain oxygenation only during closed eyes and unstable surface conditions. Overall conditions, blind individuals presented significantly increased brain activation in two channels of the left and right hemispheric motor-sensory cortex when compared to sighted individuals. We therefore conclude that sighted individuals increase their brain oxygenation in the sensorimotor cortex during postural control tasks that demand sensory integration processes. Blind individuals are characterized by increased brain activation overall conditions indicating additional sensory integration during postural control. Thus, the sensorimotor cortex of blind individuals adapts to control posture without vision.

Orthopaedic problems in the blind

Background

Blindness is a common problem in every society and country. The problem ranges from complete blindness to partially sighted in the affected population. India has close to 12 million visually impaired people. Orthopaedic problems are not uncommon in blind. Orthopaedic Surgeons though had been aware of the postural and gait abnormalities in blind but very few published studies have systematically focused on the effect of blindness on the development of posture and gait.

Methods

Case Control study done for the orthopaedic evaluation of the blind and partially sighted individuals. The study population included 242 students of Ahmadi School for the Blind, Aligarh Muslim University, Aligarh (India), as the cases and another matched set of 250 non-blind children. All the children were assessed for the orthopaedic problems like degree of ligamentous laxity, spinal alignment, foot morphology and alignment of hips, knees and ankles. Standing posture and gait were also examined and recorded. Ligamentous laxity was assessed according to the method adopted by Beighton et al.10 Chi-square test was applied using IBM SPSS 23.0.

Results

139 children (57.4 %) were found to have laxity of the ligaments. 72 children (29.7 %) had spine deformities, out of which kyphosis was present in 34 (47.2 %), scoliosis in 23 (31.9 %), lordosis in 13 (18.0 %), and meningomyelocele in 2 (2.9 %) children. 119 children (49.1 %) had foot deformities. 37 children (15.2 %) had knee deformity. 22 children (9.0 %) showed evidence of cerebral palsy. 216 children (89.2 %) had varying degrees of postural abnormalities. The data was statistically significant when compared with the control group (P < 0.05).

Conclusion

Blindness causes a wide range of complicated sensory and motor problems that frequently forces people into isolation. Blind rehabilitation requires an interdisciplinary approach. Orthopaedic problems are quite common in blind individuals and should be dealt separately.

Assessment of functional mobility and gait during a timed up and go test in adults with total blindness

BACKGROUND

The loss of vision leads to behavioral and motor adaptations that do not necessarily translate to good functioning with regards to daily tasks.

AIM

To investigate differences in functional mobility in adults with total blindness, and analyze differences in spatiotemporal gait variables with and without the use of a cane, and wearing shoes or barefoot.

METHODS

We used an inertial measurement unit to assess the spatiotemporal parameters of the gait and functional mobility in seven subjects with total blindness and four sighted participants during the timed up and go test (TUG) test performed under conditions: barefoot/shod; and with/without a cane (blind subjects).

RESULTS

Significant differences between groups were found in total TUG test time and in the sub-phases when the blind subjects executed the TUG barefoot and without a cane (p < .01). Other differences were found in trunk movement during sit-to-stand, and stand-to-sit where blind subjects when without cane and barefoot, they had a greater range of motion than sighted subjects (p < .01). Also, BMI has a moderate to strong influence in the execution of the TUG in blind subjects (p < .05) CONCLUSION: This study showed that, when using a gait-assistance device and wearing shoes, blind subjects have similar functional mobility and gait as sighted subjects, suggesting that an external haptic reference can compensate for the lack of vision. Knowledge of these differences can provide a better understanding of the adaptive behavior in this population, thereby assisting in minimizing the occurrence of trauma and falls.

Effects of the Interference of Sensory Systems on Postural Control in Congenitally Blind Subjects

The postural system requires the sensory systems to maintain postural control (PC). Blind subjects use the somatosensory system to keep PC whereas sighted subjects use the visual system. So what happens to PC when challenging the sensory systems? We analyzed the center of pressure (COP) in ten blind and 10 sighted subjects under conditions: eyes open/closed (interference of visual system) and on firm/foam surfaces (interference of somatosensory system). We found that under the condition of eyes open on a firm surface, the blind subjects relied on the somatosensory system, whereas sighted subjects relied on the visual system. However, when eyes closed and on foam surface, similar behavior was found in both groups for all COP variables. In general blind subjects use their somatosensory system as the main sensory input to maintain PC.

Body Balance of Children and Youths with Visual Impairment (Pilot Study)

AIM

The study was designed to assess the effects of surface instability in the response of the balance control system in children and youths with visual impairment (BL) and in normally sighted controls (NE).

MATERIALS AND METHODS

The empirical research study involved 80 individuals, aged from 6 to 20 years, with a mean age of 14.37 (±4.68), including 40 blind individuals and a randomly selected control group 40 normally sighted. Stabilometric measurements were performed with the use of the Platform CQ Stab 2P, with eyes open (EO) and closed (EC) on the solid surface, and then, the same procedure was performed on the platform covered with 1-centimetre-thick foam.

RESULTS

Statistical analyses (Wilcoxon matched-pairs test, Mann-Whitney U test) of the results identified during the trials reveal the following findings in the BL group in the EO and EC tests. The results of the foam surface test were higher and the differences were statistically significant in the BL group (sway path EO p = 0.009, EC p = 0.006; mean amplitude EC p = 0.030; mean velocity EO p = 0.009, EC p = 0.006; sway area EO p = 0.017, EC p = 0.009; and number of COP deflections along the sagittal plane EO p = 0.004). No similar correlations were observed in the NE group, except for the mean amplitude EO p = 0.033 and sway area EO p = 0.030. There was one difference between the BL and the NE group for the mean amplitude parameter, p = 0.018, in a solid surface test with open eyes. The results were higher in the BL group.

CONCLUSIONS

The present study showed no worse balance in the BL group than in the NE group but worse performance on the foam than without it. It indicates the need to develop body balance skills in blind people by improving their proprioceptive sensitivity. In everyday life and training, blind people should experience exteroceptive stimuli, different textures, and unstable surfaces as much as possible.

Effect of static and dynamic jaw positions on postural stability among people with blindness

BACKGROUND

In comparison with the people with normal sight, the mean center of gravity (COG) velocity is significantly higher among blind people. A strong relationship has been shown between jaw and neck sensorimotor and postural control. The purpose of this study was to determine the effect of different static and dynamic jaw positions on postural stability among subjects with blindness.

METHODS

Postural stability was measured as COG velocity in 39 blind subjects under the following five conditions: resting jaw (natural jaw position with no instructions, control), open jaw (teeth of both jaws slightly apart), clenched jaw (teeth tightly closed across each other), chewing (a standard bolus of gum at the natural palace), and tongue position (positioned behind the upper incisors) while standing on firm and foam surfaces.

RESULTS

The mean COG velocity while standing on the firm surface during resting, open jaw position, clenched jaw position, chewing, and tongue positions were 0.54, 0.50, 0.44, 0.59, and 0.46 deg/s, respectively. The mean COG velocity while standing on the foam surface during resting, open jaw position, clenched jaw position, chewing, and tongue positions were 1.42, 1.23, 1.10, 1.14, and 1.06 deg/s, respectively. Compared to the firm surface, the COG velocity was significantly higher on the foam surface in all five conditions (p < .001). In the comparison between the conditions, there were no significant differences in either the firm or foam surface in all five conditions (p > .05).

CONCLUSION

People with blindness behave in the same way as sighted subjects on firm and foam surfaces. However, changes in static and dynamic jaw positions do not affect postural stability among them.

Ground reaction forces during stair ascending and descending in congenitally blind and sighted individuals

BACKGROUND

Stair ascending and descending are common in daily life activities which are challenging for blind individuals. Visual information plays an important role in controlling an individual's movements. However, the relationship between visual information and stair ascending and descending is poorly understood.

OBJECTIVE

The aim of this study was to investigate how blindness alters the ground reaction force (GRF) components during ascending and descending the stairs.

METHODS

Ten individuals with congenital blindness and 10 able-bodied sighted individuals were served as experimental (EG) and control groups (CG), respectively. The GRFs were recorded during stair ascending and descending tasks using a portable 40 × 40 cm Kistler force plate which was placed on a firm stair. CG repeated the ascending/descending tasks in both open and closed-eyes conditions. For within and between groups comparisons the repeated measure ANOVA and MANOVA tests were used, respectively. The significance level was set at p < 0.05 for all comparisons.

RESULTS

In ascending task, there was not any significant between group differences on GRF components. However, closing the eyes in CG resulted in a significant decrease in some GRF components in the stair descending (p < 0.05). The GRF components of the stair descending in CG with open and closed-eyes were significantly different from those in the blind group; however, the differences were less in closed-eyes.

SIGNIFICANCE

The GRF in the stair descent was similar in both blind and sighted individuals with closed-eyes condition, that it can increase the risk of falling in blind people. As a result, the provision of tools and equipment for the blind in descent conditions is essential.

Cognitive-Motor Interference during Dual Tasks in Blind Children

The aim of the present study was to compare the dual-task (DT) performance in blind children with sighted ones while concurrently performing a motor task (upright standing) with cognitive (Letter fluency (LF) or Category fluency (CF)) tasks. The Center of pressure mean velocity (CoP_Vm) and the cognitive performances were recorded during single (ST) and DT conditions. Results showed that, for both groups, CoP_Vm values increased significantly (p < 0.05) in the DT compared to ST condition. The CoP_Vm values were significantly (p < 0.001) higher in blind children, compared to controls only in the DT-CF condition. In conclusion, balance performance of blind and typically developed children is affected by dual tasking. Interference between motor and cognitive tasks has more pronounced effects on balance performance in blind children, compared to controls. This difference was observed only when performing the CF task concurrently with the postural balance task.

The effect of occupation-based postural stability training on postural stability and occupational performance in visually impaired individuals: A randomised controlled trial

Introduction

The purpose of this research was to examine the effect of occupation-based postural stability training on occupational performance and postural stability in visually impaired individuals.

Method

The research was designed as pre-test/post-test, with two groups (study group and control group). A total of 34 individuals with visual impairment were randomly assigned to the two groups. Participants were evaluated using a sociodemographic information form, the Biodex Balance System for postural stability, the Canadian Occupational Performance Measurement for assessing performance and satisfaction of occupations and the semi-structured interview form. The control group received only postural stability training with the Biodex Balance System and the study group received individualised occupation-based postural stability training with the Biodex Balance System BBS during a 12-week intervention (24 sessions).

Results

A statistically significant difference was found between the postural stability values of the study group and the control group when looking at pre and post-training measurements ( p < 0.05). It was observed that there was an improvement in the postural stability of the participants in both groups. There was a statistically significant increase in the occupational performance and satisfaction of participants in the study group ( p < 0.01).

Conclusion

Adding person-centred, meaningful and purposeful occupations into rehabilitation programmes that use technological devices increases functionality in activities of daily living.

Changes in plantar load distribution in legally blind subjects

We investigated the impact of visual impairment on balance control. We measured the center of pressure (COP) between the two feet and plantar surface pressures on each foot in 18 normal-sighted participants and compared their data with measures from 18 legally blind participants, either acquired or congenital. Pressures were measured in open- and closed-eye conditions using a baropodometric resistive plate. In the eyes-open condition, there were no differences between the sighted and legally blind groups in COP displacement. However, participants with visual loss had significantly increased pressures in two metatarsal regions (M1 and M2 zones) of the plantar surface in both viewing conditions (p < 0.05). The differences in pressure measures between the normally sighted and legally blind groups could be attributed mainly to the subgroup of subjects with acquired impairment. Our findings suggest that subjects with visual impairment present increased metatarsal pressures (i.e. forefoot), not yet associated to anterior displacement of COP or impaired balance control.

Independent walking and balance in children with CHARGE syndrome

Children with CHARGE syndrome (CWCS) are born with multiple physical disabilities, several of which impair balance and the onset of motor milestones. Early motor development problems can include delayed independent walking, which has been found in CWCS. In addition, few studies have examined balance in CWCS and these studies have been limited in scope, necessitating a more comprehensive examination of balance in this population. Motor development occurs as a progression of stages as represented by Seefeldt’s conceptual model. As such, it is essential to examine the association of early development of foundational skills, such as balance, with the onset of motor milestones as they are building blocks to motor competence. The aims of this study are to (1) examine the differential effects of children with and without CHARGE syndrome on balance and (2) examine the association of age of walking to these balance measures. In this study, 27 CWCS and 22 children without CHARGE syndrome, aged 7 to 16 years, were assessed on four components of balance including anticipatory control, reactive postural control, sensory orientation, and dynamic gait using the shortened version of the Balance Evaluation Systems Test (mini-BESTest) and parental reported age of independent walking. Their balance and age of walking were compared to 22 typically developing peers of similar age and gender distribution. Results revealed that CWCS walked three times later than their peers without CHARGE syndrome and had significant deficits on all balance systems assessed with the largest difference occurring in anticipatory control. Anticipatory control is critically important in maintaining static and dynamic postural control. These results indicate a critical need for early functional balance training and compensatory strategies in CWCS.

Auditory cues behind congenitally blind subjects improve their balance control in bipedal upright posture

BACKGROUND

Congenitally blind subjects developed postural adaptations improving somatosensory and vestibular systems to maintain upright stability and auditory skills to orient them in environment. However, the influence of auditory cues on upright stability in congenitally blind subjects stays unknown.

RESEARCH QUESTION

The aim of this study is to define the influence of an auditory cue in congenitally blind subjects back space on their balance posture.

METHODS

Eleven sighted subjects and eleven congenitally blind subjects performed upright bipedal and unipedal quiet stances on a force plate with two conditions of auditory cue played by a loudspeaker placed 2 m behind them. Mean CoP velocity were recorded. Student test was used to compare significant difference between blind and sighted subjects bipedal and unipedal postures stability in both conditions of auditory cue.

RESULTS AND SIGNIFICANCE

Results showed that congenitally blind subjects had no significant difference in mean sway velocity compared to sighted subjects in bipedal upright posture in auditory signal condition. However, blind subjects had significant lower mean sway velocity than sighted subjects in bipedal upright posture without sound. Blind subjects had significant increased mean sway velocity during unipedal quiet standing in both auditory cue conditions (with and without sound). The results showed that congenitally blind subjects used auditory cues placed behind them in order to improve their balance control in bipedal upright posture. In this case, blind subjects could better use compensatory mechanisms to perform quiet standing as sighted subjects. Without sound or in unipedal upright posture, congenitally blind subjects probably have sensory perturbations or limitations that impose them adaptations in order to avoid falling risk. Auditory cues should be study in the aim to better understand the compensatory mechanisms used by congenitally blind subjects to perform postural balance in usual environment.

Improved balance performance accompanied by structural plasticity in blind adults after training

Postural control requires the sensory integration of visual, vestibular, and proprioceptive signals. In the absence of vision, either by blindfolding or in blind individuals, balance performance is typically poorer than with sight. Previous research has suggested that despite showing compensatory vestibular and proprioceptive processing during upright standing, balance performance in blind individuals is overall lower than in sighted controls with eyes open. The present study tested whether balance training, which places demands on vestibular and proprioceptive self-motion perception, improves balance performance in blind adults, and whether we find similar structural correlates in cortical and subcortical brain areas as have been reported in sighted individuals. Fourteen congenitally or late blind adults were randomly assigned to either a balance or a relaxation group and exercised twice a week for 12 weeks. Assessments prior to and after training included balance tests and the acquisition of T1-weighted MRI images. The blind balance group significantly improved in dynamic, static, and functional balance performance compared to the blind relaxation group. The balance performance improvement did not differ from that of age- and gender matched sighted adults after balance training. Cortical thickness increased in the left parahippocampus and decreased in the inferior insula bilaterally in the blind balance group compared to the blind relaxation group. Thickness decreases in the insula were related to improved static and functional balance. Gray matter volume was reduced in the left hippocampus proper and increased in the right subiculum in the blind balance group. The present data suggest that impaired balance performance in blind adults can be significantly improved by a training inducing plasticity in brain regions associated with vestibular and proprioceptive self-motion processing.

H-reflex modulation preceding changes in soleus EMG activity during balance perturbation

When balance is compromised, postural strategies are induced to quickly recover from the perturbation. However, neuronal mechanisms underlying these strategies are not fully understood. Here, we assessed the amplitude of the soleus (SOL) H-reflex during forward and backward tilts of the support surface during standing (n = 15 healthy participants). Electrical stimulation of the tibial nerve was applied randomly before platform tilt (control) and 0, 25, 50, 75, 100 or 200 ms after tilt onset. During backward tilt, a significant decrease in H-reflex amplitude was observed at 75, 100 and 200 ms. The onset of the decreased H-reflex amplitude significantly preceded the onset of the SOL EMG decrease (latency: 144 ± 16 ms). During forward tilt, the amplitude of the H-reflex increased at 100 and 200 ms after tilt onset. The onset of H-reflex increase did not occur significantly earlier than the onset of the SOL EMG increase (127 ± 5 ms). An important inter-subject variability was observed for the onset of H-reflex modulation with respect to EMG response for each direction of tilt, but this variability could not be explained by the subject's height. Taken together, the results establish the time course of change in SOL H-reflex excitability and its relation to the increase and decrease in SOL EMG activity during forward and backward tilts. The data presented here also suggest that balance mechanisms may differ between forward and backward tilts.

Postural control in blind individuals: A systematic review

Postural control (PC) requires the interaction of the three sensory systems for a good maintenance of the balance, and in blind people, lack of visual input can harm your PC. Thus the objective is to perform a literature review concerning role of sight in the maintenance of PC and the adaptation of brain structures when vision is absent. Studies were searched from Pubmed, and EMBASE that included individuals with congenital blindness. Articles studying person with acquired blindness or low vision was excluded from this review. 26 out of 322 articles were selected for review, and we found that 1) blind individuals exhibit PC deficits and that is compensated by the intensification of the remaining systems; 2) Neuroplastic adaptation occurs throughout the entire cerebral cortex; and 3) Sensorimotor stimulation and transcranial direct current stimulation seem to be a rehabilitation strategy. According to this review, the findings suggest that improved remaining sensations in the presence of adaptations and neuroplasticity, does not translate into better postural control performance. Regarding rehabilitation strategies, more studies are needed to show which therapeutic modality best contributes to postural control.

Postural Control in Young People with Visual Impairments and Various Risks of Falls

Introduction

Early diagnosis of postural control deficiencies facilitates implementation of an individual rehabilitation plan to prevent falls. The aim of the study was to assess the risk of falling in individuals with visual impairments, and to compare performance-based and theoretical limits of stability in subjects with various risks of falling.

Methods

The study was comprised of 23 participants with severe visual impairments. The risk of fall was assessed with the Step Test. Performance-based limits of stability were measured with the Advanced Mechanical Technology, Inc. (AMTI) platform, and theoretical limits of stability were calculated based on the height of the center of mass (COM) and maximum body sway leaning angles.

Results

COM displacement values, corresponding to performance-based limits of stability, in individuals with visual impairments whose risk of falling was classified as high were significantly lower than the theoretical values (p ≤ .05). Similar differences were not observed in participants with visual impairments whose risk of falling was assessed as low. Individuals from the low-risk group showed significantly higher values of performance-based limits of stability than the participants from the high-risk group (p ≤ .01 for medio-lateral direction and p ≤ .05 for forward-backward direction).

Discussion

Nearly half of young people with visual impairments are at increased risk of falling. Such persons showed lower performance-based limits of stability than participants with visual impairments with a low risk of falling. Performance-based limits of stability in individuals with visual impairments with a high risk of falling are lower than their theoretical limits of stability.

Implications for practitioners

The fact that nearly half of young people with visual impairments are at an increased risk of falling necessitates implementation of preventive measures in this group, as well as among individuals who are blind.

Beyond deficit or compensation: new insights on postural control after long-term total visual loss

Loss of vision is well known to affect postural control in blind subjects. This effect has classically been framed in terms of deficit or compensation depending on whether body sway increases or decreases in comparison with that of sighted subjects with the eyes open. However, studies have shown that postural responses can be modulated by the context and that changes in postural sway may not necessarily mean a worsened or improved postural control. The goal of our study was to test whether balance is affected by the context in blind subjects. Additional to the quantification of center of pressure (COP) displacement, measurements of body motion (COG) and the correspondent net neuromuscular response (COP-COG) were evaluated in anterior-posterior and medial-lateral directions. Thirty-eight completely blind and thirty-two sighted subjects participated of this study. The volunteers were asked to stand barefoot on a force platform for 60 s in two different conditions: feet apart and feet together. Sighted participants performed the tests with both the eyes open and eyes closed. Results showed that the COP-COG displacements in the blind group were greater than those of the sighted group with eyes open in almost all conditions tested, but not in eyes closed condition. However, the COP and COG results confirmed that the postural responses were context dependent. Together these results suggest that total visual loss does not just lead to a balance deficit or compensation, but to a specific postural signature that might imply in enhancing COP, COG and/or COP-COG in specific postural conditions.

Postural control in blind subjects

OBJECTIVE

To analyze postural control in acquired and congenitally blind adults.

METHODS

A total of 40 visually impaired adults participated in the research, divided into 2 groups, 20 with acquired blindness and 20 with congenital blindness - 21 males and 19 females, mean age 35.8 ± 10.8. The Brazilian version of Berg Balance Scale and the motor domain of functional independence measure were utilized.

RESULTS

On Berg Balance Scale the mean for acquired blindness was 54.0 ± 2.4 and 54.4 ± 2.5 for congenitally blind subjects; on functional independence measure the mean for acquired blind group was 87.1 ± 4.8 and 87.3 ± 2.3 for congenitally blind group.

CONCLUSION

Based upon the scale used the results suggest the ability to control posture can be developed by compensatory mechanisms and it is not affected by visual loss in congenitally and acquired blindness.

Balance Functional Assessment in People with Visual Impairment

The aims of this study were twofold: to assess the level of balance of people with visual impairment against the BOT-2 standard scores for the able-bodied, and to identify in which trials subjects had the greatest difficulties in maintaining balance with respect to the degree of vision loss and age categories. One hundred twenty-seven subjects with visual impairment aged 6–16 years, participated in the study (68 girls and 59 boys). The division for partially sighted people (61) and the blind (66) was made according to the WHO classification. Functional balance assessment was made using a balance subtest from the Bruininks-Oseretsky test. Significant relationships were noticed between age and the level of balance (χ2 = 8.35 p <0,05), as well as between the degree of vision loss and the level of balance (χ2 = 24.53 p <0,001). The level of balance of almost all blind subjects was below (20%) or well-below (60%) the average for the able-bodied. The subjects’ ability to maintain balance was not dependent on gender and was associated primarily with the degree of visual impairment and age. Partially sighted people had better balance than the blind and the decrease in visual acuity resulted in reduction of balance skills. The lowest level of balance was observed in blind students aged 7–11 years. Elaborating physical fitness improvement programs for children and adolescents with visual impairment, diversity of age, the degree of vision loss and limitations of ablility to maintain balance should be taken into account.

Influence of light touch using the fingertips on postural stability of poststroke patients

[Purpose] The purpose of this study was to investigate the influence of fingertip light touch on the postural control in poststroke patients. [Subjects] In the study, the subjects were recruited through a rehabilitation hospital, and 21 patients were screened from among 30 volunteers. [Methods] The subjects participated in an experiment that measured postural sway during the static standing posture without light touch and postural sway during the static standing posture with light touch as follows: visual information not blocked without light touch, visual information blocked without light touch, visual information blocked with light touch using fingertips, and visual information not blocked with light touch using fingertips. The measurements were performed using a force platform. The variables measured by the force platform included sway velocities of the COP in the anterior and posterior directions and, medial and lateral directions and sway velocity moments. [Results] In the results of the study, there were significant differences between the state without light touch and state with light touch in terms of the postural sway velocity and velocity moment under all conditions. The rate of decease of the sway velocity and moment velocity under the eyes closed condition were higher compared with those under the eyes open condition. [Conclusion] Through this study, we confirmed the influence of fingertip light touch on the decrease in postural sway. The results show that active light touch may be supplemental means of improving postural sway in stroke patients.

Time-interval for integration of stabilizing haptic and visual information in subjects balancing under static and dynamic conditions

Maintaining equilibrium is basically a sensorimotor integration task. The central nervous system (CNS) continually and selectively weights and rapidly integrates sensory inputs from multiple sources, and coordinates multiple outputs. The weighting process is based on the availability and accuracy of afferent signals at a given instant, on the time-period required to process each input, and possibly on the plasticity of the relevant pathways. The likelihood that sensory inflow changes while balancing under static or dynamic conditions is high, because subjects can pass from a dark to a well-lit environment or from a tactile-guided stabilization to loss of haptic inflow. This review article presents recent data on the temporal events accompanying sensory transition, on which basic information is fragmentary. The processing time from sensory shift to reaching a new steady state includes the time to (a) subtract or integrate sensory inputs; (b) move from allocentric to egocentric reference or vice versa; and (c) adjust the calibration of motor activity in time and amplitude to the new sensory set. We present examples of processes of integration of posture-stabilizing information, and of the respective sensorimotor time-intervals while allowing or occluding vision or adding or subtracting tactile information. These intervals are short, in the order of 1–2 s for different postural conditions, modalities and deliberate or passive shift. They are just longer for haptic than visual shift, just shorter on withdrawal than on addition of stabilizing input, and on deliberate than unexpected mode. The delays are the shortest (for haptic shift) in blind subjects. Since automatic balance stabilization may be vulnerable to sensory-integration delays and to interference from concurrent cognitive tasks in patients with sensorimotor problems, insight into the processing time for balance control represents a critical step in the design of new balance- and locomotion training devices.

Rapid processing of haptic cues for postural control in blind subjects

OBJECTIVES

Vision and touch rapidly lead to postural stabilization in sighted subjects. Is touch-induced stabilization more rapid in blind than in sighted subjects, owing to cross-modal reorganization of function in the blind?

METHODS

We estimated the time-period elapsing from onset of availability of haptic support to onset of lateral stabilization in a group of early- and late-onset blinds. Eleven blind (age 39.4 years±11.7SD) and eleven sighted subjects (age 30.0 years±10.0SD), standing eyes closed with feet in tandem position, touched a pad with their index finger and withdrew the finger from the pad in sequence. EMG of postural muscles and displacement of centre of foot pressure were recorded. The task was repeated fifty times, to allow statistical evaluation of the latency of EMG and sway changes following the haptic shift.

RESULTS

Steady-state sway (with or without contact with pad, no haptic shift) did not differ between blind and sighted. On adding the haptic stimulus, EMG and sway diminished in both groups, but at an earlier latency (by about 0.5 s) in the blinds (p <0.01). Latencies were still shorter in the early-than late-blinds. When the haptic stimulus was withdrawn, both groups increased EMG and sway at equally short delays.

CONCLUSIONS

Blinds are rapid in implementing adaptive postural modifications when granted an external haptic reference. Fast processing of the stabilizing haptic spatial-orientation cues may be favoured by cortical plasticity in blinds.

SIGNIFICANCE

These findings add new information to the field of sensory-guided dynamic control of equilibrium in man.

Sensorimotor posture control in the blind: superior ankle proprioceptive acuity does not compensate for vision loss

To better understand sensorimotor posture control differences between blind and sighted individuals, we examined the role of ankle joint proprioception and ankle muscle strength on postural control in healthy blind (n=13, 25-58 years) and age- and sex-matched sighted (n=15, 20-65 years) volunteers. We measured ankle joint proprioceptive acuity and isokinetic muscle strength in plantarflexion and dorsiflexion using an isokinetic dynamometer. We also assessed postural control performance during quiet bipedal stance with and without sudden postural perturbations, and during quiet unipedal stance. We found that while our blind subjects exhibited significantly better proprioceptive acuity than our sighted subjects their postural control performance was significantly poorer than that of the sighted group with eyes open, and no different from that of the sighted group with eyes closed suggesting that their superior proprioceptive acuity does not translate to improved balance control.

Static and dynamic postural control in low-vision and normal-vision adults

OBJECTIVE

This study aimed to evaluate the influence of reduced visual information on postural control by comparing low-vision and normal-vision adults in static and dynamic conditions.

METHODS

Twenty-five low-vision subjects and twenty-five normal sighted adults were evaluated for static and dynamic balance using four protocols: 1) the Modified Clinical Test of Sensory Interaction on Balance on firm and foam surfaces with eyes opened and closed; 2) Unilateral Stance with eyes opened and closed; 3) Tandem Walk; and 4) Step Up/Over.

RESULTS

The results showed that the low-vision group presented greater body sway compared with the normal vision during balance on a foam surface (p≤0.001), the Unilateral Stance test for both limbs (p≤0.001), and the Tandem Walk test. The low-vision group showed greater step width (p≤0.001) and slower gait speed (p≤0.004). In the Step Up/Over task, low-vision participants were more cautious in stepping up (right p≤0.005 and left p≤0.009) and in executing the movement (p≤0.001).

CONCLUSION

These findings suggest that visual feedback is crucial for determining balance, especially for dynamic tasks and on foam surfaces. Low-vision individuals had worse postural stability than normal-vision adults in terms of dynamic tests and balance on foam surfaces.

Análise estabilométrica pré e pós-exercícios fisioterapêuticos em crianças deficientes visuais

INTRODUÇÃO: Crianças deficientes visuais congênitas apresentam deficit de equilíbrio estático e dinâmico quando comparadas a crianças de visão normal de mesma idade. Diante da falta de visão para fornecer as informações sensoriais que permitam um feedback postural, o equilíbrio torna-se difícil, por isso a importância de estimular as vias vestibulares e proprioceptivas por meio de exercícios. A estabilometria é um método de análise do equilíbrio postural pela quantificação das oscilações do corpo, por uma plataforma cujos deslocamentos nos eixos ântero-posteriores e latero-lateral são analisados em termos do centro de pressão. OBJETIVO: Verificar o equilíbrio, por meio da estabilometria, em crianças com deficiência visual entre 5 a 13 anos pré e pós-exercícios terapêuticos. MATERIAIS E MÉTODOS: A amostra foi composta por dez crianças, duas crianças com deficiência visual total e oito crianças com deficiência visual subtotal. Após a avaliação pela estabilometria, as crianças foram submetidas a um protocolo de exercícios por um período de dois meses, e ao final foram avaliadas novamente. RESULTADOS: A média de idade foi de 8,52 (± 2,33) anos, o valor de significância encontrado para velocidade do corpo foi de p = 0,0001 e para deslocamento do corpo foi de p = 0,016, o que configura uma melhora estatisticamente significativa na velocidade de oscilação e deslocamento do corpo das crianças. CONCLUSÃO: Com base nos resultados obtidos neste estudo, pode-se comprovar que os exercícios terapêuticos propostos influenciam na melhora do equilíbrio, verificando a importância da intervenção fisioterapêutica em crianças com deficiência visual.

NEUROMUSCULAR RESPONSES OF TRAINED BALLET DANCERS TO POSTURAL PERTURBATIONS

The balance of trained ballet dancers and non-dancer controls was mechanically perturbed in order to evaluate the time of onset of muscle activation and the consistency of muscle activation. Results supported the prediction that ballet dancers have significantly faster long-latency (LL) neuromuscular responses than controls and are significantly more consistent in muscle activation. These findings indicate a superior postural control mechanism in trained dancers and may explain the ability of dancers to maintain static balances over a small base of support.

Motor imagery in blind subjects: the influence of the previous visual experience

Mental simulation of movements has been widely used to infer about representational aspects of action. On a daily basis, motor planning and execution depends crucially both upon vision and kinesthesia. What if the former is lost? In this study we investigate the physiological changes induced during a mental simulation task in subjects with early and late onset blindness, analyzing simultaneously stabilometric (body sway), electromyographic (EMG, lateral gastrocnemius) and eletrocardiographic (ECG) signals. Subjects were asked to stand up on a force platform and instructed either to: rest during 20s; count mentally from 1 to 15; imagine themselves executing a bilateral plantar flexion 15 times and execute the same movement 15 times. Discriminant analysis was employed to have access to the differences in the groups with respect to heart rate variability (HRV), EMG and body sway measurements for each condition. We found an overall correct classification of 100 and 90.9%, respectively, for the stabilometric parameters and HRV. This result was found only for the mental simulation task (p<0.05), being absent for resting, counting and executing. Previous studies have shown that motor simulation in a kinesthetic mode strongly associates with somatic and autonomic changes. In late blind subjects, however, movement simulation would tend to unfold with the use of both visual and kinesthetic representations. Thus, our results suggest that early and late blind subjects make use of distinct body representations during motor imagery.