Difference between voluntary control and conscious balance processing during quiet standing.

The mechanism by which postural threat induced by standing at a high height causes a decrease in the amplitude and an increase in the frequency of postural sway might involve voluntary control (VC) to avoid swaying, rather than conscious balance processing, in which postural threat directs conscious balance processing. This study aimed to clarify the differences between VC and conscious balance processing during quiet standing. Twenty-seven healthy young adults were instructed to stand with their feet placed together and keep their eyes open. The standing task was performed under three standing conditions: relaxed, VC, and high-conscious movement processing (high-CMP). The center of pressure in the anteroposterior (AP) and mediolateral (ML) directions was measured using a stabilometer to assess differences in postural control. The results indicated that the mean power frequency (MPF) ML and high frequency (HF) ML were higher in the VC condition than in the high-CMP condition. In the VC and high-CMP conditions, compared with the relaxed condition, MPF AP was higher, whereas the root mean square AP and low frequency AP were lower. These results show that the sway amplitude is lower, and the frequency is higher in both the VC and high-CMP conditions compared with those in the relaxed condition; however, the frequency is higher in the VC condition than in the high-CMP condition, suggesting that the VC condition is similar to postural control under the postural threat condition.

Effects of postural-control training with different sensory reweightings in a patient with body lateropulsion: a single-subject design study.

INTRODUCTION: Body lateropulsion (BL) is an active lateral tilt of the body during standing or walking that is thought to be affected by a lesion of the vestibulospinal tract (VST) and the subjective visual vertical (SVV) tilt. Interventions for BL have not been established. OBJECTIVE: We examined the effects of postural-control training with different sensory reweighting on standing postural control in a patient with BL. METHODS: The patient had BL to the left when standing or walking due to a left-side medullary and cerebellar infarct. This study was a single-subject A-B design with follow-up: Phase A was postural-control training with visual feedback; phase B provided reweighting plantar somatosensory information. Postural control, VST excitability, and SVV were measured. RESULTS: At baseline and phase A, the patient could not stand with eyes-closed on a rubber mat, but became able to stand in phase B. The mediolateral center of pressure (COP) position did not change significantly, but the COP velocity decreased significantly during phase B and the follow-up on the firm surface. VST excitability was lower on the BL versus the non-BL side, and the SVV deviated to the right throughout the study. CONCLUSION: Postural-control training with reweighting somatosensory information might improve postural control in a patient with BL.

Relationships between changes in lateral vestibulospinal tract excitability and postural control by dynamic balance intervention in healthy individuals: A preliminary study.

Introduction: We conducted dynamic balance or static intervention on healthy young adults to examine the changes in lateral vestibulospinal tract (LVST) excitability and postural control that ensued following dynamic balance intervention and to investigate the correlation between these changes. Methods: Twenty-eight healthy young adults were randomly assigned to either the dynamic balance group or the control group. They performed either a dynamic balance or static intervention for 10 trials of 30 s each and were assessed for head jerks during the intervention to confirm adaptation to the intervention. The dynamic balance intervention consisted of maintaining balance on a horizontally unstable surface, whereas the control intervention involved standing in the same foot position as the dynamic balance intervention on a stable surface while completing a maze task. LVST excitability and postural stability were assessed before and after the interventions. LVST excitability was assessed as the change rate in the soleus H-reflex amplitude with galvanic vestibular stimulation (GVSH). The velocity and area of the center of pressure (COP) were examined in the eyes closed/foam rubber condition. Results: No significant main and interaction effects (task, time) were observed for GVSH and COP variables. In the dynamic balance intervention, head jerk significantly decreased, and GVSH-change and changes in head jerk and COP area were significantly negatively correlated. Discussion: The LVST excitability change for the dynamic balance intervention varied among the participants, although increased LVST excitability may have been related to increased postural stability.

Changes in Standing Postural Control Ability in a Case of Spinocerebellar Ataxia Type 31 With Physical Therapy Focusing on the Center of Gravity Sway Variables and Lower Leg Muscle Activity.

Spinocerebellar degeneration (SCD) is a progressive disease characterized by cerebellar ataxia or the posterior spinal cord. Among these, spinocerebellar ataxia type 31 (SCA31) is genetically more common in the Japanese population and is characterized by pure ataxia, resulting in severe disturbances in postural balance, with common falls. Therefore, rehabilitation is important to improve postural balance. Light touch is a known method of reducing postural sway, which acts with the light touching of an object with the body. We herein present a case of a patient with SCA31 who was trained in a standing position by lightly touching the back of the body to a wall surface. Dynamic interarticular coordination exercises were also performed as part of the rehabilitation program. As a result, even in the progressive SCA31, improvements in standing postural balance and activities of daily living contributed to improvements in the patient's postural balance. We followed the progress of postural control ability using the center of gravity sway measurement and electromyography and described some interesting characteristics of the patient's postural control ability in this report.

Characteristics of postural control during fixed light-touch and interpersonal light-touch contact and the involvement of interpersonal postural coordination.

Haptic feedback by light touch with a fingertip influences the postural control of the human body by postural orientation. Postural control might therefore differ depending on the characteristics of the contacting object. The main experimental targets of contact have been a fixed object (fixed light touch: FLT) and an individual (interpersonal light touch: ILT), but the postural control characteristics of FLT and ILT have not been directly compared within the same study. Nor has there been a study comparing frequency characteristics in these conditions. We hypothesized that (1) the frequency of postural sway would be higher in FLT and that no such change would be observed in ILT, and (2) the interpersonal postural coordination that is specific to ILT, i.e., sway that resembles the other person's sway, would be observed in the low-frequency component (≤0.4 Hz) rather than the high-frequency component (>0.4 Hz). We applied a closed-eyes tandem stance by adult subjects as the standard condition, and the center of pressure was measured when they performed four standing conditions: no-touch, FLT, stable ILT with a bipedal partner, and unstable ILT with a tandem partner. The results demonstrated that the FLT condition and both the stable and unstable ILT conditions also stabilized the posture, but the stability was superior in the FLT condition. Further, the difference in postural stability depending on the axis is not clear in any conditions for velocity, whereas for amplitude, stabilization by contact is more easily captured in the medio-lateral (ML) axis than in the anterior-posterior (AP) axis. The mean power frequency (MPF) in the FLT condition was higher than the no-touch condition, and the stable ILT condition in the ML axis and was higher than any other conditions in the AP axis. Moreover, the stable ILT condition in both axes was not significantly different from the no-touch condition. The unstable ILT condition in the AP axis was also not significantly different, though the ML axis was higher than the no-touch condition. The interpersonal postural coordination in both the stable and unstable ILT conditions was observed in the low-frequency component (except for the ML axis of the unstable ILT condition) and not in the high-frequency component. These results support our hypotheses and suggest that although FLT and ILT exert effects on reducing postural sway to some certain extent, in actuality, these conditions result in different postural controls in the frequency domain due to postural coordination based on the low-frequency component.

Reliability and laterality of the soleus H-reflex following galvanic vestibular stimulation in healthy individuals.

The vestibulospinal tract (VST) plays an important role in the control of the ipsilateral antigravity muscles, and the balance of left and right VST excitability is important in human postural control. A method for measuring VST excitability is the application of galvanic vestibular stimulation (GVS) before tibial nerve stimulation that evokes the soleus H-reflex; the change rate of the H-reflex amplitude is then evaluated. Assessments of VST excitability and the left and right balance could be useful when determining the pathology for interventions in postural control impairments. However, the reliability and laterality of this assessment have not been clarified, nor has its relationship to postural control. We investigated the reliability, laterality and standing postural control in relation to the degree of facilitation of the H-reflex following GVS in 15 healthy adults. The assessments were performed in two sessions, one each for the left- and right-sides, in random order. The inter-session reliability of the short-interval assessments of an increase in the H-reflex following GVS on both sides were sufficient. The degree of H-reflex facilitation by GVS showed no significant difference between the left- and right-sides in any session. There was a moderate positive correlation between the mediolateral position of the center of pressure in the eyes-closed standing on foam condition and the left/right ratio of the degree of increased H-reflex in the first-session. We concluded that this method for evaluating the increase in the soleus H-reflex following GVS has high inter-session reliability in the short-interval that did not differ between sides.

Posture influences on vestibulospinal tract excitability.

The human vestibulospinal tract has important roles in postural control, but it has been unknown whether vestibulospinal tract excitability is influenced by the body's postures. We investigated whether postures influence the vestibulospinal tract excitability by a neurophysiological method, i.e., applying galvanic vestibular stimulation (GVS) 100 ms before tibial nerve stimulation evoking the soleus H-reflex. GVS is a percutaneous stimulation, and it has not been clarified how the cutaneous input from GVS influences the facilitation effect of cathodal GVS on the soleus H-reflex amplitude. In Experiment 1, we evaluated the effects of GVS on the soleus H-reflex amplitude of subjects in the prone, supine, and sitting positions in random order to clarify the differences in the GVS effects among these postures. In Experiment 2, to determine whether the effects of GVS in the supine and sitting positions are due solely to cutaneous input from GVS, we provided GVS and cutaneous stimulations as conditioning stimuli and compared the effects in both postures. Interaction effects between postures and stimulus conditions were observed in both experiments. The facilitation rate of the maximum H-reflex amplitude by GVS in the sitting position was significantly higher than those in the prone and supine positions (Experiment 1). The facilitation rate of GVS was significantly larger than the cutaneous stimulation only in the sitting position (Experiment 2). These results indicate that vestibulospinal tract excitability may be higher in the sitting position than in either lying position (prone and supine), due mainly to the increased need for postural control.

Standing postural stability during galvanic vestibular stimulation is associated with the motor function of the hemiplegic lower extremity post-stroke.

Background: The vestibular system is profoundly involved in standing postural stability. Patients with post-stroke hemiparesis have poor postural control function; nevertheless, it is unclear as to how the vestibular system affects postural control after stroke.Objectives: The purpose of this study was to quantitatively evaluate the relationship between galvanic whole-body sway responses and motor function of the hemiplegic lower extremity post-stroke.Methods: Thirty stroke patients and 49 healthy controls underwent standing body sway tests to examine postural control function during vestibular stimulation. Postural stabilization was measured using a C7-mounted accelerometer during galvanic vestibular stimulation. Postural stability was assessed during stimulation while quietly standing with eyes closed. For the stroke group, lower extremity function was measured using the Fugl-Meyer Assessment scale (FMA-LE).Results: The standing body sway test scores during stimulation were lower in the stroke group than the control group (p = .010). In the stroke group, correlation analysis demonstrated that the standing body sway response score was significantly associated with the FMA-LE (r = 0.374, p = .021).Conclusions: Motor dysfunction directly causes standing postural instability during vestibular stimulation, even though sensory information suggests normal peripheral vestibular function. Therefore, motor dysfunction of the hemiplegic lower extremity might lead to inhibition of normal standing postural stability.

Transient Effects of Gaze Stability Exercises on Postural Stability in Patients With Posterior Circulation Stroke.

The authors sought to investigate if short-term gaze stability exercises have an effect on postural stability of dynamic standing during neck movement in patients with posterior circulation stroke (PCS). Patients in both PCS and non-PCS groups were assigned to either an intervention or control group. The intervention group performed the gaze stability exercises for 10 min while the control group was merely resting. The center of pressure velocity was calculated to evaluate the postural stability. After intervention, PCS and non-PCS showed a significant reduction in center of pressure velocity during dynamic standing with eyes closed condition, and the PCS group showed a significant improvement in eye-opened condition. This study indicated that gaze stability exercises improve PCS patients' postural control, especially during dynamic standing.

Poor gait performance is influenced with decreased vestibulo-ocular reflex in poststroke patients.

The vestibulo-ocular reflex (VOR) exerts a significant influence on gait performance. Therefore, a decrease in VOR function could worsen gait impairments in patients with poststroke hemiparesis. The effects of decreased VOR function on gait performance could be further exacerbated by aging-related physical weakness and impaired motor function of the hemiparetic lower limb. The aim of our study was to evaluate the possible synergistic effect of aging and impairment in lower extremity function and the VOR on walking ability of poststroke hemiplegic patients. The VOR was evaluated, using the gaze-stabilization test (GST), in 75 patients with a poststroke hemiplegia. Lower extremity function was assessed using the Fugl-Meyer assessment (FMA-LE). Gait performance was evaluated using the 10-m walking test, the timed up-and-go, and the dynamic gait index (DGI). The relationships between gait performance and age, FMA-LE and GST, as well as whether age, FMA-LE, and/or GST were significant predictors of gait performance were evaluated. The 10-m walking test, timed up-and-go and DGI were significantly correlated to the FMA-LE and GST (P<0.05). On stepwise multiple regression analysis, the GST remained a significant predictor of the DGI (P<0.001). The present study indicates that decreased VOR function after stroke contributes to impairments in gait both in simple and in dual-task walking tests.

Effects of vestibular rehabilitation on gait performance in poststroke patients: a pilot randomized controlled trial.

The effects of vestibular rehabilitation on poststroke patients are unknown. This study aimed to investigate whether or not vestibular rehabilitation would improve both the vestibulo-ocular reflex and gait performance of patients with poststroke hemiparesis. Twenty-eight patients with stroke were assigned randomly to either an experimental group (N=14) or a control group (N=14). The experimental group performed the conventional physical therapy for 40 min and vestibular rehabilitation for 20 min, as a 60 min session, during the first 3 weeks and then completed only the conventional intervention for 60 min for the following 3 weeks. The control group performed only the 60 min conventional physical therapy for 6 weeks. Both groups were measured using the gaze stabilization test, the 10 m walking test, the timed up and go test, and the dynamic gait index. Patients were assessed at baseline, and at 3 and 6 weeks. Although the control group showed no significant difference in any outcome measures, the experimental group showed an improvement in gaze stabilization test scoring, which increased significantly after 3 weeks compared with the baseline (P=0.030). The dynamic gait index was also significantly increased after 3 and 6 weeks compared with the baseline (P=0.049 and 0.024, respectively). This study indicated that vestibular rehabilitation might improve poststroke patients' vestibulo-ocular reflex. Moreover, patients might show improved gait performance at least up to 3 weeks after the vestibular intervention by the sensory reweight to coordinate vestibular input.

EEG frequency analysis of cortical brain activities induced by effect of light touch.

In human postural control, touching a fingertip to a stable object with a slight force (<1 N) reduces postural sway independent of mechanical support, which is referred to as the effect of light touch (LT effect). The LT effect is achieved by the spatial orientation according to haptic feedback acquired from an external spatial reference. However, the neural mechanism of the LT effect is incompletely understood. Therefore, the purpose of this study was to employ EEG frequency analysis to investigate the cortical brain activity associated with the LT effect when attentional focus was strictly controlled with the eyes closed during standing (i.e., control, fixed-point touch, sway-referenced touch, and only fingertip attention). We used EEG to measure low-alpha (about 8-10 Hz) and high-alpha rhythm (about 10-12 Hz) task-related power decrease/increase (TRPD/TRPI). The LT effect was apparent only when the subject acquired the stable external spatial reference (i.e., fixed-point touch). Furthermore, the LT-specific effect increased the high-alpha TRPD of two electrodes (C3, P3), which were mainly projected from cortical brain activities of the left primary sensorimotor cortex area and left posterior parietal cortex area. Furthermore, there was a negative correlation between the LT effect and increased TRPD of C3. In contrast, the LT effect correlated positively with increased TRPD of P3. These results suggest that central and parietal high-alpha TRPD of the contralateral hemisphere reflects the sensorimotor information processing and sensory integration for the LT effect. These novel findings reveal a partial contribution of a cortical neural mechanism for the LT effect.

Tactile localization training for pain, sensory disturbance, and distorted body image: a case study of complex regional pain syndrome.

This report presents a case of complex regional pain syndrome. The patient presented with severe pain, sensory disturbance, and distorted body image at the site of initial injury and other body sites. Tactile localization training (TLT) at only the site of initial injury decreased severe pain at the site of initial injury and the secondary affected sites, whereas TLT at secondary affected sites had no effect. These results highlighted the importance of assessing changes in patients' pain processes to determine the part of the body where TLT should be applied.

Effects of voluntary and automatic control of center of pressure sway during quiet standing.

The authors investigated the effects of voluntary and automatic control on the spatial variables (envelope area, maximal amplitude, and root mean square [RMS]) of center of pressure (COP) displacement during quiet standing and identified differences in their postural control strategies (mean velocity [MV], mean power frequency [MPF], and power density). COP data were recorded under relaxed (experimental control), still (voluntary control), and dual (automatic control) conditions. RMS was significantly lower in the still and dual conditions than in the relaxed condition. MV, MPF, and power density were significantly higher in the still condition than in the dual condition. These results indicate that both voluntary and automatic control decrease the spatial variables of COP displacement; however, their postural control strategies are different.

Negative body image associated with changes in the visual body appearance increases pain perception.

Changing the visual body appearance by use of as virtual reality system, funny mirror, or binocular glasses has been reported to be helpful in rehabilitation of pain. However, there are interindividual differences in the analgesic effect of changing the visual body image. We hypothesized that a negative body image associated with changing the visual body appearance causes interindividual differences in the analgesic effect although the relationship between the visual body appearance and analgesic effect has not been clarified. We investigated whether a negative body image associated with changes in the visual body appearance increased pain. Twenty-five healthy individuals participated in this study. To evoke a negative body image, we applied the method of rubber hand illusion. We created an "injured rubber hand" to evoke unpleasantness associated with pain, a "hairy rubber hand" to evoke unpleasantness associated with embarrassment, and a "twisted rubber hand" to evoke unpleasantness associated with deviation from the concept of normality. We also created a "normal rubber hand" as a control. The pain threshold was measured while the participant observed the rubber hand using a device that measured pain caused by thermal stimuli. Body ownership experiences were elicited by observation of the injured rubber hand and hairy rubber hand as well as the normal rubber hand. Participants felt more unpleasantness by observing the injured rubber hand and hairy rubber hand than the normal rubber hand and twisted rubber hand (p<0.001). The pain threshold was lower under the injured rubber hand condition than with the other conditions (p<0.001). We conclude that a negative body appearance associated with pain can increase pain sensitivity.

Factors associated with the modulation of pain by visual distortion of body size.

Modulation of pain using visual distortion of body size (VDBS) has been the subject of various reports. However, the mechanism underlying the effect of VDBS on pain has been less often studied. In the present study, factors associated with modulation of pain threshold by VDBS were investigated. Visual feedback in the form of a magnified image of the hand was provided to 44 healthy adults to examine changes in pain. In participants with a higher pain threshold when visual feedback of a magnified image of the hand was provided, the two-point discrimination threshold decreased. In contrast, participants with a lower pain threshold with visual feedback of a magnified image of the hand experienced unpleasant emotions toward the magnified image of the hand. Interestingly, this emotional reaction was strongly associated with negative body consciousness in several subjects. These data suggested an analgesic effect of visual feedback in the form of a magnified image of the hand is only when tactile perception is vivid and the emotional reaction toward the magnified image is moderate. The results also suggested that negative body consciousness is important for the modulation of pain using VDBS.

Changes in electroencephalographic activity during observation, preparation, and execution of a motor learning task.

This study aimed to compare electroencephalographic (EEG) activity between high- and low-motor learning groups (n = 10 each) during observation of, preparation for, and execution of a motor learning task. The subjects performed a ball rotation task in which two balls were rotated clockwise with the right hand. Each trial started with a rest period (5 s), subjects then observed the task action on a computer screen (30 s), this was followed by another rest (5 s), preparation for performing the action (5 s), and finally action execution (30 s); five trials were performed. The number of rotations during execution and EEG activities during observation, preparation, and execution were recorded. The EEG data of the high-motor learning group were compared with those of the low-motor learning group and were analyzed using exact low-resolution electromagnetic tomography (eLORETA). The left sensorimotor and parietal areas of the high-motor learning group showed a greater decrease in the alpha-2 (10.5-12.0 Hz) and beta-2 (18.5-21.0 Hz) rhythms than those of the low-motor learning group during all three phases of the trials. The study results suggest that the decreases in the alpha-2 and beta-2 rhythms in these areas during observation, preparation, and execution are associated with motor skill improvement.

Effect of a plantar perceptual learning task on walking stability in the elderly: a randomized controlled trial.

OBJECTIVE: To determine whether the plantar perceptual learning task, using a hardness discrimination training, efficiently improves walking stability in the elderly. DESIGN: A randomized controlled trial. SETTING: Elder day-care center. PARTICIPANTS: Eighty-six elderly people (73.84 SD 5.98 years) who went to an elder day-care center were randomly assigned evenly to either an intervention or a control group. INTERVENTION: The intervention group performed a task to discriminate hardness differences while standing on sponge mats of different levels of hardness. The control group underwent the same task except that they were not instructed to discriminate hardness levels of the mats. The tasks were carried out over a four-week period for 10 days for both groups. OUTCOME MEASURES: Outcome was assessed by determining root mean squares of trunk acceleration during walking. RESULTS: Plantar perception was significantly improved in the intervention group after training (F = 26.24, p < 0.01). In addition, changes in root mean square values of acceleration were significantly greater after training in the intervention group (medial-lateral, 0.36 SD 0.26; vertical, 0.32 SD 0.24; anterio-posterior, 0.26 SD 0.24) than in the control group (medial-lateral, 0.14 SD 0.28, vertical, 0.16 SD 0.35, anterio-posterior, 0.12 SD 0.29) (p < 0.05). Changes in walking speed were not significantly different (p = 0.13) between the intervention (0.06 SD 0.13) and control groups (0.02 SD 0.14). CONCLUSION: The plantar perceptual learning task might efficiently stabilize postural control during walking in the elderly.