[Visual dependence after recent stroke]

Reliability and minimal detectable change of body-weight distribution and body sway between right and left brain-damaged patients at a chronic stage

PURPOSE

To assess the reliability and minimal detectable change (MDC) of weight-bearing asymmetry (WBA) and body sway (BS) during "eyes open" (EO) and "eyes closed" (EC) conditions for those with right brain damage (RBD) and left brain damage (LBD) at a chronic stage.

METHODS

Sixteen RBD and 16 LBD patients participated in two sessions within 15 days, composed of two trials of 30 s using a double force platform. Intraclass correlation coefficient (ICC_2,1), the standard error of measurement (SEM), and MDC were calculated for WBA and BS (area and velocity of sway).

RESULTS

Reliability of WBA was excellent (>0.75) except for EC for LBD patients (low SEM was found). The condition of EC was similar to or less reliable than that of EO. The MDC of WBA was 5.4 and 7.3% for LBD and RBD patients, respectively. Velocity of sway should be favored over the area of sway due to better reliability, with an MDC of 9 and 13 mm/s for RBD and LBD patients, respectively.

CONCLUSIONS

Parameters related to WBA and BS were highly reliable, without a difference between RBD and LBD patients, but less so in the condition of EC, and could be used for clinical rehabilitation and/or research.Implications for rehabilitationWeight-bearing asymmetry (WBA) and body sway (BS) are highly reliable posturography parameters.Reliability of WBA/BS is similar among right brain damaged (RBD) and left brain damaged (LBD) patients.A change of 5-7% can be interpreted as significant for WBA for chronic stroke.The minimal detectable change in measures is slightly higher for RBD patients.

Perceptual-motor styles

Even for a stereotyped task, sensorimotor behavior is generally variable due to noise, redundancy, adaptability, learning or plasticity. The sources and significance of different kinds of behavioral variability have attracted considerable attention in recent years. However, the idea that part of this variability depends on unique individual strategies has been explored to a lesser extent. In particular, the notion of style recurs infrequently in the literature on sensorimotor behavior. In general use, style refers to a distinctive manner or custom of behaving oneself or of doing something, especially one that is typical of a person, group of people, place, context, or period. The application of the term to the domain of perceptual and motor phenomenology opens new perspectives on the nature of behavioral variability, perspectives that are complementary to those typically considered in the studies of sensorimotor variability. In particular, the concept of style may help toward the development of personalised physiology and medicine by providing markers of individual behaviour and response to different stimuli or treatments. Here, we cover some potential applications of the concept of perceptual-motor style to different areas of neuroscience, both in the healthy and the diseased. We prefer to be as general as possible in the types of applications we consider, even at the expense of running the risk of encompassing loosely related studies, given the relative novelty of the introduction of the term perceptual-motor style in neurosciences.

Effect of optokinetic stimulation on weight-bearing shift in standing and sitting positions in stroke patients

BACKGROUND

Patients with hemiplegia after stroke tend to bear weight on the non-paretic side and exhibit large postural sway during static standing and walking, which may increase their risk of falls. Improvement of the sitting posture balance in the early phase of rehabilitation by adjusting weight-bearing would minimize the risk of falls as early rehabilitation reportedly improves walking ability and prevents falls in later phases of rehabilitation or at discharge.

AIM

This study aimed to evaluate the effect of optokinetic stimulation (OKS) on shift of the weight-bearing (displacement of the center of pressure [CoP]) in patients with hemiplegia who are incapable of independent standing.

DESIGN

Quasi-experimental, cross-sectional study.

SETTING

Rehabilitation hospital.

POPULATION

Patients with hemiplegia in the subacute phase after stroke (N.=37).

METHODS

Standing and sitting balance tests were performed during OKS projected onto a screen. For OKS, a pattern of random dots was presented, which continuously moved in horizontal or torsional directions during both static standing and sitting conditions. Postural sway was assessed during standing and sitting by measuring the sway path, sway area, sway velocity, and mean displacement of CoP. The magnitude of the lateral change in CoP as an indicator of the weight-bearing shift was evaluated by subtraction of the mean CoP of the right-left axis component in the stationary condition from the mean CoP sway during OKS.

RESULTS

OKS induced a unilateral change of the mean CoP position in patients during both, sitting and static standing, indicating that OKS can shift the weight-bearing in patients after stroke, irrespective of the posture condition. Moreover, the same OKS approach evoked an analogous shift in patients with more severe symptoms, with impairment in independent standing.

CONCLUSIONS

OKS could induce a significant shift in weight balance in patients with hemiplegia after stroke who are incapable of independent standing, suggesting that the OKS approach can be applied to a broader spectrum of patients, including those with more severe symptoms.

CLINICAL REHABILITATION IMPACT

OKS approach would improve exercise training in the early phase of rehabilitation of patients with hemiplegia after stroke.

Functional Neuroanatomy of Vertical Visual Perception in Humans

Vertical representation is central to posture control, as well as to spatial perception and navigation. This representation has been studied for a long time in patients with vestibular disorders and more recently in patients with hemispheric damage, in particular in those with right lesions causing spatial or postural deficits. The aim of the study was to determine the brain areas involved in the visual perception of the vertical. Sixteen right-handed healthy participants were evaluated using fMRI while they were judging the verticality of lines or, in a control task, the color of the same lines. The brain bases of the vertical perception proved to involve a bilateral temporo-occipital and parieto-occipital cortical network, with a right dominance tendency, associated with cerebellar and brainstem areas. Consistent with the outcomes of neuroanatomical studies in stroke patients, The data of this original fMRI study in healthy subjects provides new insights into brain networks associated with vertical perception which is typically impaired in both vestibular and spatial neglect patients. Interestingly, these networks include not only brain areas associated with postural control but also areas implied in body representation.

Effects of continuous visual feedback during sitting balance training in chronic stroke survivors

BACKGROUND

Postural control deficits are common in stroke survivors and often the rehabilitation programs include balance training based on visual feedback to improve the control of body position or of the voluntary shift of body weight in space. In the present work, a group of chronic stroke survivors, while sitting on a force plate, exercised the ability to control their Center of Pressure with a training based on continuous visual feedback. The goal of this study was to test if and to what extent chronic stroke survivors were able to learn the task and transfer the learned ability to a condition without visual feedback and to directions and displacement amplitudes different from those experienced during training.

METHODS

Eleven chronic stroke survivors (5 Male - 6 Female, age: 59.72 ± 12.84 years) participated in this study. Subjects were seated on a stool positioned on top of a custom-built force platform. Their Center of Pressure positions were mapped to the coordinate of a cursor on a computer monitor. During training, the cursor position was always displayed and the subjects were to reach targets by shifting their Center of Pressure by moving their trunk. Pre and post-training subjects were required to reach without visual feedback of the cursor the training targets as well as other targets positioned in different directions and displacement amplitudes.

RESULTS

During training, most stroke survivors were able to perform the required task and to improve their performance in terms of duration, smoothness, and movement extent, although not in terms of movement direction. However, when we removed the visual feedback, most of them had no improvement with respect to their pre-training performance.

CONCLUSIONS

This study suggests that postural training based exclusively on continuous visual feedback can provide limited benefits for stroke survivors, if administered alone. However, the positive gains observed during training justify the integration of this technology-based protocol in a well-structured and personalized physiotherapy training, where the combination of the two approaches may lead to functional recovery.

Rod and frame test and posture under optokinetic stimulation used to explore two complementary aspects of the visual influence in postural control after stroke

BACKGROUND

Balance rehabilitation should consider individual comportments according to visual input (VI). Indeed, visual dependence (VD), defined as the predominance given to the VI whatever the circumstances, frequent after stroke it could disturb balance. Because the term VD is a bit restrictive and cannot be deduced from clinical tests, the term visual sensitivity (VS) is preferred here.

HYPOTHESIS

VI could have different influence depending on the task for a given individual.

METHODS

We retrospectively compared 2 VS tests routinely used: the rod and frame test (RFT) and optokinetic stimulation (OKS). In RFT, VS was defined by a misperception of the visual verticality induced by a tilted frame (VS RFT) and in OKS by tilted sitting posture induced by rotational OKS (VS OKS). We studied the relations between VS RFT and VS OKS.

RESULTS

We analysed data for 84 patients, mean age 55±10years, 45±30days after stroke. Scores for both tests were correlated with autonomy measured by the functional independence measure (r=-0.3, p=0.01 and r=-0.2, p=0.02). VS OKS score was also correlated with balance measured by the postural assessment scale for stroke (r=-0.3, p=0.03). VS RFT score was not correlated with VS OKS score (p=0.4, r=0.04).

DISCUSSION - CONCLUSION

A patient may display VS for one test without sensitivity for the other because these tests investigate different neural organisation - perception for RFT or action for OKS. Their relation to balance disorders should be further investigated to build individualized rehabilitation programs.

Role of proprioceptive information to control balance during gait in healthy and hemiparetic individuals

Proprioceptive information is important for balance control yet little is known about how it is used during gait or how a stroke affects its use. The aim of this study was to evaluate the role of proprioception in controlling balance during gait in healthy participants and after stroke. Twelve healthy and 9 hemiparetic participants walked on an instrumented treadmill in a fully lit room, while whole-body, three-dimensional kinematics were quantified. Vibration was applied continuously or during the stance phase only, on the posterior neck muscles and triceps surae tendon on the non-dominant/paretic side. Difficulty in maintaining dynamic and postural balance was evaluated using stabilizing and destabilizing forces, respectively. Continuous and stance phase vibration of the triceps surae reduced the difficulty in maintaining both dynamic and postural balance in healthy participants (p<.05), with a greater distance between the center of pressure and the limit of the potential base of support, a more backward body position, and no change in spatio-temporal gait parameters. No effect of neck muscle vibration was observed on balance (p=.63 and above). None of the vibration conditions affected balance or gait parameters among stroke participants. The results confirmed that proprioceptive information was not used to control balance during gait in stroke participants. The importance of proprioceptive information may depend on other factors such as walking and visual conditions. Changes in sensory integration ability likely explain the results after stroke. Further study is needed to understand the integration of proprioceptive and visual information to control balance during gait after stroke.

Sensory reweighting in controls and stroke patients

OBJECTIVE

To test sensitivity to proprioceptive, vestibular and visual stimulations of stroke patients with regard to balance.

METHOD

The postural control of 20 hemiparetic patients after a single hemispheric stroke that had occurred at least 6 months before the study along with 20 controls was probed with vibration, optokinetic, and vestibular galvanic stimulations. Balance was assessed using a force platform (PF) with two miniature inertial sensors placed on the head (C1) and the trunk (C2) under each sensory condition and measured by three composite scores as the mean displacement of the body (PF, C1, C2) during the stimulation. A subject with a composite score greater than the 75th percentile of the composite scores found in the control subjects was arbitrarily considered to be sensitive to that stimulation.

RESULTS

Both control and stroke patients showed large inter-individual variations in response to the three types of sensory stimulation. Among the hemiparetic patients, nearly 65% were sensitive to the optokinetic stimulation, 60% to the galvanic stimulation and 65% to the vibration stimulation. In contrast to the control group, all the hemiparetic subjects were sensitive to at least one type of stimulation.

CONCLUSION

Stroke patients are highly dependent on visual, proprioceptive and vestibular information in order to control their standing posture and individually differ in their relative sensitivity to each type of sensory stimulation.

SIGNIFICANCE

Contrarily to what one might suppose, the increased visual dependence manifested by stroke patients does not necessarily entail any neglect of proprioceptive and vestibular information.