Long-lasting reduction in postural asymmetry by prism adaptation after right brain lesion without neglect

Region-specific Effects of Transcranial Direct Current Stimulation Over Posterior Parietal Cortex and Cerebellum on Standing Postural Displacement After Prism Adaptation

Prism adaptation (PA) induces the after-effects of adapted tasks and transfers after-effects of non-adapted tasks, in which PA with pointing movements transfers to postural displacement during eyes-closed standing. However, the neural mechanisms underlying the transfer of PA after-effects on standing postural displacement remain unclear. The present study investigated the region-specific effects of transcranial direct current stimulation (tDCS) over the posterior parietal cortex (PPC) and cerebellum during prism exposure (PE) on standing postural displacement in healthy adults. Forty-two healthy young adults were grouped into pointing during PE with cathodal tDCS over the right PPC, anodal tDCS over the right cerebellum, and sham tDCS groups. They received 20 min of tDCS, during which they pointed to the visual targets while wearing prism lenses with a leftward visual shift (30 diopters) for 15 min. During the early PE, the pointing errors in the cerebellum group were significantly displaced more accurately toward the targets than those in the PPC group. However, after leftward PE, all groups had similar rightward displacements of the straight-ahead pointing with eyes closed. The PPC group only exhibited significant rightward center-of-pressure displacement during eyes-closed standing with feet-closed after leftward PE. The perception of longitudinal body axis rotation, as an indicator of the subjective body vertical axis, did not differ significantly between the pre- and post-evaluations in all groups. These results show that the PPC during PE could make an important neural contribution to inducing transfer of PA after-effect on standing postural displacement.

From real to virtual prism adaptation therapy: a systematic review on benefits and challenges of a new potential rehabilitation approach

Prism adaptation (PA) is a sensorimotor technique that has been shown to alleviate neglect symptoms. Due to its demonstrated functional effectiveness, PA has recently been implemented in virtual reality environments. However, research on virtual prism adaptation (VPA) is limited and it lacks a standardized methodological approach. It is crucial to investigate whether VPA can be effective in inducing traditional effect of PA and to have potential utility in a rehabilitation context. Clarifying this aspect would allow the use of VPA in a wider range of contexts and neurological disorders, with the additional opportunity to overcome PA traditional limits. The aim of the present study is to revise current literature on VPA in both healthy individuals and patients highlighting also its advantages and limitations. Studies performed between 2013 and 2023 and fulfilling the inclusion criteria were searched on three electronic databases, by combining the terms "Virtual prism adaptation" and "Virtual prism adaptation therapy. Out of 123 articles, only 16 met the inclusion criteria. The current literature review suggests that VPA may serve as a potentially useful tool for inducing visuomotor adaptation, with most studies conducted in healthy individuals. The high variability in the methodologies observed among studies suggests that more standardized approaches are needed to gain a deeper understanding of the mechanisms underlying adaptation and aftereffects when PA is administered in a virtual environment. Future studies should also address practical applications and clinical efficacy of VPA, particularly in patients with spatial neglect.

Effects of a visual search task in a virtual reality space with a moving background on spatial cognition and standing balance in patients with left hemiparetic stroke

We examined effects of a visual search task (VST) in virtual reality (VR) with a moving background on spatial cognition and standing balance in left hemiparetic strokes. The VST with background deviation was allocated to Case A. In Case B, the VST without the deviation was performed. As a results, in Case A, the reaction time of VST was shortened in the paretic space and ability of weight-shift to the paretic side was improved. In conclusion, the VST in the VR with a spatial manipulation may improve spatial cognition and standing balance in left hemiparetic strokes.

Effects of prismatic adaptation on balance and postural disorders in patients with chronic right stroke: protocol for a multicentre double-blind randomised sham-controlled trial

INTRODUCTION

Patients with right stroke lesion have postural and balance disorders, including weight-bearing asymmetry, more pronounced than patients with left stroke lesion. Spatial cognition disorders post-stroke, such as misperceptions of subjective straight-ahead and subjective longitudinal body axis, are suspected to be involved in these postural and balance disorders. Prismatic adaptation has showed beneficial effects to reduce visuomotor disorders but also an expansion of effects on cognitive functions, including spatial cognition. Preliminary studies with a low level of evidence have suggested positive effects of prismatic adaptation on weight-bearing asymmetry and balance after stroke. The objective is to investigate the effects of this intervention on balance but also on postural disorders, subjective straight-ahead, longitudinal body axis and autonomy in patients with chronic right stroke lesion.

METHODS AND ANALYSIS

In this multicentre randomised double-blind sham-controlled trial, we will include 28 patients aged from 18 to 80 years, with a first right supratentorial stroke lesion at chronic stage (≥12 months) and having a bearing ≥60% of body weight on the right lower limb. Participants will be randomly assigned to the experimental group (performing pointing tasks while wearing glasses shifting optical axis of 10 degrees towards the right side) or to the control group (performing the same procedure while wearing neutral glasses without optical deviation). All participants will receive a 20 min daily session for 2 weeks in addition to conventional rehabilitation. The primary outcome will be the balance measured using the Berg Balance Scale. Secondary outcomes will include weight-bearing asymmetry and parameters of body sway during static posturographic assessments, as well as lateropulsion (measured using the Scale for Contraversive Pushing), subjective straight-ahead, longitudinal body axis and autonomy (measured using the Barthel Index).

ETHICS AND DISSEMINATION

The study has been approved by the ethical review board in France. Findings will be submitted to peer-reviewed journals relative to rehabilitation or stroke.

TRIAL REGISTRATION NUMBER

NCT03154138.

The effects of repetitive neck-muscle vibration on postural disturbances after a chronic stroke

OBJECTIVE

We aimed to test a repeated program of vibration sessions of the neck muscles (rNMV) on postural disturbances and spatial perception in patients with right (RBD) versus left (LBD) vascular brain damage.

METHODS

Thirty-two chronic stroke patients (mean age 60.9±10 yrs and mean time since stroke 4.9±4 yrs), 16 RBD and 16 LBD, underwent a program of 10 sessions of NMV over two weeks. Posturography parameters (weight-bearing asymmetry (WBA), Xm, Ym, and surface), balance rating (Berg Balance Scale (BBS), Timed Up and Go (TUG)), space representation (subjective straight ahead (SSA), longitudinal body axis (LBA), subjective visual vertical (SVV)), and post-stroke deficiencies (motricity index, sensitivity, and spasticity) were tested and the data analyzed by ANOVA or a linear rank-based model, depending on whether the data were normally distributed, with lesion side and time factor (D-15, D0, D15, D21, D45).

RESULTS

The ANOVA revealed a significant interaction between lesion side and time for WBA (P<0.0001) with a significant shift towards the paretic lower limb in the RBD patients only (P=0.0001), whereas there was no effect in the LBD patients (P=0.98). Neither group showed a significant modification of spatial representation. Nonetheless, there was a significant improvement in motricity (P=0.02), TUG (P=0.0005), and BBS (P<0.0001) in both groups at the end of treatment and afterwards.

CONCLUSIONS

rNMV appeared to correct WBA in RBD patients only. This suggests that rNMV could be effective in treating sustainable imbalance due to spatial cognition disorders.

Regression of left hyperschematia after prism adaptation: A single case study

Prism adaptation (PA) is a promising treatment in the rehabilitation of post-stroke cognitive disorders such as unilateral spatial neglect or constructional deficits. Right brain damage can bring about another representational spatial disorder, termed «hyperschematia», and defined by a left-sided disproportionate expansion of drawings by copy and from memory, and by an overestimation of left lateral extent when a leftward movement is required. This case study aimed at evaluating the effect of PA induced by prismatic lenses creating a shift to the left on hyperschematia signs. A 63-year-old woman with left hyperschematia, consecutive to a right fronto-temporo-parietal hematoma, was exposed to a leftward optical deviation produced by prismatic lenses. An anatomical MRI studied topography of the brain lesion; the patient's lesion was then mapped onto tractography reconstructions of white matter pathways. Results showed that PA significantly reduced the left-sided expansion of drawing by copy and from memory, and the overestimation of left lateral extent, immediately after prism removal and 4 days later, indicating a persistent long lasting cognitive effect. MRI showed a right hemisphere disconnection of the posterior and long segments of the arcuate fasciculus, and of the inferior longitudinal and fronto-occipital fasciculi. Overall, these findings suggest that: i) PA is effective also in hyperschematia by re-orientating spatial attention towards the right side of space, with a relative rightward PA-induced unbalance, and re-setting the spatial representation to the left side of space, contralateral to the side of the lesion; ii) the left misrepresentation of lateral extent may be related to a disconnection between visual coordinates and attentional networks to the frontal lobe.

Improvement of Navigation and Representation in Virtual Reality after Prism Adaptation in Neglect Patients

Prism adaptation (PA) is responsible for an expansion of sensori-motor after-effects to cognitive domains for patients with spatial neglect. One important question is whether the cognitive after-effects induced by PA may also concern higher aspects of spatial cognition, such as navigation and topographic memory, which are critical in everyday life. The aim of this study was to assess whether multiple sessions of right PA can affect navigation and topographic memory. Seven right brain-damaged (RBD) patients with chronic neglect were included. We used a virtual supermarket named VAP-S which is an original paradigm, similar to the "shopping list test" during which patients had to purchase items from a list of eight products. Furthermore, in order to assess generalization of PA effects on constructing a spatial map from virtual information, each participant was then asked to draw the map of the virtual supermarket from memory. Regarding navigation performance, significant results were obtained: session duration reduction, fewer numbers of pauses and omissions, more items purchased on the left side and more items purchased over all. A long-lasting effect was noted, up to one month after PA. The representational task performance was also significantly increased for map drawing, with a reduction of the right shift of the symmetry axis of the map, more items drawn on the left side of maps and over all, and more items correctly located on the map. Some of these effects lasted for at least 7 days. These results suggest an expansion of PA benefit to a virtual environment. Crucially, the cognitive benefits induced by PA were noted for complex spatial cognition tasks required in everyday life such as navigation and topographic memory and this improvement was maintained for up to 1 month.