Correlation between changes in functional connectivity in the dorsal attention network and the after-effects induced by prism adaptation in healthy humans: A dataset of resting-state fMRI and pointing after prism adaptation

Non-invasive Brain Stimulation and Prism Adaptation in Art Constructive Errors in Painting

Introduction

This study aimed to investigate the influence of neglect and the effect of prism adaptation (PA) combined with continuous Theta-burst transcranial magnetic stimulation (cTBS) on the art constructive errors in painting rehabilitation of stroke patients with neglect.

Methods

Fourteen patients with neglect and art constructive errors in painting secondary to stroke were randomly assigned to the rehabilitation group and received PA combined with the inhibitory protocol of cTBS over the intact parietal cortex; the control group received PA combined with sham cTBS for two weeks in ten daily sessions. Patients were assessed for art constructive errors in painting in figure copying test (FCT), and coloring test (CT) before and after the intervention. Art constructive errors in painting were classified into omission, deformation, size, neglect of warm colors, and perseveration of errors. Neglect was evaluated using the line bisection task (LBT), figure copying test (FCT), and coloring test (CT).

Results

All patients showed a significant improvement in art constructive errors in painting (measured using the pattern of painting' errors in FCT and CT), and neglect (measured using LBT, FCT, and CT) (P<0.05). Omission, neglect of warm colors, and deformation were the most frequent errors.

Conclusion

Neglect and rehabilitation influence the painting system in stroke patients. Both approaches improved art constructive errors in painting and neglect symptoms.

Neural correlates of spatial attention bias: Changes in functional connectivity in attention networks associated with tDCS

The prevailing theory concerning the pathophysiology of unilateral spatial neglect is that it is caused by an interhemispheric imbalance in attention networks. Previous studies have demonstrated that repetitive transcranial magnetic stimulation or transcranial direct current stimulation (tDCS) delivered over the right posterior parietal cortex can induce transitory neglect-like deficits in healthy individuals. We examined whether right cathodal and left anodal tDCS delivered over the posterior parietal cortex could produce neglect-like deficits and change the resting-state functional connectivity (rsFC) of attention networks. We found that the reaction time for targets in the left hemifield was significantly prolonged during two different types of visual search tasks, and rsFC of the attention networks was altered by tDCS. Furthermore, the change in the reaction times for the left visual target in the two different tasks significantly correlated with the change in the rsFC of either the right dorsal attention network (DAN) or right ventral attention network (VAN) based on the tasks. These results suggest that tDCS delivered to the posterior parietal cortex bilaterally induced neglect-like deficits by altering the connectivity of the attentional networks through excitability changes in the cortical area under the electrode. The results of this study are consistent with the hypothesis that the cause of neglect is the interhemispheric imbalance of attention networks. This is the first study to demonstrate that local cortical stimulation can induce changes not only in the local brain function but also in the cortical networks in healthy individuals.

Neural Mechanisms of Prism Adaptation in Healthy Adults and Individuals with Spatial Neglect after Unilateral Stroke: A Review of fMRI Studies

Functional disability due to spatial neglect hinders recovery in up to 30% of stroke survivors. Prism adaptation treatment (PAT) may alleviate the disabling consequences of spatial neglect, but we do not yet know why some individuals show much better outcomes following PAT than others. The goal of this scoping review and meta-analysis was to investigate the neural mechanisms underlying prism adaptation (PA). We conducted both quantitative and qualitative analyses across fMRI studies investigating brain activity before, during, and after PA, in healthy individuals and patients with right or left brain damage (RBD or LBD) due to stroke. In healthy adults, PA was linked with activity in posterior parietal and cerebellar clusters, reduced bilateral parieto-frontal connectivity, and increased fronto-limbic and sensorimotor network connectivity. In contrast, RBD individuals with spatial neglect relied on different circuits, including an activity cluster in the intact left occipital cortex. This finding is consistent with a shift in hemispheric dominance in spatial processing to the left hemisphere. However, more studies are needed to clarify the contribution of lesion location and load on the circuits involved in PA after unilateral brain damage. Future studies are also needed to clarify the relationship of decreasing resting state functional connectivity (rsFC) to visuomotor function.

The role of the right posterior parietal cortex in prism adaptation and its aftereffects

Adaptation to optical prisms (Prismatic Adaptation, PA) displacing the visual scene laterally, on one side of visual space, is both a procedure for investigating visuo-motor plasticity and a powerful tool for the rehabilitation of Unilateral Spatial Neglect (USN). Two processes are involved in PA: i) recalibration (the reduction of the error of manual pointings toward the direction of the prism-induced displacement of the visual scene); ii) the successive realignment after prisms' removal, indexed by the Aftereffects (AEs, in egocentric straight-ahead pointing tasks, the deviation in a direction opposite to the visual displacement previously induced by prisms). This study investigated the role of the posterior parietal cortex (PPC) of the right hemisphere in PA and AEs, by means of low frequency repetitive Transcranial Magnetic Stimulation (rTMS). Proprioceptive and Visuo-proprioceptive egocentric straight-ahead pointing tasks were used to assess the presence and magnitude of AEs. The primary right visual cortex (V1) was also stimulated, to assess the selectivity of the PPC effects on the two processes of PA (recalibration and realignment) in comparison with a cortical region involved in visual processing. Results showed a slower adaptation to prisms when rTMS was delivered before PA, regardless of target site (right PPC or V1). AEs were reduced only by PPC rTMS applied before or after PA, as compared to a sham stimulation. These findings suggest a functional and neural dissociation between realignment and recalibration. Indeed, PA interference was induced by rTMS to both the PPC and V1, indicating that recalibration is supported by a parieto-occipital network. Conversely, AEs were disrupted only by rTMS delivered to the PPC, thus unveiling a relevant role of this region in the development and maintenance of the realignment.

A brief exposure to rightward prismatic adaptation changes resting-state network characteristics of the ventral attentional system

A brief session of rightward prismatic adaptation (R-PA) has been shown to alleviate neglect symptoms in patients with right hemispheric damage, very likely by switching hemispheric dominance of the ventral attentional network (VAN) from the right to the left and by changing task-related activity within the dorsal attentional network (DAN). We have investigated this very rapid change in functional organisation with a network approach by comparing resting-state connectivity before and after a brief exposure i) to R-PA (14 normal subjects; experimental condition) or ii) to plain glasses (12 normal subjects; control condition). A whole brain analysis (comprising 129 regions of interest) highlighted R-PA-induced changes within a bilateral, fronto-temporal network, which consisted of 13 nodes and 11 edges; all edges involved one of 4 frontal nodes, which were part of VAN. The analysis of network characteristics within VAN and DAN revealed a R-PA-induced decrease in connectivity strength between nodes and a decrease in local efficiency within VAN but not within DAN. These results indicate that the resting-state connectivity configuration of VAN is modulated by R-PA, possibly by decreasing its modularity.

Impaired Adaptive Motor Learning Is Correlated With Cerebellar Hemispheric Gray Matter Atrophy in Spinocerebellar Ataxia Patients: A Voxel-Based Morphometry Study

Objective: To evaluate the degree to which recently proposed parameters measured via a prism adaptation task are correlated with changes in cerebellar structure, specifically gray matter volume (GMV), in patients with spinocerebellar degeneration (SCD). Methods: We performed whole-brain voxel-based morphometry (VBM) analysis on 3-dimensional T1-weighted images obtained from 23 patients with SCD [Spinocerebellar ataxia type 6 (SCA6), 31 (SCA31), 3/Machado-Joseph disease (SCA3/MJD), and sporadic cortical cerebellar atrophy (CCA)] and 21 sex- and age-matched healthy controls (HC group). We quantified a composite index representing adaptive motor learning abilities in a hand-reaching task with prism adaptation. After controlling for age, sex, and total intracranial volume, we analyzed group-wise differences in GMV and regional GMV correlations with the adaptive learning index. Results: Compared with the HC group, the SCD group showed reduced adaptive learning abilities and smaller GMV widely in the lobules IV-VIII in the bilateral cerebellar hemispheres. In the SCD group, the adaptive learning index was correlated with cerebellar hemispheric atrophy in the right lobule VI, the left Crus I. Additionally, GMV of the left supramarginal gyrus showed a correlation with the adaptive learning index in the SCD group, while the supramarginal region did not accompany reduction of GMV. Conclusions: This study indicated that a composite index derived from a prism adaptation task was correlated with GMV of the lateral cerebellum and the supramarginal gyrus in patients with SCD. This study should contribute to the development of objective biomarkers for disease severity and progression in SCD.