Midline Body Actions and Leftward Spatial "Aiming" in Patients with Spatial Neglect

Ego- and Geo-Centered References: A Functional Neuroimagery Study

INTRODUCTION

The integration of vestibular, visual, and somatosensory cues allows the perception of space through the orientation of our body and surrounding objects with respect to gravity. The main goal of this study was to identify the cortical networks recruited during the representation of body midline and the representation of verticality.

METHODS

Thirty right-handed healthy participants were evaluated using fMRI. Brain networks activated during a subjective straight-ahead (SSA) task were compared to those recruited during a subjective vertical (SV) task.

RESULTS

Different patterns of cortical activation were observed, with differential increases in the angular gyrus and left cerebellum posterior lobe during the SSA task, in right rolandic operculum and cerebellum anterior lobe during the SV task.

DISCUSSION

The activation of these areas involved in visuo-spatial functions suggests that bodily processes of great complexity are engaged in body representation and vertical perception. Interestingly, the common brain networks involved in SSA and SV tasks were comprised of areas of vestibular projection that receive multisensory information (parieto-occipital areas) and the cerebellum, and reveal a predominance of the right cerebral and cerebellar hemispheres. The outcomes of this first fMRI study designed to unmask common and specific neural mechanisms at work in gravity- or body-referenced tasks pave a new way for the exploration of spatial cognitive impairment in patients with vestibular or cortical disorders.

Recent advances in treatment of spatial neglect: networks and neuropsychology

INTRODUCTION

Spatial neglect remains an underdiagnosed and undertreated consequence of stroke that imposes significant disability. A growing appreciation of brain networks involved in spatial cognition is helping us to develop a mechanistic understanding of different therapies under development.

AREAS COVERED

This review focuses on neuromodulation of brain networks for the treatment of spatial neglect after stroke, using evidence-based approaches including 1) Cognitive strategies that are more likely to impact frontal lobe executive function networks; 2) Visuomotor adaptation, which may depend on the integrity of parietal and parieto- and subcortical-frontal connections and the presence of a particular subtype of neglect labeled Aiming neglect; 3) Non-invasive brain stimulation that may modulate relative levels of activity of the two hemispheres and depend on corpus callosum connectivity; and 4) Pharmacological modulation that may exert its effect primarily via right-lateralized networks more closely involved in arousal.

EXPERT OPINION

Despite promising results from individual studies, significant methodological heterogeneity between trials weakened conclusions drawn from meta-analyses. Improved classification of spatial neglect subtypes will benefit research and clinical care. Understanding the brain network mechanisms of different treatments and different types of spatial neglect will make possible a precision medicine treatment approach.

Spatial neglect treatment: The brain's spatial-motor Aiming systems

Animal and human literature supports spatial-motor "Aiming" bias, a frontal-subcortical syndrome, as a core deficit in spatial neglect. However, spatial neglect treatment studies rarely assess Aiming errors. Two knowledge gaps result: spatial neglect rehabilitation studies fail to capture the impact on motor-exploratory aspects of functional disability. Also, across spatial neglect treatment studies, discrepant treatment effects may also result from sampling different proportions of patients with Aiming bias. We review behavioural evidence for Aiming spatial neglect, and demonstrate the importance of measuring and targeting Aiming bias for treatment, by reviewing literature on Aiming spatial neglect and prism adaptation treatment, and presenting new preliminary data on bromocriptine treatment. Finally, we review neuroanatomical and network disruption that may give rise to Aiming spatial neglect. Because Aiming spatial neglect predicts prism adaptation treatment response, assessment may broaden the ability of rehabilitation research to capture functionally-relevant disability. Frontal brain lesions predict both the presence of Aiming spatial neglect, and a robust response to some spatial neglect interventions. Research is needed that co-stratifies spatial neglect patients by lesion location and Aiming spatial neglect, to personalize spatial neglect rehabilitation and perhaps even open a path to spatial retraining as a means of promoting better mobility after stroke.

Impact of eliminating visual input on sitting posture and head position in a patient with spatial neglect following cerebral hemorrhage: a case report

Background: Spatial neglect is a neurocognitive syndrome. Affected individuals pay little or insufficient attention to the space contralateral to the injured cerebral hemisphere, often resulting in or exacerbating disability following an acquired brain injury. Eliminating visual input may increase attention toward the contralesional side of space, and improve symptoms of spatial neglect; however this has never been examined in a clinical setting. Objective: In this case report, we observed an individual demonstrate immediate and spontaneous postural changes once visual input was eliminated. Methods: The patient, a 53-year-old female, was admitted to a rehabilitation hospital after hemorrhagic stroke affecting her right basal ganglia and surrounding regions in the frontal lobe. She exhibited left-sided spasticity, severe right gaze preference, and stark rightward postural deviation. Neck passive range of motion was normal. Visual field integrity was inconclusive due to poor communication and impaired cognitive function. Contraversive pushing was ruled out. Results:Once visual input was eliminated by applying a blindfold, the patient turned to the left spontaneously, had more buttock contact on the left, and placed more weight toward the left side in a sitting posture. However, she returned to rightward deviation three minutes after blindfold removal. In addition, the patient's rehabilitation team reported that she was able to participate in more therapy activities with binocular occlusion than with eyes open. Conclusion: Binocular occlusion appeared to demonstrate an immediate, albeit transient, improvement in postural symmetry. The results warrant further research and exploration in clinical applicability.