Eye position signals in the pathophysiology of spatial neglect
Research type
Research Study
Full title
The role of the cortical eye position signals in the pathophysiology of spatial neglect
IRAS ID
158579
Contact name
Daniela Balslev
Contact email
Duration of Study in the UK
3 years, 5 months, 31 days
Research summary
Patients with spatial neglect are not aware of stimuli located on the side opposite the brain lesion despite their adequate vision or hearing. This is a common and devastating condition in brain damaged patients. One in three and sometimes up to eight in ten stroke survivors suffer from spatial neglect, which renders them unable to carry out everyday tasks such as getting dressed, eating, reading or crossing the street on their own. So far there is no treatment for spatial neglect that works in the long term.
The mechanisms underlying the core spatial attention deficit remain unclear. There is an obvious link between eye position and spatial attention. The brain uses the position of the eyes to work out where to direct attention. This means that every time we move our eyes, our brain must update to take this change of position into account. To keep track of important objects across eye movements or to orient towards a sound, these eye-centred representations must be combined with information about the rotation of one's own eyes in the orbits. Strikingly, no research to date has exploited the link to understand spatial neglect. Here, I will ask whether spatial neglect is caused by a faulty eye position input to the brain areas that control the allocation of attention in space.
I will collect behavioral, eye tracking as well as structural and functional magnetic resonance imaging (MRI, fMRI) data in healthy participants and stroke patients. The experiments will take place at the Clinical Research Centre, Ninewells. Patient recruitment will take place in the Acute Stroke Unit, Ninewells in collaboration with the consultant physician Dr Chandrashekar and the ocupational therapist Ms Wheadon.
Summary of Results
Up to one-third of patients with an acute stroke are unaware of people and objects located to the left side of their body, as if they were blind to that part of the world. Spatial neglect is not a disorder of the eye, but rather a problem in allocating attention. Compared with other stroke patients, those who suffer from spatial neglect are less able to carry out everyday tasks like eating or getting dressed independently. They spend more days in the hospital and are also twice as likely to be discharged to an institution rather than to their own home. Subtle visual deficits persist in the long term and there is so far no evidence for a rehabilitation method that works for all patients.One reason current therapies don't work could be that the theories of what causes spatial neglect are not correct. We want to investigate a simple hypothesis that has so far been overlooked. Basic biological research has uncovered a link between sensing the direction in which one's own eyes point and the ability to attend to visual objects around the body. Patients with left spatial neglect perceive that they look further to the right than they actually do (Balslev & Odoj, 2019). Could an error in sensing the direction of one's own gaze lead to spatial neglect?
This project formed the first step in investigating this hypothesis.
The main findings are:• Optokinetic stimulation, one of the most promising therapies in spatial neglect, whose mechanisms of action remain unknown, alters the perceived direction of one’s own gaze in healthy volunteers (Chan et al., 2024)
• Brain areas that send movement commands to the muscles that move the eyes also receive sensory information from these muscles about the direction in which the eyes point (Balslev et al., 2022)
• When an attention-grabbing, unexpected stimulus appears in their neglected visual field, patients with spatial neglect involuntarily orient attention to a different, specific location in the “normal” visual field (Balslev, Mitchell, Lambert, Cvoro, in preparation).
This research was funded by a seedcorn award from the University of St Andrews. It has provided supporting evidence and pilot data for a research grant application to be submitted to the MRC Experimental Medicine Board in October 2024. The research we are now proposing aims to investigate whether an intervention that corrects the error in perceived gaze also alleviates spatial neglect.
REC name
North West - Greater Manchester South Research Ethics Committee
REC reference
14/NW/1525
Date of REC Opinion
12 May 2015
REC opinion
Further Information Favourable Opinion