The ipsilesional attention bias in right-hemisphere stroke patients as revealed by a realistic visual search task: Neuroanatomical correlates and functional relevance.

Abstract

Objective Right hemisphere stroke may cause an ipsilesional attention bias and left hemispatial neglect. Computerized time-limited tasks are more sensitive than conventional paper-pencil tests in detecting these spatial attention deficits. However, their frequency in the acute stage of stroke, the neuroanatomical basis and functional relevance for patients’ everyday life are unclear. Method A realistic visual search task is introduced, in which eye movements are recorded while the patient searches for paperclips among different everyday objects on a computer display. The “Desk task” performance of 34 acute right hemisphere stroke patients was compared to established paper-pencil tests for neglect and the Posner reaction time task, and finally correlated to structural brain lesions. Results Most of the patients, even those without clinical neglect signs and with normal paper-pencil test performance, exhibited a clear ipsilesional attention bias in the Desk task. This bias was highly correlated to the left-right asymmetry in the Posner task and to neglect-related functional impairment scores. Lesion-symptom mapping revealed task-specific differences: deficits in the Desk task were associated with lesions of the superior temporal gyrus, contralesional unawareness in the Posner task with ventral frontal cortex lesions and paper-pencil cancellation bias with damage to the inferior parietal lobe. Neglect behavior was further associated with distinct fronto-parietal white matter tract disconnections (ILF, SLF, Arcuate). Conclusions Results from the novel Desk task indicate a functional relevance of spatial attention deficits in right brain damaged patients, even if they are “subclinical”. This should be considered especially in patients without obvious clinical neglect signs.

Unbalancing the Attentional Priority Map via Gaze-Contingent Displays Induces Neglect-Like Visual Exploration

“…We detected a rightward bias of exploratory fixations in the outer parts of the visual scene, most pronounced for the strongest type of modification (LHypo+RHyper) in the free viewing condition. Such a spatial asymmetry with avoidance of the far left and ''hyper-exploration'' of the far right is also found in patients with left hemispatial neglect (Behrmann et al, 1997;Sprenger et al, 2002;Müri et al, 2009;Delazer et al, 2018;Machner et al, 2018).…”

“…Our modification could also not induce an enduring shift of exploratory eye movements towards the right hemifield as it is typically seen in patients with hemispatial neglect who exhibit an ipsilesional shift of the ''center of fixation'' of about 5-15 • (Karnath and Fetter, 1995;Machner et al, 2012Machner et al, , 2018. There are different possible explanations: first, our saliency modification might not have been strong enough to elicit such a pronounced shift of the center of fixation.…”

“…Although neglect is known to represent a multi-component syndrome, that also includes non-lateralized deficits such as an impairment in spatial working memory and sustained attention (Husain and Rorden, 2003), the egocentric bias away from contralesional and towards ipsilesional hemispace is regarded as the core symptom of spatial neglect (Parton et al, 2004;Corbetta and Shulman, 2011). This bias can be elegantly studied by using eye movement recordings during computerized tasks of spatial attention (Chédru et al, 1973;Behrmann et al, 1997;Sprenger et al, 2002;Mort and Kennard, 2003;Bonato, 2012;Machner et al, 2012Machner et al, , 2018.…”

Ipsilesional Impairments of Visual Awareness After Right-Hemispheric Stroke

“…Nevertheless, the observation of errorless performance for the most lateralized ipsilesional locations might depend on ceiling effects. Recently Machner et al (2018) showed that the most severe neglect patients they tested were slower than controls in detecting ipsilesional targets in a Posner detection task, while in a search task they processed the most ipsilesional targets with the same accuracy as healthy controls (i.e., almost errorless).…”

Brain Activations During Optokinetic Stimulation in Acute Right-Hemisphere Stroke Patients and Hemispatial Neglect: An fMRI Study

“…This task has been proven very sensitive in detecting even mild subclinical signs of lateralized inattention, otherwise missed by established paper-and-pencil tests and clinical observation. 34 Eye movements were recorded in order to obtain information on an ipsilesional oculomotor/attention bias during overt shifts of spatial attention (as opposed to the rather reflexive pattern of an optokinetic nystagmus in the OKS task). Based on the horizontal fixation distribution of eye movements on the screen, we calculated the center of fixation ( CoF ), which corresponds to the median x-position on the screen from where 50% of all fixations were located on the left and 50% on the right.…”