Line bisection and cognitive plasticity of unilateral neglect of space

doi:10.1016/0278-2626(83)90027-1

Brain and Cognition

Volume 2, Issue 1, January 1983, Pages 32-38

https://doi.org/10.1016/0278-2626(83)90027-1 Get rights and content

Abstract

Patients with neglect of the left half of space were asked to bisect lines of different lengths. The leftmost points of the represented lines, determined on the basis of the midpoints set by the patients on the objective lines, were the dependent variable. It was thus possible to recognize diverse patterns of behavior which were conceivably averaged away in earlier investigations. In discussing the results, the question is raised of whether unilateral neglect of space may be altered by cognitive processes.

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Investigating visuo-spatial neglect and visual extinction during intracranial electrical stimulations: The role of the right inferior parietal cortex
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Both visuo-spatial neglect and visual extinction may occur following right-brain damage. So far, studies on brain-damaged patients have not provided definite evidence about which lesion patterns may lead to the association or dissociation of these deficits. This study was set out to address this issue using Intracranial Electrical Stimulation (IES) in a group of nine patients affected by refractory epilepsy. Cerebral regions associated with visuo-spatial neglect and visual extinction were stimulated, including the right frontal, temporal, and posterior parietal areas. During IES, patients with intracranial implantation involving at least one of these cortical regions were administered with a manual line bisection task (N = 9) to assess visuo-spatial neglect, and a computerized task (N = 8) assessing visual extinction. Results showed that parietal IES induced a rightward bias at the manual bisection task, together with a general improvement in reaction times at bilateral and unilateral visual stimuli detection at the extinction task. The occurrence of visual extinction did not vary across stimulations. By adopting a complementary approach to anatomo-clinical correlation studies, our work corroborates the notion that lesions to the right inferior parietal lobule play a pivotal role in the pathogenesis of visuo-spatial neglect. Importantly, our results also suggest that temporarily interfering with the activity of this region is not sufficient per se to generate visual extinction, which instead may involve a broader and/or different network, possibly extending beyond the cerebral regions considered here, posing important theoretical and clinical implications.
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The human brain has a remarkable capacity to focus processing resources based on the features and the relevance of the task at hand. The two cerebral hemispheres contribute differentially to this capacity, with the left hemisphere linguistic and right hemisphere visuo-spatial abilities each offering unique contributions. For example, previous research has established that healthy participants set the subjective mid-point of written sentences more leftwards of center, compared to unpronounceable letter strings or simple lines. Remarkably, patients with right hemisphere damage exhibiting unilateral spatial neglect also show this pattern, even though, as well known in the literature, they tend toward a rightward- bias for non-linguistic stimuli. This evidence suggests that the leftward bias for sentential material is due to linguistic, mainly left-hemisphere mediated processes, which are largely unimpaired in right brain-damaged patients, and intact in heathy participants. To test this hypothesis, we compared sentence bisection performance to that of letter strings and simple lines in left brain-damaged patients (with and without aphasia). If the larger leftward bias in the bisection of sentential material is based on linguistic processes, then the left brain-damaged patients should show a reduction or absence of a leftward bias in sentence bisection. We tested twenty-four left brain-damaged patients (12 with aphasia and 12 without aphasia), and 24 age-matched elderly participants (patients and controls were all right-handed). Participants were asked to bisect 240 stimuli, comprising: (i) affirmative and interrogative clauses, (ii) sentences with lexical and syntactic violations, (iii) letter strings and (iv) simple lines. As predicted, neurologically intact participants showed larger leftward biases in bisecting written readable sentences compared to strings of letters. In contrast, the left hemispheredamaged patients (both with and without aphasia) showed no differences in bisecting sentences and letter strings or lines. These findings indicate that the larger leftward bias exhibited by healthy participants in the bisection of sentences is likely due to ortho-phonological coding taking place implicitly during the bisection task. This ortho-phonological coding is impaired with left brain damage – also in absence of apparent aphasia – leading to the left hemispheredamaged patients showing a reduced leftward bias in sentence bisection. These findings support the hypothesis that the leftward bias in the bisection of written sentences is the result of ortho-phonological influences rather than visual-spatial biases.
The Neural Mechanism of Number Line Bisection: A fMRI study
2019, Neuropsychologia
Citation Excerpt :
The physical line bisection task is often used to diagnose unilateral visuospatial neglect (e.g., Marshall and Halligan, 1989; Marshall et al., 1997). Because of right brain damage, these patients show unilateral neglect of visual information on the left side; in particular, when asked to mark the midpoint of a physical line, they usually place it to the right (Bisiach et al., 1983). In a seminal study, Zorzi et al. (2002) found that right brain-damaged patients show deviations in the number line bisection task, similar to what is typically observed in physical line bisection.
The neural networks involved in number line bisection are poorly understood. We used functional magnetic resonance imaging (fMRI) to investigate these. fMRI was analyzed from 28 healthy volunteers who performed number and physical line bisection tasks (and their respective baselines). Whole brain analyses showed that these two bisection tasks shared common neural correlates in bilateral parietal-frontal networks; furthermore, bilateral parietal-frontal areas, right cerebellum, left insula and supplementary motor area (SMA) showed higher activity when contrasting the number line with a physical line bisection task. Importantly, psychophysiological interaction (PPI) analyses further indicated that left SMA and right cerebellum were connected to parietal-frontal areas for implementing the number line bisection task. Our findings suggested that a visuospatial attention control system was recruited, and mental imagery of a number line was used to find the midpoint of a numerical interval without calculations.

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^☆: Research was supported by CNR Grant CT8001829.

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Line bisection and cognitive plasticity of unilateral neglect of space☆

Abstract

Neuropsychologia

Neuropsychologia

Phenomena of fluctuation, extinction and completion in visual perception

Archives of Neurology and Psychiatry

Halving a horizontal segment: A study on hemisphere damaged patients with cerebral focal lesions

Archives Suisses de Neurologie, Neurochirurgie et de Psychiatrie

Unilateral neglect, representational schema and consciousness

Brain