Testing for spatial neglect with line bisection and target cancellation: are both tasks really unrelated?

Abstract

Damage to the parietal lobe can induce a condition known as spatial neglect, characterized by a lack of awareness of the personal and/or extrapersonal space opposite the damaged brain region. Spatial neglect is commonly assessed clinically using either the line bisection or the target cancellation task. However, it is unclear whether poor performance on each of these two tasks is associated with the same or different lesion locations. To date, methodological limitations and differences have prevented a definitive link between task performance and lesion location to be made. Here we report findings from a voxel-based lesion symptom mapping (VLSM) analysis of an unbiased selection of 44 patients with a recent unifocal stroke. Patients performed both the line bisection and target cancellation task. For each of the two tasks a continuous score was incorporated into the VLSM analysis. Both tasks correlated highly with each other (r = .76) and VLSM analyses indicated that the angular gyrus was the critical lesion site for both tasks. The results suggest that both tasks probe the same underlying cortical deficits and although the cancellation task was more sensitive than the line bisection task, both can be used in a clinical setting to test for spatial neglect.

Figure 1. Lesion distribution volume map for all subjects (n = 44).

The color code indicates in how many individuals a given voxel was lesioned (ranging from 1 to 13).

Figure 2. Lesion-symptom maps for all subjects (n = 44) showing results for the target cancellation task (neglect score 1, A), and the line bisection task (neglect score 2, B).

With both tasks, the posterior medial part of the angular gyrus (red areas) was associated with significant deficits. The input threshold for the cancellation task was set at FDR<0.01, and for the line bisection task it was set at FDR <0.05.