Developmental Changes in Neural Lateralization for Visual-Spatial Function? Evidence From a Line-Bisection Task

Abstract

Studies of hemispheric specialization have traditionally cast the left hemisphere as specialized for language and the right hemisphere for spatial function. Much of the supporting evidence for this separation of function comes from studies of healthy adults and those who have sustained lesions to the right or left hemisphere. However, we know little about the developmental origins of lateralization. Recent evidence suggests that the young brain represents language bilaterally, with 4-6-year-olds activating the left-hemisphere regions known to support language in adults as well as homotopic regions in the right hemisphere. This bilateral pattern changes over development, converging on left-hemispheric activation in late childhood. In the present study, we ask whether this same developmental trajectory is observed in a spatial task, that is, strongly right-lateralized in adults-the line bisection (or "Landmark") task. We examined fMRI activation among children ages 5-12 years as they were asked to judge which end of a bisected vertical line was longer. We found that young children showed right-lateralized activation in the same parietal and posterior temporal areas as has been shown among adults, with no significant effects of age on lateralization within the age range we tested. We discuss potential underlying mechanisms and suggest that understanding the development of lateralization for a range of cognitive functions can play a crucial role in understanding general principles of how and why the brain comes to lateralize certain functions. SUMMARY: -Functional MRI was used to examine neural activation associated with a line bisection task in children ages 5-12 years. -Children showed right-lateralized activation in the same areas previously identified among adults. -There were no effects of children's age on the degree of right-lateralization. -This illustrates stable lateralization over development for the line bisection task and contrasts with findings of increasing lateralization over age in the domain of language.

FIGURE 1

Experimental design. (a) Spatial condition: participants indicated whether the bottom or top part of the line was longer. (b) Luminance condition: participants indicated whether the bottom or top part of the line was brighter.

FIGURE 2

Behavioral performance on the “Line Game.” (a) Average proportion of correct responses for the Spatial and Luminance conditions. (b) Average reaction time (RT) for the Spatial and Luminance conditions. Error bars represent ± standard error of the mean.

FIGURE 3

Group‐level activation map across all child participants: Areas displaying significantly stronger activation for the contrast of Spatial > Luminance for the line bisection task. Activation was observed in the right hemisphere in the fusiform gyrus (FG, BA 37) and in the inferior parietal lobule (IPL, BA 40) in two clusters. Activation maps are overlaid on the Colin27 brain template transformed into Talairach space and thresholded at p < 0.001 single‐voxel threshold combined with a k < 0.05 cluster‐size threshold. Activation details can be found in Table 1.

FIGURE 4

Individual participant activation patterns (contrast: Spatial > Luminance). Activation maps are overlaid on the individual's MPRAGE, transformed into Talairach space, and thresholded at p < 0.001 single‐voxel threshold combined with a k < 0.05 cluster‐size threshold. See Figure S4 for additional examples of individual activation maps.

FIGURE 5

Lateralization analysis. (a) The anatomically‐defined bilateral posterior parietal ROI encompassing Brodmann areas 7, 40, and 39 was used to analyze lateralization of function in children for the line bisection task. (b) Lateralization index values for individual child participants for the contrast Spatial > Luminance. The linear trendline of the data is shown. For illustration purposes, the adult mean LI for this same task (Seydell‐Greenwald et al. 2019) is shown in red. This illustrates that the LIs of children between ages 5 and 12 tend to be right‐lateralized and are distributed around the adult mean, with no apparent lateralization increase over age.