Left-handedness and language lateralization in children

Abstract

This fMRI study investigated the development of language lateralization in left- and righthanded children between 5 and 18 years of age. Twenty-seven left-handed children (17 boys, 10 girls) and 54 age- and gender-matched right-handed children were included. We used functional MRI at 3T and a verb generation task to measure hemispheric language dominance based on either frontal or temporo-parietal regions of interest (ROIs) defined for the entire group and applied on an individual basis. Based on the frontal ROI, in the left-handed group, 23 participants (85%) demonstrated left-hemispheric language lateralization, 3 (11%) demonstrated symmetric activation, and 1 (4%) demonstrated right-hemispheric lateralization. In contrast, 50 (93%) of the right-handed children showed left-hemispheric lateralization and 3 (6%) demonstrated a symmetric activation pattern, while one (2%) demonstrated a right-hemispheric lateralization. The corresponding values for the temporo-parietal ROI for the left-handed children were 18 (67%) left-dominant, 6 (22%) symmetric, 3 (11%) right-dominant and for the right-handed children 49 (91%), 4 (7%), 1 (2%), respectively. Left-hemispheric language lateralization increased with age in both groups but somewhat different lateralization trajectories were observed in girls when compared to boys. The incidence of atypical language lateralization in left-handed children in this study was similar to that reported in adults. We also found similar rates of increase in left-hemispheric language lateralization with age between groups (i.e., independent of handedness) indicating the presence of similar mechanisms for language lateralization in left- and right-handed children.

Figure 1

Composite activation map for the verb generation task based on random effects analysis for all left-handed (A; N = 27) and right-handed (B; N = 54) subjects. Images are in radiologic convention with left in the brain corresponding to the right in the figure. These activation maps were generated using cluster size = 30; smoothing filter = 2 mm, corrected p-value <0.05. Higher intensity of activations in the right-handed children when compared to left-handed children are related to higher number of subjects included in the right-handed group.

Figure 2

Top: Distribution of LIs in the frontal and temporal-parietal ROI’s for right- and left-handed children. Bottom: Lateralization growth curves for the left- and right-handed children for the two ROI’s. Linear regression fits are shown along with individual lateralization index values of each subject by age.

Figure 3

Composite grey-scale T1 image showing regions of interest (ROI) used for computation of lateralization index (LI) for all subjects based on the results of ICA of all included subjects (N = 81). This region of interest is similar to the ICA “component D” described in our previous publication (Karunanayaka, Schmithorst et al. 2010). Spatial coordinates of the left frontal centroid are −36, 13, 24 and of the left temporal centroid −38, −50, 23; images are in radiologic convention with left in the brain corresponding to the right in the figure. Frontal lobe ROIs are shown anterior to the dashed white line and the temporo-parietal ROIs are shown posterior to the dashed line.