Lateralization of the arcuate fasciculus from childhood to adulthood and its relation to cognitive abilities in children

Abstract

The arcuate fasciculus is a major white matter tract involved in language processing that has also been repeatedly implicated in intelligence and reasoning tasks. Language in the human brain is lateralized in terms of both function and structure, and while the arcuate fasciculus reflects this asymmetry, its pattern of lateralization is poorly understood in children and adolescents. We used diffusion tensor imaging (DTI) and tractography to examine arcuate fasciculus lateralization in a large (n = 183) group of healthy right-handed volunteers aged 5-30 years; a subset of 68 children aged 5-13 years also underwent cognitive assessments. Fractional anisotropy and number of streamlines of the arcuate fasciculus were both significantly higher in the left hemisphere than the right hemisphere in most subjects, although some subjects (10%) were right lateralized. Age and gender effects on lateralization were not significant. Children receiving cognitive assessments were divided into three groups: a "left-only" group in whom only the left side of the arcuate fasciculus could be tracked, a left-lateralized group, and a right-lateralized group. Scores on the Peabody Picture Vocabulary Test (PPVT) and NEPSY Phonological Processing task differed significantly among groups, with left-only subjects outperforming the right-lateralized group on the PPVT, and the left-lateralized children scoring significantly better than the right-lateralized group on phonological processing. In summary, DTI tractography demonstrates leftward arcuate fasciculus lateralization in children, adolescents, and young adults, and reveals a relationship between structural white matter lateralization and specific cognitive abilities in children.

Figure 1

Schematic of tracking methods used to delineate the arcuate fasciculus. A manual two region‐of‐interest approach was used in which a seeding region was drawn on a coronal slice and a target region outlined on an axial slice in each hemisphere for each subject. Exclusion regions were used as needed to eliminate spurious streamlines, and were often needed in the area of the internal capsule. Tracts passing through both the seeding and target regions, without passing through exclusion regions, were retained for calculation of the lateralization index (LI). LI was calculated for each subject based on the number of streamlines in each hemisphere. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Figure 2

Lateralization index based on number of streamlines (LI) versus age graph for 183 right‐handed subjects, as well as sample arrangements of the arcuate fasciculus with various values of LI. Most individuals are left lateralized (LI > 0), although there are some right‐lateralized (LI < 0) subjects. LI was not significantly correlated with age nor was it significantly different between males and females. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Figure 3

Mean scores (±95% confidence intervals) for each test for different lateralization groups of 68 children aged 5–13 years. The Peabody Picture Vocabulary Test (PPVT) and NEPSY Phonological Processing scores differed significantly among groups, with the left‐only group scoring significantly better than the right‐lateralized group for the PPVT, and the left‐lateralized group significantly outperforming the right‐lateralized group for phonological processing.

Figure 4

Plots of lateralization index (LI) versus age‐standardized scores for (A) Peabody Picture Vocabulary Test (PPVT) and (B) NEPSY Phonological Processing for the entire group of 68 children with cognitive assessments. There was a significant linear correlation between PPVT and LI, whereas the linear correlation between Phonological Processing and LI was not significant. Note the significant lateralization group findings shown in Figure 3.