Strengthening of laterality of verbal and visuospatial functions during childhood and adolescence

Abstract

Cognitive functions in the child's brain develop in the context of complex adaptive processes, determined by genetic and environmental factors. Little is known about the cerebral representation of cognitive functions during development. In particular, knowledge about the development of right hemispheric (RH) functions is scarce. Considering the dynamics of brain development, localization and lateralization of cognitive functions must be expected to change with age. Twenty healthy subjects (8.6-20.5 years) were examined with fMRI and neuropsychological tests. All participants completed two fMRI tasks known to activate left hemispheric (LH) regions (language tasks) and two tasks known to involve predominantly RH areas (visual search tasks). A laterality index (LI) was computed to determine the asymmetry of activation. Group analysis revealed unilateral activation of the LH language circuitry during language tasks while visual search tasks induced a more widespread RH activation pattern in frontal, superior temporal, and occipital areas. Laterality of language increased between the ages of 8-20 in frontal (r = 0.392, P = 0.049) and temporal (r = 0.387, P = 0.051) areas. The asymmetry of visual search functions increased in frontal (r = -0.525, P = 0.009) and parietal (r = -0.439, P = 0.027) regions. A positive correlation was found between Verbal-IQ and the LI during a language task (r = 0.585, P = 0.028), while visuospatial skills correlated with LIs of visual search (r = -0.621, P = 0.018). To summarize, cognitive development is accompanied by changes in the functional representation of neuronal circuitries, with a strengthening of lateralization not only for LH but also for RH functions. Our data show that age and performance, independently, account for the increases of laterality with age.

Figure 1

Activation (left) and contrast (right) condition of the two language tasks (above) and the visual search tasks (below). Original tasks were presented in color.

Figure 2

Group analysis of children (n = 20) during the two visual search tasks (left) and the two language tasks (right). Group analysis: n = 20, random effect analysis, P < 0.05, FWE‐corrected, extended threshold k > 50 voxels. One child (animal search task) or two children (Rey search task) were excluded from analysis due to movement >3mm. See text for details regarding the identified activation sites. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Figure 3

Mean laterality indices (LI) over all brain regions of the four paradigms. Left lateralization was assumed at laterality index >0.2, right lateralization was assumed at laterality index <−0.2.

Figure 4

Relation between age at examination and laterality indices for the frontal and parietal region during the Rey search task (n = 19). * indicates significant correlation at the P < 0.05 level (partial 2‐tailed Pearson correlation controlling for visuo‐spatial performance, copy of the Rey Figure). One child with RH language is not included in the analysis.

Figure 5

Relation between age at examination and laterality indices for the frontal and temporal region in the vowel detection task (n = 19). * indicates significant correlation at the P < 0.05 level (partial 2‐tailed Pearson correlation controlling for Verbal‐IQ). One child with RH language is not included in the analysis.

Figure 6

Regression analyses according to age at examination. Regression: simple, P > 0.001, uncorrected. The regression analysis shows areas that are more active in older children compared to younger ones. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]