Structural and functional reorganization of the corpus callosum between the age of 6 and 8 years

Abstract

The establishment of an efficient exchange of information between the cerebral hemispheres is of crucial importance in the developing functionally lateralized brain. The corpus callosum, the major connection between the cerebral hemispheres, grows constantly throughout childhood and adolescence. However, behavioral studies suggest the existence of a critical time period for callosal functional development starting around the age of 6 years. In the present longitudinal study, examining a cohort of 20 children at the age of 6 and 8 years, we assessed the relationship between structural and functional callosal development during this time period. The structural development was quantified by calculating the increase in callosal thickness using a shape-based computational analysis of the mid-sagittal corpus callosum as obtained with magnetic resonance imaging. The functional development was assessed with a speech discrimination task based on the dichotic presentation of consonant-vowel syllables. The statistical analysis revealed that children whose callosal isthmus increased in thickness over the course of 2 years showed a decrease in interhemispheric information transfer. However, children exhibiting a decrease in isthmus thickness revealed an increase in information transfer. These results might indicate a refinement process of the callosal connections to optimize the neuronal communication between the developing cerebral hemispheres.

Figure 1.

Differences in callosal thickness between 6- and 8-year-old children. Panel A displays callosal regions that showed a significantly larger thickness at age 6; Panel B displays callosal regions that showed a significantly larger thickness at age 8. The color bar encodes the significance (P). The circle indicates the location of the callosal isthmus.

Figure 2.

Correlations between changes in LE report (ΔLE) and changes in callosal regional thickness between the age of 6 and 8 years. Panel A displays the callosal regions that showed significant negative correlations at P < 0.05. The color bar encodes the correlation coefficient (r). Panel B displays the scatter plot for the highest magnitude correlation, which was located in the isthmus. The circle indicates the location of the callosal isthmus.

Figure 3.

Correlations between LE report and RE report and callosal thickness in different age groups. Displayed are the locations of significant negative (red) and positive (blue) correlations between callosal size and LE (upper row) and RE (lower row). The maps are displayed for children at the age of 6 years (left) and 8 years (middle), as well as for an adult control group (right). The maximum correlations (r) are provided for each of the regions in which a significant correlation (P < 0.05) was detected. The circle indicates the callosal isthmus.