Structural connectivity asymmetry in the neonatal brain

Abstract

Asymmetry of the neonatal brain is not yet understood at the level of structural connectivity. We utilized DTI deterministic tractography and structural network analysis based on graph theory to determine the pattern of structural connectivity asymmetry in 124 normal neonates. We tracted white matter axonal pathways characterizing interregional connections among brain regions and inferred asymmetry in left and right anatomical network properties. Our findings revealed that in neonates, small-world characteristics were exhibited, but did not differ between the two hemispheres, suggesting that neighboring brain regions connect tightly with each other, and that one region is only a few paths away from any other region within each hemisphere. Moreover, the neonatal brain showed greater structural efficiency in the left hemisphere than that in the right. In neonates, brain regions involved in motor, language, and memory functions play crucial roles in efficient communication in the left hemisphere, while brain regions involved in emotional processes play crucial roles in efficient communication in the right hemisphere. These findings suggest that even at birth, the topology of each cerebral hemisphere is organized in an efficient and compact manner that maps onto asymmetric functional specializations seen in adults, implying lateralized brain functions in infancy.

Figure 1

A schematic diagram illustrates the major processes involved in generating the neonatal brain networks. A. DW images of each subject are aligned to those of the neonatal atlas; B. the parcellation of cortical and subcortical regions using the neonatal brain atlas; C. the whole brain tractography using DTI deterministic tractography; D. the nodes (red balls) represent cortical and subcortical regions; E. weighted edges (green lines) obtained using the tract information.

Figure 2

Lateralization indices of global efficiency (A) and local efficiency (B) for all the 124 subjects.

Figure 3

The mean lateralization index of betweenness centrality for the 32 defined cortical and subcortical regions. The abbreviations of the structures are given in Table 1.

Figure 4

Neural substrates with structural asymmetry in the betweenness centrality. The neural substrates with leftward asymmetry are colored in green, while the neural substrates with right asymmetry are colored in blue. The abbreviations of these substrates are given in Table 1.