Microstructural development: organizational differences of the fiber architecture between children and adults in dorsal and ventral visual streams

Abstract

Visual perceptual skills are basically mature by the age of 7 years. White matter, however, continues to develop until late adolescence. Here, we examined children (aged 5-7 years) and adults (aged 20-30 years) using diffusion tensor imaging (DTI) fiber tracking to investigate the microstructural maturation of the visual system. We characterized the brain volumes, DTI indices, and architecture of visual fiber tracts passing through white matter structures adjacent to occipital and parietal cortex (dorsal stream), and to occipital and temporal cortex (ventral stream). Dorsal, but not ventral visual stream pathways were found to increase in volume during maturation. DTI indices revealed expected maturational differences, manifested as decreased mean and radial diffusivities and increased fractional anisotropy in both streams. Additionally, fractional anisotropy was increased and radial diffusivity was decreased in the adult dorsal stream, which can be explained by specific dorsal stream myelination or increasing fiber compaction. Adult dorsal stream architecture showed additional intra- and interhemispheric connections: Dorsal fibers penetrated into contralateral hemispheres via commissural structures and projection fibers extended to the superior temporal gyrus and ventral association pathways. Moreover, intra-hemispheric connectivity was particularly strong in adult dorsal stream of the right hemisphere. Ventral stream architecture also differed between adults and children. Adults revealed additional connections to posterior lateral areas (occipital-temporal gyrus), whereas children showed connections to posterior medial areas (posterior parahippocampal and lingual gyrus). Hence, in addition to dorsal stream myelination or fiber compaction, progressing maturation of intra- and interhemispheric connectivity may contribute to the development of the visual system.

Figure 1

Bar graphs of (A) mean FA, (B) mean MD, (C) mean AD, and (D) mean RD for the left dorsal, right dorsal, left ventral, and right ventral visual streams of children (dark gray) and adults (light gray). Presented values represent mean group indices derived from the union of the adult and children group visit‐masks after applying a threshold of 60% within‐group concordance. Error bars symbolize standard deviations.

Figure 2

Dorsal (A) and ventral streams (B) (neurological convention, axial view) representing voxels with 60% or more within group concordance. Common fiber tracts of both groups are marked in yellow; fibers exclusively found in adults are red and those exclusively found in children blue. Labels refer to areas of major differences in the fiber architecture of adults (red) and children (blue) as described in the text. Dorsal streams are separately displayed for left (top) and right (bottom) streams. As left and right ventral stream structures do not overlap they are combined in one figure. 2A‐top: (1) left middle temporal gyrus (MTG), (2) left cuneus, (3) bilateral posterior cingulate gyrus (PCG), (4) bilateral inferior parietal lobule (IPL), (5) right MTG, (6) bilateral BA18, (7) right BA19, (8) left middle occipital gyrus (MOG), (9) left BA7, cuneus, and precuneus; 2A‐bottom: (1) right BA17, (2) left BA30, (3) right STG, (4) right BA19. 2B: (1) right BA36, (2) right BA37, (3) right lingual gyrus, (4) right BA21, (5) left IOG, (6) left BA36, (7) left BA18, (8) left BA20, (9) left BA36. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]