Abstract
The arcuate fasciculus (AF) in the human brain has asymmetric structural properties. However, the topographic organization of the asymmetric AF projections to the cortex and its relevance to cortical function remain unclear. Here we mapped the posterior projections of the human AF in the inferior parietal and lateral temporal cortices using surface-based structural connectivity analysis based on diffusion MRI and investigated their hemispheric differences. We then performed the cross-modal comparison with functional connectivity based on resting-state functional MRI (fMRI) and task-related cortical activation based on fMRI using a semantic classification task of single words. Structural connectivity analysis showed that the left AF connecting to Broca's area predominantly projected in the lateral temporal cortex extending from the posterior superior temporal gyrus to the mid part of the superior temporal sulcus and the middle temporal gyrus, whereas the right AF connecting to the right homolog of Broca's area predominantly projected to the inferior parietal cortex extending from the mid part of the supramarginal gyrus to the anterior part of the angular gyrus. The left-lateralized projection regions of the AF in the left temporal cortex had asymmetric functional connectivity with Broca's area, indicating structure-function concordance through the AF. During the language task, left-lateralized cortical activation was observed. Among them, the brain responses in the temporal cortex and Broca's area that were connected through the left-lateralized AF pathway were specifically correlated across subjects. These results suggest that the human left AF, which structurally and functionally connects the mid temporal cortex and Broca's area in asymmetrical fashion, coordinates the cortical activity in these remote cortices during a semantic decision task. The unique feature of the left AF is discussed in the context of the human capacity for language.
Highlights
Asymmetric organization of structural and functional network is a fundamental characteristic of the brain, on which a variety of cognitive process depends (Geschwind and Galaburda, 1985; Toga and Thompson, 2003; Liu et al, 2009)
A statistical comparison between the two hemispheres (Figure 3B) showed that the right arcuate fasciculus (AF) predominantly projected to a cortical region extending from the mid part of the supramarginal gyrus to the anterior part of the angular gyrus, whereas the left AF predominantly projected to a cortical region extending from the posterior superior temporal gyrus (STG) to the mid superior temporal sulcus (STS)/middle temporal gyrus (MTG)
Asymmetric Organization of the Human Arcuate Fasciculus Projections In the current study, we demonstrated the asymmetric distribution of the human AF projections in the inferior parietal and lateral temporal cortices using surface-based structural connectivity analysis based on diffusion MRI tractography
Summary
Asymmetric organization of structural and functional network is a fundamental characteristic of the brain, on which a variety of cognitive process depends (Geschwind and Galaburda, 1985; Toga and Thompson, 2003; Liu et al, 2009). Investigating asymmetry in structural network and its functional relevance may provide insights into better understanding of human brain evolution and development. Previous studies have demonstrated a general correspondence between structural and functional network in the human brain (Koch et al, 2002; Hagmann et al, 2008; Skudlarski et al, 2008; Honey et al, 2009). The structure-function relationship of a specific fiber pathway in the context of the specialized cortical function in the human brain remains poorly understood. Given functional operation in the brain is done with the interaction between the remote cortices through the white matter pathway, an asymmetric white matter pathway is likely to be related to the functional lateralization of the cortex
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