Abstract
The definitive structure and functional role of the inferior fronto-occipital fasciculus (IFOF) are still controversial. In this study, we aimed to investigate the connectivity, asymmetry, and segmentation patterns of this bundle. High angular diffusion spectrum imaging (DSI) analysis was performed on 10 healthy adults and a 90-subject DSI template (NTU-90 Atlas). In addition, a new tractography approach based on the anatomic subregions and two regions of interest (ROI) was evaluated for the fiber reconstructions. More widespread anterior-posterior connections than previous “standard” definition of the IFOF were found. This distinct pathway demonstrated a greater inter-subjects connective variability with a maximum of 40% overlap in its central part. The statistical results revealed no asymmetry between the left and right hemispheres and no significant differences existed in distributions of the IFOF according to sex. In addition, five subcomponents within the IFOF were identified according to the frontal areas of originations. As the subcomponents passed through the anterior floor of the external capsule, the fibers radiated to the posterior terminations. The most common connection patterns of the subcomponents were as follows: IFOF-I, from frontal polar cortex to occipital pole, inferior occipital lobe, middle occipital lobe, superior occipital lobe, and pericalcarine; IFOF-II, from orbito-frontal cortex to occipital pole, inferior occipital lobe, middle occipital lobe, superior occipital lobe, and pericalcarine; IFOF-III, from inferior frontal gyrus to inferior occipital lobe, middle occipital lobe, superior occipital lobe, occipital pole, and pericalcarine; IFOF-IV, from middle frontal gyrus to occipital pole, and inferior occipital lobe; IFOF-V, from superior frontal gyrus to occipital pole, inferior occipital lobe, and middle occipital lobe. Our work demonstrates the feasibility of high resolution diffusion tensor tractography with sufficient sensitivity to elucidate more anatomical details of the IFOF. And we provides a new framework for subdividing the IFOF for better understanding its functional role in the human brain.
Highlights
The inferior fronto-occipital fasciculus (IFOF) is one of the first major association fiber systems to be recognized and depicted in the human brain (Schmahmann and Pandya, 2007)
There are some natural crossings of the IFOF with other tracts, including the superior longitudinal fasciculus (SLF), arcuate fascicle (AF), inferior longitudinal fasciculus (ILF), and middle longitudinal fascicle (MdLF)
This distinct pathway demonstrated a greater inter-subjects connective variability with a maximum of 40% overlap in its central part. This group of fibers mainly originated from the orbito-frontal cortex, frontal polar cortex, superior frontal gyrus and inferior frontal gyrus, some fibers came from the middle frontal gyrus (12 out of 20 hemispheres)
Summary
The inferior fronto-occipital fasciculus (IFOF) is one of the first major association fiber systems to be recognized and depicted in the human brain (Schmahmann and Pandya, 2007). Neither of them mentioned the connections of the subcomponents to the posterior terminations In another post-mortem dissection study, Martino et al firstly reported new cortical terminations (i.e., postero-basal temporal portions and superior parietal lobe) except as the occipital cortex. They suggested that there were two different subcomponents in the IFOF. The other was a ventral and deep subpart that connected the posterior part of the inferior occipital cortex and the posterior temporo-basal portions with the frontal lobe They failed to identify their cortical terminations within the frontal lobe (Martino et al, 2010). The dissection is limited to be applied in different crossing fiber termination regions
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