Abstract
The existence of the superior fronto-occipital fasciculus (SFOF) in the human brain remains controversial. The aim of the present study was to clarify the existence, course, and terminations of the SFOF. High angular diffusion spectrum imaging (DSI) analysis was performed on six healthy adults and on a template of 842 subjects from the Human Connectome Project. To verify tractography results, we performed fiber microdissections of four post-mortem human brains. Based on DSI tractography, we reconstructed the SFOF in the subjects and the template from the Human Connectome Project that originated from the rostral and medial parts of the superior and middle frontal gyri. By tractography, we found that the fibers formed a compact fascicle at the level of the anterior horn of the lateral ventricle coursing above the head of caudate nucleus, medial to the corona radiate and under the corpus callosum (CC), and terminated at the parietal region via the lower part of the caudate nucleus. We consider that this fiber bundle observed by tractography is the SFOF, although it terminates mainly at the parietal region, rather than occipital lobe. By contrast, we were unable to identify a fiber bundle corresponding to the SFOF in our fiber dissection study. Although we did not provide definite evidence of the SFOF in the human brain, these findings may be useful for future studies in this field.
Highlights
The superior fronto-occipital fasciculus (SFOF) was first described as a longitudinal ridge in autopsies of acallosal patients by Eichler (1878)
After removing the whole thalamus, we observed a few fibers coming from the parietal region, which had a close relationship to the stria terminalis (ST; Figure 2F)
If the diffusion spectrum imaging (DSI) tractographic SFOF really exist, based on cortical parcellation (Desikan et al, 2006), we found that the SFOF would originate from the rostral and medial parts of the superior and middle frontal gyrus (MFG) (Brodmann area [BA] 8, 9 and 10), the fibers formed a compact fascicle at the level of the anterior horn of the lateral ventricle coursing above the head of caudate, medial to the corona radiate and under the corpus callosum (CC), and terminated at the superior parietal lobe (SPL) and precuneus (BA area 7) via the lower part of the caudate
Summary
The superior fronto-occipital fasciculus (SFOF) was first described as a longitudinal ridge in autopsies of acallosal patients by Eichler (1878). The prevailing consensus proposed by Dejerine is that the SFOF is a distinct 2–3 mm wide white matter located medial to the corona radiate, superolateral to the caudate nucleus, and ventrolateral to the corpus callosum (CC), and which interconnects the frontal and occipital lobes as association fibers. Using isotope tract-tracing in the monkey brain, Schmahmann and Pandya confirmed that the SFOF courses above the caudate nucleus, medial to the corona radiate, and lateral and ventral to the CC, connects the parietal lobe with the frontal lobe, and plays a role in the rapid top-down modulation of visual processing and spatial aspects of cognitive processing (Bar et al, 2006; Schmahmann and Pandya, 2007). Despite being well described in human, the inferior fronto-occipital fasciculus (IFOF) does not exist in the monkey brain (Schmahmann et al, 2007; Forkel et al, 2014)
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