Abstract
The intraparietal sulcus (IPS) in the posterior parietal cortex (PPC) is well-known as an interface for sensorimotor integration in visually guided actions. However, our understanding of the human neural network between the IPS and the cortical visual areas has been devoid of anatomical specificity. We here identified a distinctive association fiber tract “IPS-FG” to connect the IPS areas and the fusiform gyrus (FG), a high-level visual region, by white matter dissection and tractography. The major fiber bundles of this tract appeared to arise from the medial bank of IPS, in the superior parietal lobule (SPL), and project to the FG on the ventral temporal cortex (VTC) in post-mortem brains. This tract courses vertically at the temporo-parieto-occipital (TPO) junction where several fiber tracts intersect to connect the dorsal-to-ventral cortical regions, including the vertical occipital fasciculus (VOF). We then analyzed the structural connectivity of this tract with diffusion-MRI (magnetic resonance imaging) tractography. The quantitative tractography analysis revealed the major streamlines of IPS-FG interconnect the posterior IPS areas (e.g., IP1, IPS1) with FG (e.g., TF, FFC, VVC, PHA2, PIT) on the Human Connectome Project multimodal parcellation atlas (HCP MMP 1.0). Since the fronto-parietal network, including the posterior IPS areas, is recruited by multiple cognitive demands, the IPS-FG could play a role in the visuomotor integration as well as the top-down modulation of various cognitive functions reciprocally.
Highlights
Vision-guided actions depend on the visual information to finely coordinate motor responses of the eye and hand to perform accurate, rapid, and tuned m ovements[1,2]
This tract interconnects the intraparietal sulcus (IPS) areas with the fusiform gyrus (FG) vertically in parallel between the arcuate fasciculus (AF) and the vertical occipital fasciculus (VOF). It courses in the temporo-parieto-occipital (TPO) junction, where several fiber tracts intersect in a complex way, including the superior longitudinal fascicle (SLF), the arcuate fasciculus (AF), the middle longitudinal fasciculus (MdLF), the inferior longitudinal fasciculus (ILF), the inferior fronto-occipital fasciculus (IFOF), and the V OF8,9
During the dissection of VOF, we happened to identify a distinct fiber tract described as “IPS-FG”, which appeared to connect the areas around the IPS (IPS areas) and the ventral temporal cortex (VTC) (Fig. 1A,B)
Summary
Vision-guided actions (e.g., reaching, grasping, and object manipulation) depend on the visual information to finely coordinate motor responses of the eye and hand to perform accurate, rapid, and tuned m ovements[1,2]. Since the lesions to the intraparietal sulcus (IPS) and the superior parietal lobule (SPL) in the posterior parietal cortex (PPC) result in the neurological deficit called Balint’s syndrome (optic ataxia)[2,3,4], the IPS is considered as a hub for sensorimotor integration in visually guided actions, including eye–hand coordination. We identified a distinct association fiber tract described as “IPS-FG” that connects the IPS areas and the FG in the post-mortem brain dissection in four hemispheres (two right and left sides, respectively). This tract interconnects the IPS areas with the FG vertically in parallel between the arcuate fasciculus (AF) and the vertical occipital fasciculus (VOF). We showed the IPS-FG overlaps with the border of the TP-SPL by t ractography[9,10,11]
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