Cortical Terminations of the Inferior Fronto-Occipital and Uncinate Fasciculi: Anatomical Stem-Based Virtual Dissection

Abstract

We combined the neuroanatomists’ approach of defining a fascicle as all fibers passing through its compact stem with diffusion-weighted tractography to investigate the cortical terminations of two association tracts, the inferior fronto-occipital fasciculus (IFOF) and the uncinate fasciculus (UF), which have recently been implicated in the ventral language circuitry. The aim was to provide a detailed and quantitative description of their terminations in 60 healthy subjects and to do so to apply an anatomical stem-based virtual dissection, mimicking classical post-mortem dissection, to extract with minimal a priori the IFOF and UF from tractography datasets. In both tracts, we consistently observed more extensive termination territories than their conventional definitions, within the middle and superior frontal, superior parietal and angular gyri for the IFOF and the middle frontal gyrus and superior, middle and inferior temporal gyri beyond the temporal pole for the UF. We revealed new insights regarding the internal organization of these tracts by investigating for the first time the frequency, distribution and hemispheric asymmetry of their terminations. Interestingly, we observed a dissociation between the lateral right-lateralized and medial left-lateralized fronto-occipital branches of the IFOF. In the UF, we observed a rightward lateralization of the orbito-frontal and temporal branches. We revealed a more detailed map of the terminations of these fiber pathways that will enable greater specificity for correlating with diseased populations and other behavioral measures. The limitations of the diffusion tensor model in this study are also discussed. We conclude that anatomical stem-based virtual dissection with diffusion tractography is a fruitful method for studying the structural anatomy of the human white matter pathways.

Prefrontal and parietal correlates of cognitive control related to the adult outcome of attention-deficit/hyperactivity disorder diagnosed in childhood

“…The current finding of reduced orbitofrontal and inferior frontal activation for conflict in probands with persistent ADHD converges with findings from a previous report that linked the persistence of ADHD in adulthood to lower fractional anisotropy in the uncinate and inferior fronto-occipital fasciculi (Shaw et al, 2015), which connect these prefrontal regions to limbic and visual areas, respectively (Hau et al, 2016). Reduced fractional anisotropy in the inferior fronto-occipital tract and decreased inferior frontal activation for cognitive control are consistent findings in adults with a current diagnosis of ADHD (Cubillo et al, 2010, 2011; Konrad et al, 2012; Silk, Vance, Rinehart, Bradshaw, & Cunnington, 2009).…”

Revisiting the Neural Basis of Acquired Amusia: Lesion Patterns and Structural Changes Underlying Amusia Recovery

“…The IFOF is a ventral pathway that runs from its posterior terminations (inferior and middle occipital gyri, parietal lobe) through the external capsule, between the insula and putamen, and connects to multiple temporal (STG/MTG) and frontal (IFG/MFG) areas (Catani et al, 2002; Hau et al, 2016), thereby covering most of the lesion/atrophy areas observed in our NRA patients. Thus, far using diffusion weighted MRI (DW-MRI), amusia has been linked only to the right arcuate fasciculus (Loui et al, 2009), a dorsal pathway connecting the IFG and STG.…”

White matter degeneration profile in the cognitive cortico‐subcortical tracts in Parkinson's disease

“…It has also been shown that in PD patients higher MD in the VLPFC/DLPFC, damage of the thalamic radiations, and decreased FA in SLF correlates with increased global cognitive impairment . Other studies reported lower FA in PD patients versus HCs, specifically in premotor areas, PUT‐CAU complex, substantia nigra, SLF, and inferior fronto‐occipital fasciculus (which connects VLPFC/DLPFC with middle occipital, superior, and middle temporal and superior parietal gyri) . It has been further reported that decreased FA in SLF was actually driven by the PD‐MCI group .…”

“…24,72,74 Other studies reported lower FA in PD patients versus HCs, specifically in premotor areas, 60,61 PUT-CAU complex, 75 substantia nigra, 76 SLF, 24,75,77 and inferior frontooccipital fasciculus 24,77 (which connects VLPFC/DLPFC with middle occipital, superior, and middle temporal and superior parietal gyri). 77,78 It has been further reported that decreased FA in SLF was actually driven by the PD-MCI group. 22,24,79,80 Our results are also in line with previous functional and structural neuroimaging data that showed increased functional activation in PDN patients versus HCs in the prefrontal-CAU loop, whereas the PD-MCI group versus the PDN group displayed reduced activation.…”