Anatomic dissection of the inferior fronto-occipital fasciculus revisited in the lights of brain stimulation data.

The consensus is that the IFOF connects the ventral occipital cortex with the inferior frontal and fronto-orbital cortices.

“the IFOF connects the ventral occipital cortex with the inferior frontal and fronto-orbital cortices”

There is some inter-individual variability in the tract projections.

“Previous dissection work indicates that there is some inter-individual variability in the tract projections (Martino et al., 2010).”

The IFOF and UF are clearly distinct at the level of the stem and can be separated by a notable cleavage line.

“However, they are clearly distinct at the level of the stem and can be separated by a notable cleavage line (Curran, 1909; Kier et al., 2004; Martino et al., 2010; Sarubbo et al., 2013).”

The superior occipital gyrus was not significant as a termination territory.

“In contrast, the superior occipital gyrus was not significant as a termination territory (Martino et al., 2010).”

Superior parietal IFOF terminations were observed in the majority of subjects, consistent with Martino et al. (2010), and less frequently in the angular gyrus, in contrast to Caverzasi et al. (2014).

“We observed superior parietal IFOF terminations in the majority of the subjects consistent with dissection [Martino et al. (2010) reported parietal connections in 9 out of 14 hemispheres], and less frequently in the angular gyrus in contrast to Caverzasi et al. (2014) who reported it in 100% of subjects.”

Post-mortem dissection studies have noted considerable overlap between the infero-superior course of the IFOF and antero-posterior course of the arcuate fasciculus near the inferior and middle frontal regions.

“Post-mortem dissection studies have noted considerable overlap between the infero-superior course of the IFOF and antero-posterior course of the arcuate fasciculus near the inferior and middle frontal regions (Martino et al., 2010; Sarubbo et al., 2013).”

Projections to the inferior occipital gyrus were observed, twice less in the left than in the right hemisphere, though reported in all subjects in a dissection study (Martino et al., 2010).

“Projections to the inferior occipital gyrus were observed, twice less in the left than in the right hemisphere, though it was reported in all subjects in a dissection study (Martino et al., 2010).”

Projections to the lingual gyrus were observed in almost all subjects, consistent with Caverzasi et al. (2014), but Martino et al. (2010) reported no projections to the lingual gyrus and considered them part of the optic radiations.

“Projections to the lingual gyrus were observed in almost all subjects consistent with Caverzasi et al. (2014), however, Martino et al. (2010) reported no projections to the lingual gyrus and instead considered them as part of the optic radiations.”

In the temporal lobe, the IFOF projects to the superior and middle temporal gyri and to a lesser extent to the fusiform gyrus, confirming dissection studies.

“In the temporal lobe, the IFOF projects to the superior and middle temporal gyri and to a lesser extent to the fusiform gyrus, confirming dissection studies (Crosby et al., 1962; Martino et al., 2010).”

There is converging evidence for the existence of fronto-parietal connections for the IFOF from post-mortem and tractography studies.

“There is converging evidence for the existence of fronto-parietal connections for the IFOF from post-mortem (Curran, 1909; Martino et al., 2010) and tractography studies (Mori et al., 2005; Caverzasi et al., 2014).”

The study consistently observed a cleavage zone within the ventral portion of the external capsule between the UF fibers turning anteriorly and inferiorly to the temporal lobe and the IFOF fibers going deeply and dorsally.

“As such, we consistently observed a cleavage zone within the ventral portion of the external capsule between the UF fibers turning anteriorly and inferiorly to the temporal lobe (including the superior, middle and inferior temporal gyri posterior to the temporal pole) and the IFOF fibers going deeply and dorsally (Martino et al., 2010; Sarubbo et al., 2013).”