Evidence for the functional and structural differentiation of the inferior fronto-occipital fasciculus using DTI tractography

• Author / Creator

  Rollans, Claire

• The inferior fronto-occipital fasciculus (IFOF), a major ventral white matter pathway, has been shown to be a crucial component of semantic (Moritz-Gasser, Herbet & Duffau, 2013) and lexical/orthographic (Vandermosten, Boets, Polemans, Sunaert, Wouters & Ghesquière, 2012) processing. However, recent anatomical studies of the brain have revealed at least two differentiable components of the IFOF: a dorsal component projecting from the frontal lobe to the superior parietal lobule, and a ventral component connecting the frontal lobe with the inferior occipital gyrus and posterior temporal lobe (Martino, Brogna, Robles, Vergani & Duffau, 2010). We have replicated this anatomical division using a new deterministic tractography protocol in DTI Studio, and found this protocol to have high inter-rater reliability (ICC > 0.9). Furthermore, we provided the first evidence of a functional distinction between these two components. We compared diffusion measures (e.g., fractional anisotropy [FA], an indirect measure of white matter microstructural integrity) with reaction times on five different reading tasks: basic naming of pure exception words, regular words, and mixed exception/regular words, and go/no-go tasks involving either pseudohomophone or nonword foils. We found a clear functional divide in the left IFOF, whereby dorsal FA was specifically correlated with performance on tasks that required higher levels of visual attention and response selection (go/no-go and mixed naming tasks), while ventral FA was more broadly correlated with naming performance. This demonstrates that the anatomical distinction described by Martino et al. (2010) is indeed mirrored by a functional distinction, and suggests that future investigations of neuroanatomical models of reading and speech production should consider the dorsal and ventral IFOF as separate entities.

• Subjects / Keywords

  • Inferior fronto-occipital fasciculus
  • Naming
  • DTI
  • Go/no-go
  • Tractography

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3N58CX05

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.