Twomey, T; (2013) Ventral occipito-temporal cortex function and anatomical connectivity in reading. Doctoral thesis (PhD), UCL (University College London).

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Abstract

Previous functional neuroimaging studies of reading in skilled readers, acquired dyslexia and developmental dyslexia have all shown that the left ventral occipito-temporal cortex (vOT) is involved in visual word recognition. Specifically, a region in the left posterior occipito-temporal sulcus lateral to fusiform gyrus and medial to inferior temporal gyrus has been reported to play an important role. However, the precise functional contribution of this area in reading is yet to be fully explored. In this thesis, I empirically evaluated a claim that vOT responds not only to bottom-up processing demands of the visual stimuli but is also influenced by automatic, top-down non-visual processing demands, as proposed by the Interactive Account of vOT functioning. The first part of this thesis investigated the functional properties of vOT during reading, using functional magnetic resonance imaging. In the first project, the top-down influences on vOT were investigated, teasing apart visual and non-visual properties of written stimuli. In the second project, using the Japanese orthography I disentangled a word’s lexical frequency from the frequency of its visual form – an important distinction for understanding the neural information processing in regions engaged by reading and further explored the interactive nature of the vOT responses. The second part then investigated the anatomical basis of these functional interactions between vOT and other cortical regions. I used diffusion-weighted magnetic resonance imaging and tractography, the only method currently available to identify and measure white matter fibre pathways non-invasively and in vivo. My research has demonstrated that vOT integrates bottom-up visual information and top-down predictions from regions encoding non-visual attributes of the stimulus in an interactive fashion. It also illustrated the putative anatomical basis for functional connectivity during reading, which is consistent with the parallel cortical visual pathways seen in other primates. Altogether, the results provide strong support for the Interactive Account.

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