Abstract
During word and object recognition, extensive activation has consistently been observed in the left ventral occipito-temporal cortex (vOT), focused around the occipito-temporal sulcus (OTs). Previous studies have shown that there is a hierarchy of responses from posterior to anterior vOT regions (along the y-axis) that corresponds with increasing levels of recognition - from perceptual to semantic processing, respectively. In contrast, the functional differences between superior and inferior vOT responses (i.e. along the z-axis) have not yet been elucidated. To investigate, we conducted an extensive review of the literature and found that peak activation for reading varies by more than 1 cm in the z-axis. In addition, we investigated functional differences between superior and inferior parts of left vOT by analysing functional MRI data from 58 neurologically normal skilled readers performing 8 different visual processing tasks. We found that group activation in superior vOT was significantly more sensitive than inferior vOT to the type of task, with more superior vOT activation when participants were matching visual stimuli for their semantic or perceptual content than producing speech to the same stimuli. This functional difference along the z-axis was compared to existing boundaries between cytoarchitectonic areas around the OTs. In addition, using dynamic causal modelling, we show that connectivity from superior vOT to anterior vOT increased with semantic content during matching tasks but not during speaking tasks whereas connectivity from inferior vOT to anterior vOT was sensitive to semantic content for matching and speaking tasks. The finding of a functional dissociation between superior and inferior parts of vOT has implications for predicting deficits and response to rehabilitation for patients with partial damage to vOT following stroke or neurosurgery.
Highlights
Many functional imaging studies of reading have reported activation in the left ventral occipito-temporal cortex, centred around the middle part of the left occipito-temporal sulcus
This study investigated whether activation and connectivity differed, according to experimental task or stimuli, in superior and inferior parts of ventral occipito-temporal cortex
An extensive review of the literature did not generate any clear hypotheses for a functional dissociation in these regions it was clear that the co-ordinates of peak ventral occipito-temporal cortex (vOT) activation vary considerably in the Z-axis
Summary
Many functional imaging studies of reading have reported activation in the left ventral occipito-temporal (vOT) cortex, centred around the middle part of the left occipito-temporal sulcus. As the same region is activated during many tasks other than reading, it appears to play a more general role in integrating visual inputs with the language system (see Price, 2012 for review). Given the size of the vOT region, and variability in where reading activation is reported, there are likely to be multiple subdivisions with dissociable functions. This has already been documented in the posterior-to-anterior direction (Y-axis) (Lerma-Usabiaga et al, 2018; Seghier and Price, 2011; Vinckier et al, 2007), and the lateral-medial direction (x-axis (Gao et al, 2017), but not in the inferior-superior direction. The aim of current study was to investigate what drives variation in activation along the Z-axis (superior versus inferior)
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