Abstract
The adult brain contains cortical areas thought to be specialized for the analysis of numbers (the putative number form area, NFA) and letters (the visual word form area, VWFA). Although functional development of the VWFA has been investigated, it is largely unknown when and how the NFA becomes specialized and connected to the rest of the brain. One hypothesis is that NFA and VWFA derive their special functions through differential connectivity, but the development of this differential connectivity has not been shown. Here, we mapped the resting state connectivity of NFA and VWFA to the rest of the brain in a large sample (n = 437) of individuals (age 3.2–21 years). We show that within NFA-math network and within VWFA-reading network the strength of connectivity increases with age. The right NFA is significantly connected to the right intraparietal cortex already at the earliest age tested (age 3), before formal mathematical education has begun. This connection might support or enable an early understanding of magnitude or numerosity In contrast, the functional connectivity from NFA to the left anterior intraparietal cortex and to the right dorsolateral prefrontal cortex is not different from the functional connectivity of VWFA to these regions until around 12–14 years of age. The increase in connectivity to these regions was associated with a gradual increase in mathematical ability in an independent sample. In contrast, VWFA connects significantly to Broca’s region around age 6, and this connectivity is correlated with reading ability. These results show how the differential connectivity of the networks for mathematics and reading slowly emerges through years of training and education.
Highlights
Over the last decades several fMRI studies have investigated the functional organization of the occipito-temporal cortex in humans
We identified all voxels in the brain that were significantly more correlated with number form area (NFA) than with visual word form area (VWFA) [x = −46, y = −59, z = −15, coordinates based on the same paper (Grotheer et al, 2016b)]
By contrasting the connectivity of NFA and VWFA we identified regions that were specific for NFA and subtracted away possible confounding correlations from global fluctuations, correlation between NFA and VWFA, and noise
Summary
Over the last decades several fMRI studies have investigated the functional organization of the occipito-temporal cortex in humans. Several brain regions in the occipito-temporal cortex have been defined by selectivity for object shape, or by selectivity for specific categories, such as bodies (fusiform body areas, Schwarzlose et al, 2005), faces (fusiform face area, Kanwisher et al, 1997), and places (parahippocampal place area, Epstein and Kanwisher, 1998). The visual word form area (VWFA) is an area in the left occipitotemporal cortex that consistently responds more to letters and words than to other stimuli. The tuning of VWFA to its preferred stimuli seems to be a prolonged process, with response to words stabilizing at around 12 years of age (BenShachar et al, 2011). There is no consensus about the role of this area in word-reading, it must be said that its specificity has been debated (Price and Devlin, 2003)
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