Additional evidence for left hemispheric lateralization in a

Additional evidence for left hemispheric lateralization in adults was also reported in a cross-cultural fMR-A study by Holloway et al. (2012). This study revealed a striking hemispheric difference in IPS activation in response to the presentation of Arabic numerals and Chinese ideographs. Two groups were used: a bilingual group capable of reading Chinese and Arabic numerals, and a control group capable of reading Arabic but not Chinese numerals. The symbol 6 was presented repeatedly on a screen to induce Phos-tag Biotin (decrease in neuronal response) in number-sensitive regions. This stream of 6\'s was interspersed with the presentation of numerical deviants, which differed in numerical ratio from 6. The prediction was that deviants that differed more from the adapted numeral (have a smaller ratio) would be associated with a larger signal recovery in the adapted neuronal response compared to numerals that are close to the adaptation numeral (have a larger ratio). Results demonstrated a significant ratio-dependent signal recovery in the left IPS in response to Arabic numerals across both the bilingual and control groups. However, Chinese ideographs, with which participants were less familiar, elicited a signal recovery exclusively in the right IPS of Chinese participants. In this study both groups had extensive experience with Arabic numerals and exhibited ratio-dependent signal recovery in the left IPS for this condition. The Chinese bilingual group had experience with the Chinese symbols, however, they were less familiar with these symbols than with the Arabic numerals and did not use them routinely in the context of calculation. Therefore, the result of the right lateralized ratio-dependent recovery effect in the bilingual group for Chinese symbols, combined with the left-lateralized effect in the left IPS for Arabic numerals, is suggestive of experience dependent lateralization in the way the parietal lobe of adults represents symbolic numerical formats. Although neural activation patterns associated with the processing of numerical symbols have been studied in adults, symbolic numerical processing is the outcome of a trajectory of learning and experience. Studies with adult populations are not well suited to explain how representations of symbolic numerical magnitude – such as their fluidity and automaticity – change over the course of learning and development. Developmental neuroimaging studies have recently provided additional evidence for hemispheric lateralization in association with the representation of symbolic numerical magnitude (e.g., Bugden et al., 2012; Emerson and Cantlon, 2014). For instance, a longitudinal study with 4- to 9-year old children revealed a significant correlation between two time points separated by two years in right IPS activation (right IPS activation at time point 1 correlated with right IPS activation at time point 2). The left IPS, however, demonstrated an age related correlation between brain activation and children\'s numerical discrimination performance (i.e., acuity) as measured by the numerical distance effect (Emerson and Cantlon, 2014).
Material and methods
Results
Discussion A growing body of research has explored the neural correlates associated with the representation of symbolic numerical magnitude in adults (for reviews see Dehaene et al., 2003; Nieder and Dehaene, 2009). While much insight has been gained into the brain circuitry associated with symbolic number processing in adults, comparatively little is known about the way the human brain constructs rich semantic representations of numerical symbols over developmental time. The scarce number of developmental studies existing to date have demonstrated a significant shift of the functional neuroanatomy from a greater reliance on prefrontal regions in children to a larger engagement of parietal regions in older children and adults (Ansari et al., 2005; Cantlon et al., 2009; Kaufmann et al., 2006; for a review see Vogel and Ansari, 2012).