Article

Functional Imaging of Numerical Processing in Adults and 4-y-Old Children

Department of Psychological and Brain Sciences, Duke University, Durham, North Carolina, USA.
PLoS Biology (Impact Factor: 9.34). 06/2006; 4(5):e125. DOI: 10.1371/journal.pbio.0040125
Source: PubMed

ABSTRACT

Adult humans, infants, pre-school children, and non-human animals appear to share a system of approximate numerical processing for non-symbolic stimuli such as arrays of dots or sequences of tones. Behavioral studies of adult humans implicate a link between these non-symbolic numerical abilities and symbolic numerical processing (e.g., similar distance effects in accuracy and reaction-time for arrays of dots and Arabic numerals). However, neuroimaging studies have remained inconclusive on the neural basis of this link. The intraparietal sulcus (IPS) is known to respond selectively to symbolic numerical stimuli such as Arabic numerals. Recent studies, however, have arrived at conflicting conclusions regarding the role of the IPS in processing non-symbolic, numerosity arrays in adulthood, and very little is known about the brain basis of numerical processing early in development. Addressing the question of whether there is an early-developing neural basis for abstract numerical processing is essential for understanding the cognitive origins of our uniquely human capacity for math and science. Using functional magnetic resonance imaging (fMRI) at 4-Tesla and an event-related fMRI adaptation paradigm, we found that adults showed a greater IPS response to visual arrays that deviated from standard stimuli in their number of elements, than to stimuli that deviated in local element shape. These results support previous claims that there is a neurophysiological link between non-symbolic and symbolic numerical processing in adulthood. In parallel, we tested 4-y-old children with the same fMRI adaptation paradigm as adults to determine whether the neural locus of non-symbolic numerical activity in adults shows continuity in function over development. We found that the IPS responded to numerical deviants similarly in 4-y-old children and adults. To our knowledge, this is the first evidence that the neural locus of adult numerical cognition takes form early in development, prior to sophisticated symbolic numerical experience. More broadly, this is also, to our knowledge, the first cognitive fMRI study to test healthy children as young as 4 y, providing new insights into the neurophysiology of human cognitive development.

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    • "However, the precise nature of right and left IPS engagement and the mechanisms underlying developmental changes in the left IPS in the present work remain opaque; future research is required. Moreover, while previous developmental neuroimaging studies have found a shift from prefrontal regions in children to parietal regions in adults (Ansari et al., 2005; Cantlon et al., 2009; Holloway and Ansari, 2010; Kaufmann et al., 2005, 2006), the present study did not reveal a negative correlation between chronological age and signal recovery in the prefrontal cortex. While the absence of an effect is difficult to interpret, this null result may nevertheless indicate that previously observed frontal activations in number comparison tasks may not be related to developmental changes of symbolic numerical magnitude representation per se or the mapping between numerical magnitudes and their symbolic referents . "
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