An fMRI study of magnitude comparison and exact addition in children

Abstract

By contrast to the adult literature, in which a consistent parietofrontal network for number processing has been identified, the data from studies of number processing in children have been less consistent, probably due to differences in study design and control conditions. Number processing was examined using functional magnetic resonance imaging in 18 right-handed children (8-12 years) from the Cape Coloured community in Cape Town, South Africa, using Proximity Judgment and Exact Addition (EA) tasks. The findings were consistent with the hypothesis that, as in adults, the anterior horizontal intraparietal sulcus (HIPS) plays a major role in the representation and manipulation of quantity in children. The posterior medial frontal cortex, believed to be involved in performance monitoring in more complex arithmetic manipulations in adults, was extensively activated even for relatively simple symbolic number processing in the children. Other areas activated to a greater degree in the children included the left precentral sulcus, which may mediate number knowledge and, for EA, the head of the caudate nucleus, which is part of a fronto-subcortical circuit involved in the behavioral execution of sequences. Two regions that have been linked to number processing in adults - the angular gyrus and posterior superior parietal lobule - were not activated in the children. The data are consistent with the inference that although the functional specialization of the anterior HIPS may increase as symbolic number processing becomes increasingly automatic, this region and other elements of the parietofrontal network identified in adults are already reliably and robustly activated by middle childhood.

Figure 1

Schematic of task design showing the format and timing for blocks of (a) Exact Addition trials, and (b) control trials. The same format and timing was used for the Proximity Judgment task.

Figure 2

Activation maps show greater activity during Proximity Judgment compared to the control task in the posterior medial frontal cortex (pMFC) that extends bilaterally into the superior frontal sulci, right anterior horizontal intraparietal sulcus (HIPS), right posterior HIPS, a large bilateral activation in the precuneus that extends continuously into the left posterior HIPS and right cuneus, right parieto-occipital sulcus, left precentral sulcus, right and left middle frontal gyrus, right tail of caudate and left head of caudate, and right and left anterior insula.

Figure 3

Activation maps show greater activity during Exact Addition compared to the control task in the left superior frontal sulcus, posterior medial frontal cortex, right central sulcus, left anterior and posterior HIPS, right posterior HIPS, bilateral precuneus, left precentral sulcus, bilateral activations in the dorsolateral prefrontal cortex, left cingulate gyrus, right and left head of caudate, right thalamus, right anterior insula, right and left deep cerebellar nuclei, and right cerebellar cortex.