Children With Dyscalculia Show Hippocampal Hyperactivity During Symbolic Number Perception

Abstract

Dyscalculia is a learning disability affecting the acquisition of arithmetical skills in children with normal intelligence and age-appropriate education. Two hypotheses attempt to explain the main cause of dyscalculia. The first hypothesis suggests that a problem with the core mechanisms of perceiving (non-symbolic) quantities is the cause of dyscalculia (core deficit hypothesis), while the alternative hypothesis suggests that dyscalculics have problems only with the processing of numerical symbols (access deficit hypothesis). In the present study, the symbolic and non-symbolic numerosity processing of typically developing children and children with dyscalculia were examined with functional magnetic resonance imaging (fMRI). Control (n = 15, mean age: 11.26) and dyscalculia (n = 12, mean age: 11.25) groups were determined using a wide-scale screening process. Participants performed a quantity comparison paradigm in the fMRI with two number conditions (dot and symbol comparison) and two difficulty levels (0.5 and 0.7 ratio). The results showed that the bilateral intraparietal sulcus (IPS), left dorsolateral prefrontal cortex (DLPFC) and left fusiform gyrus (so-called "number form area") were activated for number perception as well as bilateral occipital and supplementary motor areas. The task difficulty engaged bilateral insular cortex, anterior cingulate cortex, IPS, and DLPFC activation. The dyscalculia group showed more activation in the left orbitofrontal cortex, left medial prefrontal cortex, and right anterior cingulate cortex than the control group. The dyscalculia group showed left hippocampus activation specifically for the symbolic condition. Increased left hippocampal and left-lateralized frontal network activation suggest increased executive and memory-based compensation mechanisms during symbolic processing for dyscalculics. Overall, our findings support the access deficit hypothesis as a neural basis for dyscalculia.

Keywords: dyscalculia; functional magnetic resonance imaging; hippocampus; learning disabilities; number sense.

FIGURE 1

(A) Experimental quantity comparison paradigm that includes symbolic comparison and dot comparison condition. Each trial lasted for 2 s and intertrial intervals (ITI) were 2, 4, or 6 s. (B) Behavioral data. Graphs show the percentage of correct responses and reaction time results.

FIGURE 2

The fMRI group analysis results depicting significant activations. (A) The dorsolateral prefrontal, bilateral parietal, and occipital cortex activations related to the main effect of number sense. (B) The anterior cingulate and bilateral insular cortex activations related to the main effect of difficulty (cluster-extent corrected for p < 0.05 for all maps). IPL, inferior parietal lobe; DLPFC, dorsolateral prefrontal cortex; OC, occipital cortex; ACC, anterior cingulate cortex; L, left; R, right; A, anterior; P, posterior.

FIGURE 3

The fMRI group analysis results depicting significant activations. (A) The anterior cingulate, medial prefrontal, and orbitofrontal cortex activations related to the main effect of the group. (B) The hippocampus activations related to the group-task interaction. Percent signal change graphs that show differences of BOLD signal value extracted from hippocampus ROI (cluster-extent corrected for p < 0.05). ACC, anterior cingulate cortex; mPFC, medial prefrontal cortex; OPFC, orbitofrontal cortex; L, left; R, right; A, anterior; P, posterior.