Abstract
FMRI-studies are mostly based on a group study approach, either analyzing one group or comparing multiple groups, or on approaches that correlate brain activation with clinically relevant criteria or behavioral measures. In this study we investigate the potential of fMRI-techniques focusing on individual differences in brain activation within a test-retest reliability context. We employ a single-case analysis approach, which contrasts dyscalculic children with a control group of typically developing children. In a second step, a support-vector machine analysis and cluster analysis techniques served to investigate similarities in multivariate brain activation patterns. Children were confronted with a non-symbolic number comparison and a non-symbolic exact calculation task during fMRI acquisition. Conventional second level group comparison analysis only showed small differences around the angular gyrus bilaterally and the left parieto-occipital sulcus. Analyses based on single-case statistical procedures revealed that developmental dyscalculia is characterized by individual differences predominantly in visual processing areas. Dyscalculic children seemed to compensate for relative under-activation in the primary visual cortex through an upregulation in higher visual areas. However, overlap in deviant activation was low for the dyscalculic children, indicating that developmental dyscalculia is a disorder characterized by heterogeneous brain activation differences. Using support vector machine analysis and cluster analysis, we tried to group dyscalculic and typically developing children according to brain activation. Fronto-parietal systems seem to qualify for a distinction between the two groups. However, this was only effective when reliable brain activations of both tasks were employed simultaneously. Results suggest that deficits in number representation in the visual-parietal cortex get compensated for through finger related aspects of number representation in fronto-parietal cortex. We conclude that dyscalculic children show large individual differences in brain activation patterns. Nonetheless, the majority of dyscalculic children can be differentiated from controls employing brain activation patterns when appropriate methods are used.
Highlights
During the last two decades, images of the working brain have led to great hopes with respect to the clinical applicability of fMRI
Out of a sample of 40 children (20 girls, 20 boys) in the age range from 6 years and 5 months to 10 years and 5 months with below average performance in diagnostic tests of number processing and calculation, who participated in a larger training study, we selected all children who were diagnosed with developmental dyscalculia and who did not move more than the equivalent of 1.5 voxels (5.25 mm) during the course of acquisition
Even if the two groups presented with no significant differences in reaction time, we would like to point out that the children in the Developmental dyscalculia (DD) group are diagnosed with developmental dyscalculia on the basis of a much more elaborate test for dyscalculia
Summary
During the last two decades, images of the working brain have led to great hopes with respect to the clinical applicability of fMRI. ICCs of fMRI results reported in child studies usually are below 0.33 [20] This level of reliability is not sufficient for clinical purposes, but some suggestions have been made for improvement, such as increasing the number of observations and optimizing the fMRItask design at the level of image acquisition as well as improving data analysis techniques at the level of preprocessing [19]. Tests that are not predictive for a disorder are usually removed from a diagnostic battery Applying these standards to fMRI, e.g. for the assessment of developmental dyscalculia, is challenging because one needs to know how to search and where to search in the brain for the possible detection of different patterns of activation. Hierarchical cluster analyses using data of each paradigm separately and in a conjoint way will be carried out to study global similarities in extended brain activation patterns between individuals
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