Abnormal development of sensory-motor, visual temporal and parahippocampal cortex in children with learning disabilities and borderline intellectual functioning

Abstract

Borderline intellectual functioning (BIF) is a condition characterized by an intelligence quotient (IQ) between 70 and 85. BIF children present with cognitive, motor, social, and adaptive limitations that result in learning disabilities and are more likely to develop psychiatric disorders later in life. The aim of this study was to investigate brain morphometry and its relation to IQ level in BIF children. Thirteen children with BIF and 14 age- and sex-matched typically developing (TD) children were enrolled. All children underwent a full IQ assessment (WISC-III scale) and a magnetic resonance (MR) examination including conventional sequences to assess brain structural abnormalities and high resolution 3D images for voxel-based morphometry analysis. To investigate to what extent the group influenced gray matter (GM) volumes, both univariate and multivariate generalized linear model analysis of variance were used, and the varimax factor analysis was used to explore variable correlations and clusters among subjects. Results showed that BIF children, compared to controls have increased regional GM volume in bilateral sensorimotor and right posterior temporal cortices and decreased GM volume in the right parahippocampal gyrus. GM volumes were highly correlated with IQ indices. The present work is a case study of a group of BIF children showing that BIF is associated with abnormal cortical development in brain areas that have a pivotal role in motor, learning, and behavioral processes. Our findings, although allowing for little generalization to the general population, contribute to the very limited knowledge in this field. Future longitudinal MR studies will be useful in verifying whether cortical features can be modified over time even in association with rehabilitative intervention.

Keywords: borderline intellectual functioning (BIF); brain maturation; learning disabilities; motor development; voxel-based morphometry (VBM).

FIGURE 1

Results of factor analysis on ROI variables and IQ scores. Biplots of factor scores by group (A) and related multivariate analysis (B,C). Explained variances and factor pattern were reported on (D). LSM1, left sensorimotor cortex; RPTC, right posterior temporal cortex; RSM1, right sensorimotor cortex; RPH, right parahippocampus; FSIQ, full scale IQ; PIQ, performance IQ; VIQ, verbal IQ; VCI, verbal comprehension index; POI, perceptual organization index; FDI, freedom from distractibility index; PSI, processing speed index.

FIGURE 2

VBM results. Direct comparison between BIF and TD. In red squares, cortical areas confirmed by the univariate test for group effect (see “Materials and Methods” for further details and statistical thresholds). ROI, region of interest; LPC, left posterior cingulate; LSM1, left sensorimotor cortex; RPTC, right posterior temporal cortex; RSM1, right sensorimotor cortex; RMOC, right middle occipital cortex; LMOC, left middle occipital cortex; and RPH, right parahippocampus.