N-acetylaspartate concentration in corpus callosum is positively correlated with intelligence in adolescents.

The corpus callosum is the largest white matter bundle in the brain and integrates inter-hemispheric cortices during sensory-motor and high-order cognitive processes. The aim of the present study was to investigate the associations between the metabolite concentrations in the corpus callosum and intelligence among adolescents. Thirty male adolescents aged between 14 and 16 years were included into the study. We measured the intelligence quotient (IQ) scores of the subjects by using the Wechsler Intelligence Scale for Children-Revised (verbal, performance and full-scale IQ) test. We used proton MR spectroscopy to measure the absolute concentrations of N-acetylasparate (NAA), creatine (Cr) and choline (Cho) in the genu, midbody and isthmus/splenium regions of the corpus callosum. We also measured the whole brain parenchymal size and used it as a confounding factor in the statistical analyses. We assessed the correlations between neurometabolite concentrations and verbal, performance and full-scale IQ scores. We found a significant positive correlation between the whole brain parenchymal size and the full-scale IQ scores. And, the NAA concentration in the isthmus/splenium region was positively correlated with the performance IQ and full-scale IQ scores. NAA is a marker of neuro/axonal integrity. NAA concentration in white matter is related to the structural and functional integrity of axonal fibers. The positive correlation of the IQ scores with the NAA concentrations in the isthmus/splenium region indicates that more efficient inter-hemispheric data transfer between parieto-occipital cortices may enhance intellectual performance.