Researchers have long studied the biological basis for intelligence and have found increasing evidence relating high performance on IQ tests to the coordination of multiple brain regions. However, no direct evidence has been provided from the perspective of brain networks. In this study, we used fiber tracking method based on diffusion tensor imaging (DTI) to construct anatomical brain networks for each individual of 79 healthy young adults and calculated the network properties using a graph theoretical method. Our results showed topological properties that were quite comparable with the findings of previous human brain network studies. Moreover, we showed significant correlations between IQ scores and network properties across all subjects. Specifically, higher intelligence scores corresponded to a shorter characteristic path length and a higher global efficiency of the brain networks, indicating a more efficient information transfer in the brain. To the best of our knowledge, this is the first study that investigated the relationship between intelligence and the brain anatomical network utilizing the DTI method, which not only supports the concept that complex brain network topology parameters have cognitive significance but also suggests that a more efficient brain structural organization may be an important biological basis for higher intelligence. We further investigated 15 mental retardation (MR) patients, comparing them with normal controls using different methods based on DTI. In MR patients, we found decrease of white matter integrity in multiple brain regions as well as longer characteristic path length and lower global efficiency of brain networks associated with their extremely lower IQ scores. Our findings further suggest that decreased efficiency of brain structural organization may contribute to their poor intellectual performance of MR patients. Finally, combining with DTI method, we performed a genetic study of intelligence, which focused on COMT Val158Met. All participants including the 79 healthy subjects and the 15 MR patients were divided into two groups according to their genotypes on Val158Met: carriers of the Met allele and homozygous for the Val allele. Although no significant differences of general IQ scores, fractional anisotropy values derived from DTI as well as properties of brain networks were observed between two groups, the correlation between white matter integrity and IQ scores were found to be different between g...
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