General intelligence is a robust predictor of important life outcomes, including educational and occupational attainment, successfully managing everyday life situations, good health and longevity.There are few established associations between general intelligence and any basic structural brain parameters that have a clear functional meaning.
Cognitive information-processing speed, a well-replicated correlate of intelligence, has long been hypothesised as an intermediate phenotype between the brain and intelligence.Well- connected white matter may allow for faster, more efficient information processing within widespread brain networks responsible for good cognitive functioning.
Diffusion tensor magnetic resonance imaging (DT-MRI) is the method of choice for assessing brain white matter tract integrity in vivo. It quantifies the degree to which the diffusion of water molecules is directionally restricted in the environment of the highly structured axonal tracts that constitute intact white matter. Good integrity mean efficient transmission of signals. White matter tract integrity, as measured by DT-MRI, is a global property of the brain, and is thought to be proxy for processing speed.
This large study ( 420 individuals) measured three biomarkers. 1. Fractional anisometry 2.T1: This is related to tissue water content, with increased T1 being potentially associated with increased brain water, generally in the extra- cellular space.3 MTR(magnetisation Transfer Ratio ).This is reduced when there is pathological change in axonal structure, for example in areas affected by demyelination.
They found that these biomarkers explained a substantial proportion of individual differences in cognitive information-processing speed and general intelligence.The three biomarkers of brain-wide white matter tract integrity explained 10% of the intelligence differences in and even more of the differences in information- processing speed.These factors might be reflecting complementary functional aspects of white matter integrity.
Authors , Penke et al from Edinburgh, concludes that though there might be several heterogeneous neurostructural substrates underlying intelligence, this study provides empirical evidence for one mechanistically plausible neurostructural model of human intelligence differences.
summary of the article:
Penke L, Maniega SM, Bastin ME, Valdés Hernández MC, Murray C, Royle NA, Starr JM, Wardlaw JM, Deary IJ. Mol Psychiatry. 2012 Oct;17(10):1026-30.