A study has found that the thickness of the insulation of our brain's white matter is directly linked to IQ. Memory, self-control, planning, logic and mathematical ability are all linked to the quality of myelin sheath that protects nervews of white matter from damage. Scientists at the University of California in Los Angeles examined the brains of 23 sets of identical twins and the same number of fraternal twins using a new type of magnetic resonance imaging scanner called HARDI. MRI scans usually show volumes of different tissues in the brain by measuring the amount of water present. HARDI determines water levels diffusing through white matter - an indirect measurement of myelin integrity. The research also found that inherited genes play a greater role in intelligence than was previously thought. Genes appear to affect intelligence by influencing how well nerve fibres are encased in protective and insulating fatty myelin. A good covering of myelin results in faster nerve impulses. "It's like a picture of your mental speed," chief researcher Professor Paul Thompson said. Identical twins share the same genes while fraternal twins share about half their genes. Comparing the results from each showed that myelin integrity was genetically determined in many parts of the brain important for intelligence. They include the corpus callosum, which brings together signals from the left and right side of the body, and the parietal lobes responsible for visual and spatial reasoning and logic. Myelin quality in these areas correlated with scores from tests of abstract reasoning and overall intelligence.
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