Intelligence genes theory backed
Updated on 11 March 2009
Inherited genes play a far greater role in intelligence than was previously thought, new research suggests.
A new type of scanner has shown the quality of brain wiring is largely heritable and linked to IQ.
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.
Other inherited features in the brain were already known to have an impact on IQ.
One was the volume of grey matter, the brain's "processor" cells. The other was the amount of "white matter" nerve fibres connecting the processor neurons.
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.
"It's like a picture of your mental speed," chief researcher Professor Paul Thompson told New Scientist magazine.
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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