GENES play a far greater role in intelligence than was previously thought, new research suggests.
A new type of scanner has shown that 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
results in faster nerve impulses.
Other inherited features in the brain were already known to have an impact on IQ. One is the volume of grey matter, the brain's "processor" cells. The other is the amount of "white matter", nerve fibres connecting the processor neurons.
Scientists at the University of California in the United States 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," Professor Paul Thompson, the chief researcher, 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.
There might be a way to identify the genes involved and enhance their activity, Prof Thompson said.
This in turn could lead to treatments for multiple sclerosis, autism and attention deficit disorder, which are all associated with lack of myelin.
