Scientists at the University of California - Los Angeles (UCLA) say that a new study lends more force to the suggestion that intelligence is largely inherited.
The researchers used a new type of brain-imaging scanner to show that intelligence is strongly influenced by the quality of the brain's axons, or wiring that sends signals throughout the brain.
Given that the integrity of the brain's wiring is influenced by genes, the researchers suggest that the inheritance of genes play a far greater role in intelligence than was previously thought.
Paul Thompson, a professor of Neurology, points out that genes seem to influence intelligence by determining how well nerve axons are encased in myelin, the fatty sheath of "insulation" that coats the brain’s axons and allows for fast signalling bursts.
The thicker the myelin, says the researcher, the faster the nerve impulses.
During the study, Thompson and his colleagues scanned the brains of 23 sets of identical twins and 23 sets of fraternal twins—considering that identical twins share the same genes while fraternal ones share about half their genes.
The researchers said that they were able to compare each group to show that myelin integrity was determined genetically in many parts of the brain that are key for intelligence—including the parietal lobes, which are responsible for spatial reasoning, visual processing and logic, and the corpus callosum, which pulls together information from both sides of the body.
Thompson highlights the fact that the myelination of brain circuits follows an inverted U-shaped trajectory, peaking in middle age and then slowly beginning to decline.
He believes that identifying the genes that promote high-integrity myelin is critical to forestalling brain diseases like multiple sclerosis and autism, which have been linked to the breakdown of myelin.
"The whole point of this research is to give us insight into brain diseases," he says.
The researcher says that his study has already narrowed down the number of gene candidates that may influence myelin growth, and may one day lead to a therapy that could make people smarter by enhancing their intelligence.
"It's a long way off but within the realm of the possible," Thompson said.
A research article describing Thompson’s study has been published in the Journal of Neuroscience.