Research has shown that people with more grey matter score high on cognitive tests. A new study found the gene that links the thickness of grey matter with intelligence.

The study, conducted by researchers at King's College London and colleagues, could help understand why some people have learning disabilities.

Scientists have been trying for years to find the root of intelligence. The prefrontal lobe- the part of brain right behind the forehead- was earlier thought to be associated with intelligence. However, recent research in neuroscience is now pointing towards the outermost layer of the brain- the cerebral cortex or grey matter- as the site for intelligence.

Other researchers found a link between thickness of this region and intelligence. The present study went a step ahead and found a gene variant that was responsible for this link.

Data for the study came from children enrolled in the IMAGEN cohort. Researchers collected DNA samples and looked at brain scans of 1,583 healthy 14-year-old teenagers. Study participants also underwent several cognitive tests.

"We wanted to find out how structural differences in the brain relate to differences in intellectual ability. The genetic variation we identified is linked to synaptic plasticity - how neurons communicate. This may help us understand what happens at a neuronal level in certain forms of intellectual impairments, where the ability of the neurons to communicate effectively is somehow compromised," Dr Sylvane Desrivières, from King's College London's Institute of Psychiatry and lead author of the study, said.

Note that the gene accounts for about 0.5 percent of the variation in intelligence, meaning that there are several other factors that might explain why some people are smarter than others.

"It's important to point out that intelligence is influenced by many genetic and environmental factors. The gene we identified only explains a tiny proportion of the differences in intellectual ability, so it's by no means a 'gene for intelligence'," Desrivières said in a news release.

Researchers looked at some 54,000 genetic variants that are known to be involved in brain development. They found that teenagers that carried one gene variant were more likely to have a thinner cortex in left part of the brain. These adolescents even performed poorly on various cognitive tests.

This particular variant in NPTN gene is associated with building neuronal synapses. In other words, the gene variant doesn't let different parts of the brain "talk" and synchronize tasks, leading to poorer cognitive performance.

Researchers also used a mouse model to study the effects of the NTPN gene in brain activity. They found that the left hemisphere of the brain was more likely to be affected by the variant than the right hemisphere.

The study might help researchers understand the mechanism associated with brain disorders such as autism and schizophrenia.

The study is published in the journal Molecular Psychiatry.