UCLA brain mapping researchers have created the first images to show how an individual's genes influence their brain structure and intelligence.
The findings, published in the Nov. 5 issue of the journal Nature Neuroscience, offer exciting new insight about how parents pass on personality traits and cognitive abilities, and how brain diseases run in families.
The team found that the amount of gray matter in the frontal parts of the brain is determined by the genetic make-up of an individual's parents, and strongly correlates with that individual's cognitive ability, as measured by intelligence test scores.
More importantly, these are the first images to uncover how normal genetic differences influence brain structure and intelligence.
Brain regions controlling language and reading skills were virtually identical in identical twins, who share exactly the same genes, while siblings showed only 60 percent of the normal brain differences.
This tight structural similarity in the brains of family members helps explain why brain diseases, including schizophrenia and some types of dementia, run in families.
"We were stunned to see that the amount of gray matter in frontal brain regions was strongly inherited, and also predicted an individual's IQ score," said Paul Thompson, the study's chief investigator and an assistant professor of neurology at the UCLA Laboratory of Neuro Imaging.
"The brain's language areas were also extremely similar in family members. Brain regions that were found to be most similar in family members may be especially vulnerable to diseases that run in families, including some forms of psychosis and dementia."
The scientists employed magnetic resonance imaging technology to scan a group of 20 identical twins, whose genes are identical, and 20 same-sex fraternal twins, who share half their genes.
Using a high-speed supercomputer, they created color-coded images showing which parts of the brain are determined by our genetic make-up, and which are more adaptable to environmental factors, such as learning and stress.
To create the maps of genetic influences on the brain, the UCLA scientists teamed up with the National Public Health Institute of Finland, and the Finnish Universities of Helsinki and Oulu.
In a national initiative, the Finnish team tracked all the same-sex twins born in Finland between 1940 and 1957 -- 9,500 pairs of twins -- many of whom received brain scans and cognitive tests.
Their genetic similarity was confirmed by analyzing 78 different genetic markers. These individual pieces of DNA match exactly in identical twins, and half of them match in siblings.
Recent research has shown that many cognitive skills are surprisingly heritable, with strong genetic influences on verbal and spatial abilities, reaction times, and even some personality qualities, including emotional reactions to stress.
These genetic relationships persist even after statistical adjustments are made for shared family environments, which tend to make members of the same family more similar. Until this study, little was known about how much individual genotype accounts for the wide variations among individual brains, as well as individual's cognitive ability.
The UCLA researchers are also applying this new genetic brain mapping approach to relatives of schizophrenic patients, and individuals at genetic risk for Alzheimer's disease, to screen them for early brain changes, and help understand familial risk for inherited brain disorders where specific risk genes are unknown.
Other UCLA researchers involved in the project are Tyrone Cannon, a professor of psychiatry and biobehavioral and human genetics, and Arthur Toga, professor of neurology and director of the UCLA Laboratory of Neuro Imaging.
Images from the study are available online for viewing or downloading at http://www.