The study, published in the Journal of Neuroscience, looked at the brains and intelligence of 92 people. All the participants took standard IQ tests. Then the researchers studied their brains using a technique called diffusion tensor imaging, or DTI.
Capturing Mental Speed
DTI is a variant of magnetic resonance imaging (MRI) that can measure the structural integrity of the brain's white matter, which is made up of cells that carry nerve impulses from one part of the brain to another. The greater the structural integrity, the faster nerve impulses travel.
"These images really give you a picture of the mental speed of the brain," says Paul Thompson, Ph.D., a professor of neurology at UCLA School of Medicine.
They're also "the most beautiful images of the brain you could imagine," Thompson says. "My daughter, who's 5, says they look like little flowers at each point in the brain."
Thompson says DTI scans of the 92 participants in the study revealed a clear link between brain speed and intelligence.
"When you say someone is quick-thinking, it's genuinely true," Thompson says. "The impulses are going faster and they are just more efficient at processing information, and then making a decision based on it."
Thompson's study also found that genetic factors played a big role in brain speed.
The team was able to figure this out because the 92 people in their study were all twins. Some were identical twins, who share all the same genes. Others were non-identical twins, who share only certain genes.
By comparing the groups, the researchers were able to tease out genes associated with the structural integrity of white matter. And it turned out many of these genes were also associated with intelligence.
Richard Haier, Ph.D., emeritus professor at the University of California, Irvine, says this may explain something scientists have been wondering about for a long time.
"We know that intelligence has some genetic component," he says. "And what the Thompson study is showing is that a large part of the genetic aspect of intelligence has to do with the white matter tracks that connect different parts of the brain."
Don't Give Up Just Yet
Haier says the good news is that we're not necessarily stuck with the brain, or the brain speed, we inherit. He says thinking is like running or weightlifting. It helps to have certain genes. But anyone can get stronger or faster by working out.
The brain is like a muscle, Haier says: "The more you work it the more efficient it gets."
So people who practice the violin, or do math problems, or learn a foreign language are constantly strengthening certain pathways in their brains.
And Thompson notes that our brains, unlike our bodies, peak relatively late in life.
"The wires between the brain cells, the connections, are the things that you can modify throughout life," he says. "They change and they improve through your 40s and 50s and 60s."
Thompson says there are practical, as well as academic, reasons to measure brain speed.
The technique can spot problems such as Alzheimer's disease, which slows down the brain. And because the scans are so sensitive, they can show whether new drugs for Alzheimer's are actually working.