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IQ tests have been around for more than a century. They were originally created in France to help identify students who needed extra help in school.
The U.S. government later used modified versions of these tests during World War I. Leaders in the armed forces knew that letting unqualified people into battle could be dangerous. So they used the tests to help find qualified candidates. The military continues to do that today. The Armed Forces Qualification Test is one of many different IQ tests in use.
IQ tests have many different purposes, notes Joel Schneider. He is a psychologist at Illinois State University in Normal. Some IQ tests have been designed to assess children at specific ages. Some are for adults. And some have been designed for people with particular disabilities.
But any of these tests will tend to work well only for people who share a similar cultural or social upbringing. “In the United States,” for instance, “a person who has no idea who George Washington was probably has lower-than-average intelligence,” Schneider says. “In Japan, not knowing who Washington was reveals very little about the person’s intelligence.”
Questions about important historical figures fall into the “knowledge” category of IQ tests. Knowledge-based questions test what a person knows about the world. For example, they might ask whether people know why it’s important to wash their hands before they eat.
IQ tests also ask harder questions to measure someone’s knowledge. What is abstract art? What does it mean to default on a loan? What is the difference between weather and climate? These types of questions test whether someone knows about things that are valued in their culture, Schneider explains.
Such knowledge-based questions measure what scientists call crystallized intelligence. But some categories of IQ tests don’t deal with knowledge at all.
Some deal with memory. Others measure what’s called fluid intelligence. That’s a person’s ability to use logic and reason to solve a problem. For example, test-takers might have to figure out what a shape would look like if it were rotated. Fluid intelligence is behind “aha” moments — times when you suddenly connect the dots to see the bigger picture.
Aki Nikolaidis is a neuroscientist, someone who studies structures in the brain. He works at the University of Illinois at Urbana-Champaign. And he wanted to know what parts of the brain are active during those “aha” episodes.
In a study published earlier this year, he and his team studied 71 adults. The researchers tested the volunteers’ fluid intelligence with a standard IQ test that had been designed for adults. At the same time, they mapped out which areas of test takers’ brains were working hardest. They did this using a brain scan called magnetic resonance spectroscopy, or MRS. It uses magnets to hunt for particular molecules of interest in the brain.
As brain cells work, they gobble up glucose, a simple sugar, and spit out the leftovers. MRS scans let researchers spy those leftovers. That told them which specific areas of people’s brains were working hard and breaking down more glucose.
People who scored higher on fluid intelligence tended to have more glucose leftovers in certain parts of their brains. These areas are on the left side of the brain and toward the front. They’re involved with planning movements, with spatial visualization and with reasoning. All are key aspects of problem solving.
“It’s important to understand how intelligence is related to brain structure and function,” says Nikolaidis. That, he adds, could help scientists develop better ways to boost fluid intelligence.