Smart means different things to different people. To a scientist it usually means being able to solve hard problems. Measuring this kind of problem-solving intelligence is not difficult. Quite the contrary. In fact, whatever test of intelligence you administer, wether focused on verbal or spatial thinking, the same people tend to do well. This led Psychologist Charles Spearman to propose way back in 1904 that there must be some general factor of intelligence that the tests were measuring. He called it g, and argued that it contributed to success on a wide range of cognitive tasks. g is what I.Q. largely measures (it measures other more specific abilities as well).
Most psychologists did not agree with Spearman, favoring instead the idea that high-level thinking involves many factors. The idea was that analytical thinking requires a large set of separate information handling abilities from different parts of the brain, some spatial, some verbal, many involved with the speed with which particular groups of nerve cells can process information.
Dr. John Duncan of the Medical Research Council in Cambridge, England and colleagues reported in the journal SCIENCE this week that Spearman had it right all along.
Duncan asked people to solve I.Q.-type questions, and while they were attempting to do so, he scanned their brains to see what parts were active. This isn't as bizarre as it sounds. A standard PET (positron emission tomography) brain imaging device measures the relative blood flow in the brain, revealing what parts of the brain are being recruited into action.
The Duncan team tested 60 people ages 29-51 on a range of I.Q. test questions, some testing verbal thinking, others spatial thinking. To screen out all the other extraneous activities going on in an active brain, Duncan administered easy (low-g) and hard (high-g) questions, then looked to see if attempting to solve the hard ones lit up any areas that easy ones did not.
It did. Whenever high-g questions were worked on, the same small region of the brain was activated in each person, just as Spearman's hypothesis predicts. Called the lateral prefrontal cortex, the g region is a zone about the diameter of a golf ball on each side of the brain, above the outer edge of the eyebrow. For spatial problems, people used the g region on both sides of their brain, while for verbal problems they used only the left side.
"What we are seeing here seems to be a global workspace for organizing and coordinating information," Duncan said in an interview with the New York Times. It is the relative performance of this g region workspace -- how it is wired -- that is measured by intelligence tests, he claims.
