There's certainly more than one way to be intelligent, since Al Capone was street smart, Emily Dickinson book smart, and Bill Clinton people smart. Now, however, a team of neuroscientists claims to have pinpointed a site for "general intelligence" in the frontal cortex of the brain. Skeptics retort that the new study doesn't make the case for a single, multipurpose intelligence center.
The dispute over the nature of intelligence stretches back nearly 100 years to observations by Charles Spearman, a British army officer and statistics maven who noticed that people who score high on one kind of cognitive test also tend to perform well on other types of mental tests. To Spearman, the correlation implied that intelligence was a single quality, which he dubbed general intelligence, or g. Spearman's critics argued that intelligence was multifaceted, dismissing g as a statistical artifact or the consequence of a narrow set of test questions. A century of statistical analysis, cognitive tests, and bickering haven't settled the debate.
Trying a different approach, neuroscientist John Duncan of the Medical Research Council in Cambridge, United Kingdom, and colleagues examined brain activation in people solving problems that require different kinds of skills, such as verbal abilities and spatial abilities. If each cognitive task calls on its own seat of intelligence, different brain regions should activate depending on the task. To test this idea, the researchers trained a positron emission tomography (PET) scanner on 13 subjects as they worked on verbal and spatial problems that varied in difficulty.
When the subjects mulled the more challenging, "high-g" questions, an area in the frontal cortex just above the temple lit up in the PET scan--regardless of whether the questions targeted spatial or verbal reasoning. But when they attempted the easier, "low-g" questions, the same area remained dark, the researchers report in the July 21 issue of Science. That the same small area of the brain revved up during quite different tasks argues for a single, multipurpose analytical "module" that helps solve many problems, Duncan says.
Critics aren't buying it. Though the questions would seem to require spatial and verbal skills, both are essentially visual tasks, says psychologist John Moore of the University of Massachusetts, Amherst. The elevated activity in the frontal region may reflect extra visual processing--a mental activity that isn't the same thing as what we think of as intelligence, he says.