(MCT)—Measuring human intelligence may be controversial and oh-so-very-tricky to do. But like obscenity, we think we know it when we see it. A new study, however, demonstrates a more rigorous way to see and measure differences in intelligence between individuals. It finds that connectedness among the brain’s disparate regions is a key factor that separates the plodding from the penetrating.
As many researchers have long suspected, intelligence does have a “seat” in the human brain: an area just behind each of the temples called the lateral prefrontal cortex. But researchers writing in the journal Neuroscience found that human behavior that is exceptionally flexible, responsive and capable of navigating complexity requires something beyond a strong and active prefrontal cortex: strong and agile runners must link that seat to brain regions involved in perception, memory, language and mobility.
The researchers estimate that the strength of those connections, as measured when subjects rested between mental tasks, explains about 10 percent of differences in intelligence among individuals. That makes this measure an even better predictor of intelligence than brain size — a measure that scientists believe may explain about 7 percent of the variation in intelligence among individuals.
To detect this relationship, the Neuroscience study compared functional magnetic resonance imaging (fMRI) brain scans of 78 men and women between 18 and 40 years old with those subjects’ performance on tests of cognitive performance that required “fluid intelligence” and “cognitive control.” Subjects, for instance, were asked to count backwards by, say, nine, or to watch a series of visual images and then indicate whether a single image shown had been among them.
The resulting picture of intelligence is a remarkably simple one: from a single hub in the prefrontal lobes radiates a plethora of brightly lit connections to all corners of the brain. This suggests that when we engage in goal-directed behavior that requires judgment, sustained attention and flexibility, the two sides of the prefrontal lobe coordinate incoming information, send out commands and keep us on task, said the study’s lead author, Michael W. Cole of Washington University’s cognitive neuroscience department.
To do all that well, it needs to maintain connections throughout the brain that have speed and high capacity.
The latest study underscores a growing appreciation among neuroscientists for the importance of the brain’s “white matter” — fat-covered clusters of axons that string neurons and the brain’s two hemispheres together — in brain function. Our volume of “gray matter” is popularly spoken of as a measure of intelligence. But research increasingly shows that when the “white matter” that ties the gray stuff together is damaged or deficient — as it can be in patients with brain trauma, autism and schizophrenia — goal-directed task performance can be very poor.
©2012 Los Angeles Times
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