Measuring human intelligence may be controversial and oh-so-verytricky to do. A new study, however, demonstrates 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 behaviour that is exceptionally flexible, responsive and capable of navigating complexity requires something beyond a strong and active prefrontal corte 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 per cent 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 seven per cent 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 latest study underscores a growing appreciation among neuroscientists for the importance of the brain's "white matter" - fatcovered clusters of axons that string neurons and the brain's two hemispheres together - in brain function. Our volume of "grey matter" is popularly spoken of as a measure of intelligence. But research increasingly shows that when the "white matter" that ties the grey 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.
