A new study suggests that the strength of neural pathways in the prefrontal cortex is a factor in increased intelligence.
Researchers from Washington University in St. Louis say this “global brain connectivity” explains about 10 percent of the variance in individual intelligence.
Previous studies have shown that brain size matters, accounting for about 6.7 percent of individual variation in intelligence, the researchers note.
More recent research has pinpointed the brain’s lateral prefrontal cortex, a region just behind the temple, as critical for high-level mental processing, with activity levels there predicting another 5 percent of variation in individual intelligence.
This new research suggests that another 10 percent of individual differences in intelligence can be explained by the strength of neural pathways connecting the left lateral prefrontal cortex to the rest of the brain.
The findings establish “global brain connectivity” as a new approach for understanding human intelligence, according to lead author Michael W. Cole, Ph.D., a postdoctoral research fellow in cognitive neuroscience at Washington University.
“This study suggests that part of what it means to be intelligent is having a lateral prefrontal cortex that does its job well; and part of what that means is that it can effectively communicate with the rest of the brain,” said study co-author Todd Braver, Ph.D., professor of psychology.
According to the research team, one possible explanation for the findings is that the lateral prefrontal region is a “flexible hub” that uses its extensive brain-wide connectivity to monitor and influence other regions in the brain in a “goal-directed manner.”
The researchers explain that there is evidence that the lateral prefrontal cortex is the region in the brain that “remembers” the goals and instructions that help you keep doing what is needed when you’re working on a task.
“It makes sense that having this region communicating effectively with other regions — the ‘perceivers’ and ‘doers’ of the brain — would help you to accomplish tasks intelligently,” Cole said.
The research team compares the lateral prefrontal cortex to a symphony conductor, who monitors and tweaks the real-time performance of an orchestra.
“We’re suggesting that the lateral prefrontal cortex functions like a feedback control system,” Cole said, adding that “it helps implement cognitive control, which supports fluid intelligence, and that it doesn’t do this alone.”
The findings are based on an analysis of functional magnetic resonance brain images captured as study participants rested and also when they were engaged in a series of mentally challenging tasks, such as indicating whether an image was the same as one displayed three images ago.
Previous findings relating lateral prefrontal cortex activity to challenging task performance were supported, the researchers said. Connectivity was then assessed while participants rested, and their performance on additional tests of fluid intelligence and cognitive control collected outside the brain scanner was associated with the estimated connectivity, they said.
Although much remains to be learned about how these neural connections contribute to fluid intelligence, new models of brain function suggested by this research could have important implications for the future understanding — and perhaps augmentation — of human intelligence, according to the researchers.
The findings also may offer new avenues for understanding how breakdowns in global brain connectivity contribute to the cognitive control deficits seen in schizophrenia and other mental illnesses, Cole hypothesized.
The new research is published in the Journal of Neuroscience.