New research suggests as much as 10% of individual variances in human intelligence can be predicted based on the strength of neural connections between the left prefrontal cortex and other regions of the brain. WUSTL Image / Michael Cole |
When it comes to intelligence, what factors distinguish the brains of exceptionally smart humans from those of average humans?
As
science has long suspected, overall brain size matters somewhat,
accounting for about 6.7% of individual variation in intelligence. More
recent research has pinpointed the brain’s prefrontal cortex, a region
just behind the forehead, as a critical hub for high-level mental
processing, with activity levels there predicting another 5% of
variation in individual intelligence. Now, new research from Washington
University in St. Louis suggests that another 10% of individual
differences in intelligence can be explained by the strength of neural
pathways connecting the left prefrontal cortex to the rest of the brain.
Published
in the Journal of Neuroscience, the findings establish “global brain
connectivity” as a new approach for understanding human intelligence.
“Our
research shows that connectivity with a particular part of the
prefrontal cortex can predict how intelligent someone is,” suggests lead
author Michael W. Cole, PhD, a postdoctoral research fellow in
cognitive neuroscience at Washington University.
The
study is the first to provide compelling evidence that neural
connections between the left prefrontal cortex and the rest of the brain
make a unique and powerful contribution to the cognitive processing
underlying human intelligence, says Cole, whose research focuses on
discovering the cognitive and neural mechanisms that make human behavior
uniquely flexible and intelligent.
“This
study suggests that part of what it means to be intelligent is having a
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,” says
study co-author Todd Braver, PhD, professor of psychology in Arts &
Sciences and of neuroscience and radiology in the School of Medicine.
Braver is a co-director of the Cognitive Control and Psychopathology Lab
at Washington University, in which the research was conducted.
One
possible explanation of the findings, the research team suggests, is
that the prefrontal region is a “flexible hub” that uses its extensive
brain-wide connectivity to monitor and influence other brain regions in a
goal-directed manner.
“There
is evidence that the left prefrontal cortex is the brain region that
‘remembers’ (maintains) the goals and instructions that help you keep
doing what is needed when you’re working on a task,” Cole says. “So 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.”
While
other regions of the brain make their own special contribution to
cognitive processing, it is the left prefrontal cortex that helps
coordinate these processes and maintain focus on the task at hand, in
much the same way that the conductor of a symphony monitors and tweaks
the real-time performance of an orchestra.
“We’re
suggesting that the left prefrontal cortex functions like a feedback
control system that is used often in engineering, that it helps
implement cognitive control (which supports fluid intelligence), and
that it doesn’t do this alone,” Cole says.
The
findings are based on an analysis of functional magnetic resonance
brain images captured as study participants rested passively and also
when they were engaged in a series of mentally challenging tasks
associated with fluid intelligence, such as indicating whether a
currently displayed image was the same as one displayed three images
ago. Previous findings relating left prefrontal cortex activity to
challenging task performance were supported. 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. Results
indicate that levels of global brain connectivity with a part of left
lateral prefrontal cortex serve as a strong predictor of both fluid
intelligence and cognitive control abilities.
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 augmentatio —of human intelligence. The
findings also may offer new avenues for understanding how breakdowns in
global brain connectivity contribute to the profound cognitive control
deficits seen in schizophrenia and other mental illnesses, Cole
suggests.
