Does a larger brain and skull necessarily imply that a person is more intellectually advanced? The question of where in the brain the intelligence center lies is one that has plagued human intelligence researchers for centuries. Modern technological resources have helped prove that brain size very weakly correlates with intelligence. So how then is intelligence measured and where in the brain is it found?
The primary method for researching intelligence is neuroimaging, a relatively new discipline within medicine and neuroscience that consists of examining brain images. Researcher Richard Haier, a professor of psychology in the School of Medicine at UC Irvine, studied some of the first brain images only 20 years ago. Haier and his partner Rex Jung of the University of New Mexico, have made some influential discoveries in the past couple of years regarding intelligence.
In 2004 Haier and Jung discovered that intelligence is spread throughout various regions of the brain, not collected in any single ‘intelligence center.’ In 2005 they discovered that although women possess more white matter (neuronal connections linking brain centers) and men possess more gray matter (neuronal bodies that process information) there is no significant difference in intelligence levels between genders.
This year, after a review of 37 imaging studies, Haier and Jung have presented a promising hypothesis, the Parieto-Frontal Integration Theory, uncovering evidence of the neural basis of human intelligence.
The Parieto-Frontal Integration Theory identifies regions primarily in the parietal and frontal lobes as those in which individual differences in intelligence can be determined. Although other brain areas are also important to intelligence, the differences therein are minimized to ensure reliability of fundamental functions whereas the P-FIT regions allow differences to flourish without limitations. Furthermore, Haier and Jung point out that most of the areas implicated by the P-FIT are strongly linked to fundamental cognitive processes such as working memory, languages and attention, which suggests that it is the efficiency of the frontal parietal network that determines intelligence levels.
Various brain designs can result in similar intellectual performances; therefore, intelligence is not linked to brain size as much as it is to the effectiveness of information traveling through the brain. The P-FIT model proposes that the temporal and occipital lobes in the frontal area process sensory information which the parietal areas then integrate and abstract, the effectiveness of the interaction between these areas determines intelligence levels. Haier says that their studies identify ‘the stations along the routes that intelligence information takes,’ once the stations are pinpointed they can be studied in relevance to intelligence.
Research consistency has proved that the parieto-frontal network is indeed responsible for defining intelligence. Despite inconsistencies in what brain intelligence consists of, how it is measured and how it is defined, Haier and Jung found consistency in their imaging analysis even while using a variety of measuring methods. Although small inconsistencies and conflicts still remain to be resolved, genetic research has suggested that intelligence possibly can be inherited. Therefore, according to Haier, ‘genes work through biology, there must be a biological basis for intelligence.’
Neuroimaging studies are currently in a promising stage and the P-FIT highlights these advances in determining the biological basis for intelligence. The P-FIT is nevertheless merely the framework for further research. As Haier pointed out, targeting the areas of the brain that house intelligence will eventually help treat problems such as mental retardation whose roots lie in low levels of intelligence.
In a field where data is mountainous but theories weak, the P-FIT is a welcomed hypothesis that is only the beginning. With a world class Brain Imaging Center (BIC) offering a state of the art High Resolution Research Tomograph (HRRT) that is one of only 13 in the world and five in the United States, along with dedicated professors such as Richard Haier, UCI’s potential is limitless as it maintains its position at the forefront of brain imaging research.