“...we decided to carry out a rather large scale brain-imaging study to enable us to examine both cognitive individual differences and those relating to affective differences as well”

In general, cognitive neuroscientists are beginning to become quite interested in individual differences. Human intelligence—in the sense of reasoning and problem-solving ability, or fluid intelligence—is a major dimension of individual differences, and the neurobiological mechanisms are not only intriguing but also currently poorly understood. Our study also contained several methodological advances over previous work.

The paper was the first to use the variability of fluid intelligence within a large sample of individuals (48) to identify brain regions that might support fluid intelligence, namely the lateral prefrontal and lateral parietal cortex. Our study went beyond identifying which areas are important, by indicating the specific cognitive conditions in which these areas seem to be most critical. These conditions appear to be ones where information has to be kept actively in mind and also protected against sources of interference. Previous neuroimaging studies had either used small samples, or had compared harder against easier tasks. In addition, we used multivariate methods (specifically, path analysis) to formally test whether specific brain regions could mediate the relation between higher intelligence and better task performance.

We found that individual differences in fluid intelligence (or reasoning and novel problem-solving ability) are mediated by brain areas that help control attention. Individual differences matter greatly in everyday life, including education, employment, and health. Cognitive neuroscientists are increasingly interested in the brain bases of individual differences, and in particular the challenges and rewards of studying why and how individuals vary in thinking-style and ability.