Fluid intelligence and executive functions: New perspectives.

Spearman (1904) introduced the concept of generaI intel1igence (g) to describe the universal positive correlation among tests of different abilities. He later defined g as a "mental energy" that could be applied to any and every kind of task (Spearman, 1927). What g is and which role it plays in cognitive processing is stil1 under debate (Jensen, 1998). From a psychometric point of view g is the result of two main factors called gc (crystallized intelligcncc) and gf (fluid intclligence) that reflect the amount of knowledge and the ability to educe relations, respectively. Recently a large number of studies focused their attention on the biological basis of g and its relationship with other cognitivc functions. The leading idea is that g could be strongly linked to the executive control system (Deary, 2000). This idea is supported by some behavioural, lesions and bioimaging studies. The activation of the lateral prefrontal cortex during fluid reasoning tasks (Duncan, Seitz, Kolodny, Bor, Herzog, Abmed, Newell, and Emslie, 2000) and the involvement of a domain-independent working memory system in problem solving, localized in the prefrontal areas (Prabakaram, Smith, Desmond, Glover, and Gabrieli, 1997), give a great contribution to the supposed link between g and some frontal lobe functions. The data obtained on frontal patients seem to go in the same direction: the dysexecutive syndrome caused by lesions in the lateral prefrontal cortex is often associated with a dec1ine in fluid reasoning (Duncan, Burgess, and Emslie, 1995). On normal subjects, some authors find a significant correlation between executive abi1ities and performances in gf tests (Duncan, Emslie, Williams, Johnson, and Freer, 1996). All these data will be largely reviewed and integrated in a unique framework.