The integration of multiple relations between mental iq,resentations is cri
tical for higher level cognition. For both deductive and inductive-reasonin
g tasks, patients with prefrontal damage exhibited a selective and catastro
phic deficit ii? the integration of relations, whereas patients with anteri
or temporal lobe damage, marched for overall IQ but with intact prefrontal
cortex, exhibited normal relational integration. In contrast, prefrontal pa
tients performed more accurately than temporal patients on tests of both ep
isodic memory and semantic knowledge. These double dissociations suggest th
at integration of relations is a specific source of cognitive complexity fo
r which intact prefrontal cortex is essential. The integration of relations
may be the fundamental common factor linking the diverse abilities that de
pend on prefrontal function, such as planning, problem solving, and fluid i
ntelligence.