A new study conduced by scientists at the California Institute of Technology (Caltech) sheds new light on how the various factors that comprise an "intelligence quotient" (IQ) score depend on particular regions of the brain.

The researchers claim that they have carried out the most comprehensive brain mapping to date of the cognitive abilities measured by the Wechsler Adult Intelligence Scale (WAIS), the most widely used intelligence test in the world

Neuroscientist Ralph Adolphs and postdoctoral scholar Jan Gläscher compiled the maps using detailed magnetic resonance imaging (MRI) and computerized tomography (CT) brain scans of 241 neurological patients recruited from the University of Iowa's extensive brain-lesion registry.

The researchers revealed that all the subjects had some degree of cognitive impairment from events such as strokes, tumour resection, and traumatic brain injury, as assessed by testing using the WAIS.

The WAIS test is composed of four indices of intelligence, each consisting of several subtests, which together produce a full-scale IQ score.

The four indices are the verbal comprehension index, the perceptual organization index that involves visual and spatial processing, the working memory index that represents the ability to hold information temporarily in mind, and the processing speed index.

The researchers first transferred the brain scans of all 241 patients to a common reference frame, an approach pioneered by neuroscientist Hanna Damasio of the University of Southern California, a co-author of the study.