Neuroscientists at Caltech have conducted the most comprehensive brain mapping to date of the cognitive abilities measured by the Wechsler Adult Intelligence Scale, the most widely used intelligence test in the world. Will this change the entire way we think about IQ?

Yes. The results of the study which will appear in the form of a paper, "Lesion Mapping of Cognitive Abilities Linked to Intelligence," in the March 12 issue of Neuron, offer new insight into how the various factors that comprise an "intelligence quotient" (IQ) score depend on particular regions of the brain.

Caltech Neuroscientists scanned of 241 neurological patients recruited from the University of Iowa's extensive brain-lesion registry to study four indices—the verbal comprehension index, which represents the ability to understand and to produce speech and use language; the perceptual organization index, which involves visual and spatial processing, such as the ability to perceive complex figures; the working memory index, which represents the ability to hold information temporarily in mind (similar to short-term memory); and the processing speed index.

The results indicated that, with the exception of processing speed, which appears scattered throughout the brain, the lesion mapping showed that the other three cognitive indices really do depend on specific brain regions. For example, lesions in the left frontal cortex were associated with lower scores on the verbal comprehension index; lesions in the left frontal and parietal cortex (located behind the frontal lobe) were associated with lower scores on the working memory index; and lesions in the right parietal cortex were associated with lower scores on the perceptual organization index.

Somewhat surprisingly, the study revealed a large amount of overlap in the brain regions responsible for verbal comprehension and working memory, which suggests that these two now-separate measures of cognitive ability may actually represent the same type of intelligence, at least as assessed using the WAIS, according to Caltech.

The impact is substantial: This research could lead to future revisions of the WAIS test so that its various subtests are grouped on the basis of neuroanatomical similarity rather than on behavior, as is the case now. In addition, the brain maps could help clinicians combine the maps with their patients' Wechsler test results to help localize likely areas of brain damage. Third, using brain-scan results to predict the IQ of patients as measured by the Weschler test may also be possible. Is IQ a completely accurate way of measuring intelligence anyway? Tell us what you think.