Caltech neuroscientists analyzed MRI and CT scans of brains of 241 patients from the University of Iowa’s registry of brain lesions. By correlating different types of cognitive ability with injuries in the organ, they were able to build a 3D intelligence map of the brain.
All of the patients had some degree of cognitive impairment from events such as strokes, tumor 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, 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 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 coauthor of the study. Using a technique called voxel-based symptom-lesion mapping (a voxel is the three-dimensional analog of a pixel, and represents a volume of about 1 cubic millimeter), Adolphs and his colleagues then correlated the location of brain injuries with scores on each of the four WAIS indices.
“The first question we asked was if there are any parts of the brain that are critically important for these indices or if they are very distributed, with intelligence processed globally in a way that can’t be mapped,” Adolphs [Caltech neuroscientist Ralph Adolphs] says. 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.
Press release: Mapping Intelligence in the Brain…