Mapping Intelligence to the Brain
Intelligence. We understand the concept, and the meaning of this word, but where in the brain, precisely, is intelligence actually located? Until recently, we did not really, have a clue. Now, using perhaps the most common sense approach possible, from neuroscientists at the California Institute of Technology have mapped the cognitive zones of the human brain.
The researchers have constructed a 3D model of precisely where intelligence and other cognitive powers reside, within the human brain, by making use of the WAIS test.
The WAIS or Wechsler Adult Intelligence Scale test is composed of four indices of intelligence, each consisting of several sub-tests, 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 organisation 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.
For research subjects, both MRI and CT scans of each of of 241 neurological patients recruited from the University of Iowa's extensive brain-lesion registry were compared. Each of the patients had some degree of cognitive impairment from events such as strokes, tumour resection, and traumatic brain injury.
The researchers first transferred the brain scans of all 241 patients to a common reference frame, using volumetric modelling. Then they mapped the brains, using a technique called voxel-based symptom-lesion mapping, with a resolution of one voxel (3D pixel) per cubic millimetre. This gave relatively precise 3D structures for each patient, that showed the areas of brain damage, and severity of damage in a format that could be directly overlaid and compared with other samples.
By then comparing the type of brain impairment from WAIS test results, across each of the 241 patients, and noting the areas of overlap in damage when there were similar cognitive defecits, the researchers have been able to painstakingly map out an accurate and relatively verifiable map of the areas of the brain responsible for each element of intelligence.
That means that the 3D map produced, can be overlaid directly onto medical CT / MRI data, once converted, and allow doctors to pinpoint exactly what aort of effects to expect in a person's mental faculties following brain damage. The converse - using brain-scan results to predict the IQ of patients as measured by the Weschler test - may also be possible.
Examples of the type of data produced include:
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 organisation 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.