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Overall intelligence and localized brain damage

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9/1/07 4:54 PMOverall intelligence and localized brain damagePage 1 of 2http://journals.cambridge.org/action/displayFulltext?type=6&fid=130…30&issueId=02&aid=1305960&fulltextType=RA&fileId=S0140525X07001331closeVolume 30Issue 02 - Apr 2007Cited by Articles(CrossRef)Cited by Articles (GoogleScholar)Citation alertAbstractNext ArticlePrevious ArticlePDF (2.172 MB)Behavioral and Brain Sciences (2007), 30: 173-174 Cambridge University Pressdoi:10.1017/S0140525X07001331Published online by Cambridge University Press 26 Jul 2007Subscribe to journal Email abstract Save citationOpen Peer CommentaryOverall intelligence and localized brain damageDahlia W. Zaidel a1a1 Department of Psychology, University of California–Los Angeles, Los Angeles, CA [email protected] http://dwz.psych.ucla.edu/LabWebSite.htmMedline queryon article authorszaidel dwAbstractOverall mean performance on intelligence tests by brain-damaged patients with focal lesions can be misleading inregard to localization of intelligence. The widely used WAIS has many subtests that together recruit spatially distantneural “centers,” but individually the subtests reveal localized functions. Moreover, there are kinds of intelligence thatdefy the localizationist approach inferred from brain damage.The Parieto-Frontal Integration Theory (P-FIT) of intelligence: Converging neuroimaging evidence Jung Rex E.HaierRichard J. Departments of Neurology and Psychology, University of New Mexico, and The MIND Research Network,Albuquerque, NM 87106 [email protected] www.themindinstitute.org www.positiveneuroscience.com; School ofMedicine, Med Sc I; C237, University of California, Irvine, CA 92697-4475 [email protected]://www.ucihs.uci.edu/pediatrics/faculty/neurology/haier/haier.htmlBrain damage fragments cognition into numerous perceptual and cognitive units that can then be examined with an eyetoward their functional localization in the brain. The 14 subtests of the Wechsler Adult Intelligence Scale (WAIS) arecommonly employed to assess the effects of the damage on different aspects of intelligence. Each subtest relies onseparate or overlapping brain functions, but together all subtests need the computational powers of the entire brain, notjust the frontal-parietal axis. For example, what is required at the very minimum for performing the Information subtestof the WAIS test is intact auditory comprehension, namely Wernicke's Area complex in the left temporal lobe, as well asverbal output, namely Broca's Area complex in the left frontal lobe, together with long-term semantic memory, whichincludes the left hippocampus, the temporal and parietal lobes. To use another example, consider the Block Design, asubtest that measures spatial abilities: The frontal lobes in both the left and right hemispheres are required forforesight, the right parietal lobe for translating the two-dimensional diagrams of the blocks into three-dimensionalconstruction of the blocks, not to mention sustained attention on the task by the left parietal lobe. But what specificbrain regions control performance in the Picture Arrangement subtest (arranging individual pictures so they tell a unifiedstory) besides the occipital lobes, the parietal lobes, commissural fibers, both hemispheres or only one hemisphere, isnot known. All four lobes, in each hemisphere, and possibly subcortical regions, would be expected to contribute tointelligence as measured by the widely employed intelligence tests.In section 7.1, Jung & Haier (J&H) cite studies that did not reveal striking alterations in overall IQ, or intelligence in9/1/07 4:54 PMOverall intelligence and localized brain damagePage 2 of 2http://journals.cambridge.org/action/displayFulltext?type=6&fid=130…30&issueId=02&aid=1305960&fulltextType=RA&fileId=S0140525X07001331back to topgeneral, or just verbal intelligence following localized brain damage, and they use the results as supporting evidence fortheir main thesis. However, such empirical outcomes should not be surprising considering the following: Performance onseveral subtests can compensate for the reduction on only one or two. It is not informative to declare that overallintelligence as measured by the WAIS or a similar test is reduced or not following focal damage. Likewise, with brain-damaged patients, reporting whether or not the Verbal Scale or the Performance Scale of the WAIS is affected, masksthe compensatory contribution of intact regions. What is potentially meaningful in the context of brain lesions is thebreakdown of scores in individual subtests, and, in tests such as the Raven's Progressive Matrices where subtestbreakdown is not possible, the clustering of failed versus successful items, or item analysis results. Finally, the cognitionmeasured by intelligence tests reflects the combined effects of diseased and healthy tissue. The effects of focal andlateralized damage could go against a large regional involvement such as the frontal-parietal axis.Moreover, localized specialized brain regions form pathways and networks connected to each other in selectiveinteractive ways, as J&H point out. However, the extent of their interconnectedness could be critical for optimalperformance on intelligence tests. The issue of high intelligence versus average or low intelligence has not been fullyaddressed in the target article as a function of the interconnectivity. Number of functional axonal fibers and their myelinis a neglected issue in assessing effects of neural injury. Abundant connectivity among widely localized neuronal centerswould be expected for above-average performance on intelligence tests, whereas for average intelligence only limitedconnectivity may be sufficient.Further, there are kinds of intelligence that traditionally have not been subjected to many decades of scrutiny as theWAIS or the Raven's Progressive Matrices (Gardner 1993b; Sternberg 1985). These kinds are complex and cannot bemeasured easily, and consequently brain damage cannot illuminate their components sufficiently to provide clues totheir localization, nor can functional magnetic resonance imaging (fMRI), positron emission tomography (PET), or SinglePhoton Emission Computerized Tomography (SPECT) help here.One need only think of social intelligence, emotional intelligence, athletic intelligence, and artistic intelligence to realizetheir enormous complexity and their unamenability to numerical, analytic measures. There are other types of“intelligences” not


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