Hemispheric Specialization and Regional Cerebral Blood Flow
Many studies have demonstrated that the two hemispheres are specialized, in the majority of individuals, so that the left hemisphere regulates verbal-analytic cognitive abilities while the right hemisphere predominates in spatial-synthesis functions. The studies also suggested individual differences in the direction and degree of this hemispheric specialization. Thus, not all individuals have the same organization of cognitive processing in the two hemispheres. Our research program has examined these variations both in brain damaged patients and in normals. We have used the tachistoscopic and dichotic listening techniques, as well as paper-and-pencil tests, in the study of left-handed and right-handed males and females. These studies have helped identify reliable behavioural measures of hemispheric functioning. We also made initial steps toward applying the new techniques for measuring regional brain activity to the study of human cognitive functioning. Our studies with the 133-Xenon inhalation technique for measuring regional cerebral blood flow (rCBF) showed lateralized changes in rCBF for verbal and spatial tasks, and the effects were influenced by handedness and sex. We also performed a study of local cerebral glucose metabolism using Positron Emission Tomography (PET), which also found lateralized changes for the standardized cognitive tasks. A second line of research examined hemispheric specialization for emotional processing. Clinical case reports and tachistoscopic studies suggested right hemispheric superiority for emotional processing. Some evidence also suggested hemispheric asymmetry in emotional valence, with the left hemisphere showing a “bias” toward positive affect. These factors are yet to be examined with rCBF.
KeywordsCognitive Activity Regional Cerebral Blood Flow Spatial Task Hemispheric Asymmetry Left Visual Field
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