Variations in Functional Lateralization

Sammanfattning: The general aim of this thesis was to study asymmetric activation of the neocortex in normal subjects, using the rCBF technique and different cognitive tasks. The aim was also to study individual and group variations of asymmetric activation, as well as factors pertaining to these variations. The thesis is based on four investigations. In the first investigation different visuo-spatial tasks were used. The most important finding was that cube analysis caused an asymmetry to the right in the posterior association cortex (PTO-cortex), and that this asymmetry was positively correlated to performance on the task ­ the larger the magnitude of asymmetry to the right, the higher was the score on cube analysis. Two studies of ethanol effects were accomplished, one during reversing checkerboard stimulation, the other during verbal fluency. Together they showed that following ethanol the normal rCBF distribution at rest, with its typical hyperfrontality was preserved, and that hemispheric means of CBF increased during both rest and activation. Further, the rCBF activation response indicates the preserved coupling between regional neuronal activity and rCBF during ethanol inebriation. Together they show that ethanol can be used as a means to experimentally induce transient changes in the functional systems of the brain, and that changes in brain functions can be studied by rCBF techniques also during ethanol inebriation. The second study reveals that ethanol changes the brain´s response to visual stimulation, causing the asymmetries found in the sober state to disappear. The third study showed that the frontotemporal region had a preserved activation response following ethanol. This indicates that the component of the active network that produces motor programs for speech is more robust to the detrimental effects of ethanol inebriation than other parts of it. In the rest of the left DLPFC the activation response was absent following ethanol, indicating a less differentiated cortical information processing. It might represent a disturbance in one or some working memory, and/or temporal memory, and/or short-term memory functions. The inferiority of processing information by bilateral activation was further suggested in the third study by a decrease in the number of words produced during inebriation. Ethanol seems to have detrimental effects on cortical flow asymmetries both frontally and posteriorly, and in both hemispheres. In the fourth study a highly creative and a low creative group was compared during rest and three tasks, ending with a divergent task (uses of objects). The main finding was that when performing uses of objects compared to verbal fluency, the highly creative group had bilateral anterior prefrontal increases, while the low creative group used functions predominantly on the left side in the frontotemporal region. This indicates a return to bilaterality when more complex, such as creative, functions are addressed e.g. by divergent tasks.