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<p>The functional status of the frontal cortex in infancy and early childhood is relatively poorly understood, and not much is known about the relationships between the few tasks developed to assess such functioning. The work presented in this thesis investigated these questions using an individual differences approach. Two cohorts of children were tested longitudinally on a set of tasks that have been associated with the frontal cortex in an attempt to establish whether these tasks share common functional mechanisms. Cohort 1 (n = 24) was tested at 9 and 24 months of age, and Cohort 2 (n = 104) was tested at 4 and 9 months of age. Furthermore, a new task, termed the Freeze-Frame task, was developed to assess inhibitory functioning in infancy using eye movements as the dependent measure. The relationship between performance on infant frontal cortex tasks and measures of temperament and general development was also investigated. Finally, a common genetic variation, the COMT Val158Met polymorphism, which has been specifically associated with variation in the neurobiology of the frontal cortex, was investigated in relation to performance on the infant frontal cortex tasks. The results indicated that frontal cortex tasks administered at the same age shared functional mechanisms. Performance indices from the new Freeze-Frame task were associated with performance on several other infant and toddler frontal cortex tasks. Associations between frontal cortex tasks administered at 9 months were stronger than between the tasks administered at 4 months. Longitudinal associations were generally lacking between 4 and 9 months, but some strong associations were found between 9 and 24 months of age. At 4 months of age frontal cortex tasks tended to be associated with better self-regulation as assessed by a parent-report temperament questionnaire. However, at 9 and 24 months of age this pattern had reversed indicating that more reactive children tended to perform better on frontal cortex tasks. Some of the frontal cortex tasks were associated with measures of general cognitive development. However, the associations found between frontal cortex tasks could generally not be accounted for by variation in general cognitive ability. The COMT Val158Met polymorphism was found to be related to a selective aspect of performance on the new Freeze-Frame task, but not to any of the other frontal cortex tasks. The results are discussed in terms of their implications for our understanding of frontal cortex functioning in infancy and early childhood.</p>

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Journal article


Center for Open Science

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