Doctor of Philosophy
Dr. Elizabeth Hampson
Sex hormones are important factors in the establishment of sex differences in the brain and behaviour during the prenatal developmental period and during adulthood. One brain area that has received little attention with respect to the study of sex differences is the prefrontal cortex (PFC). The PFC is involved in cognitive functions not limited to working memory, reinforcement learning, and inhibitory control. Currently, our understanding of the hormonal modulation of the PFC by sex steroids is also limited. The overall objectives of the present thesis were: to test the hypothesis that select cognitive functions known to depend on the PFC exhibit sex differences, to investigate whether some of these functions are influenced by developmental and/or adult androgens, and to begin to determine the functional components of PFC-dependent cognitive tasks that are responsible for eliciting sex differences. In Study 1, there was no evidence for a sex difference on two working memory tasks (Self-Ordered Pointing and the n-back), but males selected more advantageous cards than females on the Iowa Gambling Task (IGT) and were more accurate during the reversal phase of a probabilistic reversal learning task. In Study 2, the relationship between current and developmental androgens and performance on the IGT was investigated. Financial risk-taking was assessed as a potential mediator of the relationships. Circulating testosterone was found to be negatively correlated with the number of good card selections on the IGT, but there was no evidence to suggest that risk-taking was a mediator. On the other hand, there was evidence that developmental levels of androgens (using digit ratio as a proxy measure) may influence IGT performance in adulthood indirectly through an effect on risk-taking. In Study 3, females were more accurate than males on a reinforcement learning task under conditions where learning was based on positive feedback, whereas males were faster on an interference inhibition task than females. Taken together, the set of studies described in the present dissertation advance our knowledge regarding the sexual differentiation of the PFC and add to our current understanding of the modulatory role played by sex steroids on certain cognitive functions dependent on the PFC.
Evans, Kelly L., "Sexual Differentiation of the Prefrontal Cortex in Humans: Examining Behavioural Sex Differences and the Modulatory Role of Androgens" (2013). Electronic Thesis and Dissertation Repository. 1938.