| The present thesis investigated the possibility that the working memory system might be sexually differentiated in adult humans. Of central importance to this thesis are neurophysiological and behavioral data that suggest that estrogens may modulate the activity of the adult primate prefrontal cortex (PFC). In humans, the PFC mediates a number of cognitive processes that contribute to memory function, particularly working memory. Recent studies have suggested that the dorsolateral PFC (DLPFC) is essential for the executive processes that contribute to working memory, including the active manipulation and transformation of information in memory. Because the DLPFC is among the areas for which there is evidence of estrogen sensitivity, these findings raise the possibility that the working memory processes dependent on this region may be susceptible to the activational effects of estrogens and consequently may exhibit evidence of sexual differentiation.;The first study of the present thesis investigated the possibility that a sex difference might exist in PFC-dependent working memory processes in healthy human adults. In three separate experiments, healthy male and female undergraduates were administered a novel spatial working memory task and, in Experiment 3, a verbal working memory task that had previously been shown in neuroimaging studies to reliably activate the DLPFC. Both tasks emphasized the active manipulation of information in short-term memory and therefore were assumed to recruit PFC-dependent working memory processes. In three experiments, females were found to commit significantly fewer working memory errors and took significantly less time to reach criterion than males on the Spatial Working Memory task (SPWM). Control tasks revealed that the female advantage was not accounted for by group differences in general intellectual ability, immediate span of attention, perceptual speed, incidental memory, speed of verbal access, or other extraneous functions. A similar sex difference was observed on the verbal working memory measure. These findings were consistent with the hypothesis that working memory processes mediated by the DLPFC might be sexually differentiated.;The second study directly investigated the hypothesis that the working memory system was sensitive to estrogen in adult humans. Specifically, this study examined whether memory tasks that involve an active manipulative component might exhibit estrogen sensitivity in women. Performance on several memory tasks, including measures of working memory, was evaluated in postmenopausal women taking estrogen alone, estrogen and progestin concurrently, and in women not receiving hormone replacement therapy. Estrogen users performed significantly better than non-users on a verbal task and on a spatial task, which placed heavy demands on the ability to actively manipulate information in memory. In contrast, no group differences were detected on control measures that simply involved passive recall of information. These findings supported the hypothesis that circulating estrogens are capable of influencing working memory functions believed to depend on the DLPFC.;Considered together, the results from these two studies support the possibility that executive processes that depend on the PFC and that contribute to working memory might be sexually differentiated in humans. |
