Sexual differentiation of working memory in humans

by Duff Canning, Sarah Jane

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 ncurophysiological and behavioral data that suggest that estrogens may modulate the îctivity of the adult primate prefrontal cortex (PFC). in humans. the PFC mediates a number o C cognitive processes that contribute to memory Function. particularly working memory. Recent studies have suggested that the dorsolateral PFC (DLPFC) is essential for the cxecutive processes that contnbute to working mernory. including the active manipulation and transformation of information in rnernory. Because the DLPFC is among the areas for which there is evidcnce of estrogen sensitivity. these findings raise the possibility that the working memory processes dependent on this region may be wsciiptible to the activational effccts of estrogens and consequently may exhibit evidcnce of sesual di ffcrentiation. Thc tirst study of the present thesis investigated the possibility that a sa diffcrcnce might exist in PFC-dependent working memory processes in hcalthy human adults. In thrcc separate experiments. healthy male and female undergraduates were adininistcrcd a novel spatial working rnemory task and. in Experiment 3. a verbal working rncmory task that had previously been show in neuroimaging studies to reliably activate the DLPFC. Both tasks emphasized the active manipulation of information in short-tcrm memory and therefore were assumed to recruit PFC-Jependent working mcmory processes. In three experiments. females were found to commit significantly fcwcr working mrmory errors and took significantly iess time to reach criterion than malcs on the Spatial Working Memory task (SPWM). Control tasks revealed that the fcmalc advantage was not accounted for by group differences in generai intellectual ability. irnmediate span of attention. perceptual speed. incidental mernory. speed of verbal access, or other extraneous firnctions. A similar ses difference was observed on the verbal working memory measure. These tindings were consistent with the hypothesis that working mernory processes mediated by the DLPFC might be sexually differentiated. The second study directly investigated the hypothesis that the working rnernory system was sensitive to estrogen in adult humans. Specifically. this study examineci whether rnemory tasks that involve an active manipulative component rnight exhibit cstrogen sensitivity in women. Performance on several memory tasks, including rncasures of working rnemory, was evaluated in postmenopausal women taking estrogen alonc. estrogen and progestin concurrently, and in women not receiving hormone rcplûcement therapy. Estrogen users performed significantly better than non-uscrs on a verbal tnsk and on a spatial task. which placed heavy demands on the ability to actively mnnipulate infonation in memory. In contrûst. no group differences were detected on control rneasurcs that simply involved passive recall of information. These findings supportcd thc hypothesis that circulating estrogens are capable of intlüencing working rnemory functions believçd to depend on the DLPFC. Considercd together. the results frorn these hvo studies support the possibility that csccutive processcs that depend on the PFC and that contribute to working memory might bc sexually differentiated in humans.