Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Gonadal hormones appear to modulate many aspects of behavior in non-human species. In this thesis, a series of studies was undertaken to determine whether the variations in estrogen and progesterone levels that occur naturally over the menstrual cycle are sufficient to affect cognitive and motor functioning in humans. It was predicted that: (1) Variations in sexually dimorphic skills would be evident over the menstrual cycle; and that (2) High levels of estrogen and progesterone would be associated with better performance on tests at which women typically excel, but poorer performance on tests at which men typically excel, relative to performance when steroid levels are low.;The first study provided preliminary support for these hypotheses. At the midluteal phase of the cycle, characterized by high levels of estradiol and progesterone, a group of normally-cycling young women showed improved performance on several tests of speeded manual coordination, relative to their performance during menses, when levels of these hormones are low. In contrast, they displayed poorer performance at the midluteal phase on a test of perceptuo-spatial skill, known to favor males.;A second study investigated the generalizability of these findings. The midluteal phase was found to be associated with enhanced performance on tests of verbal fluency, articulation and fine motor skills. In contrast, women at the menstrual phase performed better on tests of spatial ability and deductive reasoning.;In a final study, women were tested during menstruation and during the preovulatory surge in estradiol, to determine whether high levels of estradiol alone are sufficient to account for these effects. High levels of estradiol were associated with better performance on tests of articulation and fine motor skills, but poorer performance on tests of spatial ability. A curvilinear relationship between serum estradiol level and performance was noted for one of the three spatial tests.;Results support the view that gonadal steroids may exert a small but significant effect on human brain activity, and thence, behavior. Activational effects of gonadal steroids may contribute in part to sex differences in cognitive and motor functions.



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