Implicit memory varies across the menstrual cycle: estrogen effects in young women.

Evidence that ovarian steroid hormones such as estrogen and progesterone affect cognition comes from studies of memory in older women receiving estrogen replacement therapy and studies of sexually dimorphic skills in young women across the menstrual cycle. Sixteen women (ages 18-28) completed tests of memory (implicit category exemplar generation, category-cued recall, implicit fragmented object identification) and sexually dimorphic skills (fine motor coordination, verbal fluency, mental rotations) at the early follicular (low estrogen and progesterone) and midluteal (high estrogen and progesterone) phases of the menstrual cycle. Performance on category exemplar generation, a test of conceptual implicit memory, was better at the midluteal than the follicular phase. In contrast, performance on a test of explicit memory, category-cued recall, did not vary across the menstrual cycle. At Session 1, women in the follicular phase performed better on the fragmented object identification task than did those in the midluteal phase. This unexpected finding suggests that high levels of ovarian hormones might inhibit perceptual object priming. Results confirmed previous reports of decreased mental rotations and improved motor skills and fluency in the midluteal phase. Estradiol levels correlated positively with verbal fluency and negatively with mental rotations and perceptual priming, which suggest that estrogen, and not progesterone, was responsible for the observed changes in cognition. Mood did not vary across the cycle phases. Overall, the findings suggest that estrogen may facilitate the automatic activation of verbal representations in memory.