The critical period hypothesis of estrogen effects on cognition: Insights from basic research

Background: In addition to its primary role in reproduction estrogen impacts brain areas important for cognition, including the hippocampus and prefrontal cortex. It has been hypothesized that decline in estrogen levels in women following menopause is associated with, or can exacerbate, age-related cognitive decline. However, clinical evidence to support a role for estrogen in preventing cognitive decline in women as they age is equivocal. The critical period hypothesis of estrogen effects on cognition, which proposes that estrogen administration has to be initiated within a critical time period following the loss of ovarian function in order for it to exert positive effects on the central nervous system, is offered as one explanation for inconsistencies across studies. Scope of review: This review details results from basic research using rodent models investigating the effects of estrogen on cognition in the aging female. Emphasis is placed on work investigating effects of timing of initiation of estrogen administration on its subsequent efficacy. Major conclusions: Results of basic research provide support for the critical period hypothesis. Furthermore, results of work in rodent models suggest mechanisms by which the response to estrogen is altered if treatment is initiated following long-term ovarian hormone deprivation. General significance: Understanding if and under what conditions hormone administration following the loss of ovarian function positively affects the brain and behavior could have important implications with regard to female cognitive aging. Results of basic research can contribute to this understanding and provide insight into the complex mechanisms by which estrogen affects cognition. (C) 2010 Elsevier B.V. All rights reserved.