A study describing this research will be presented on Nov. 14 by Aryeh Routtenberg, professor of psychology, neurobiology and physiology at Northwestern University, at the 2005 Society for Neuroscience Meeting in Washington, D.C.
Because this area of the brain, the hippocampus, has been shown to be critical to both humans and animals for memory processes, the group's finding lends support to a vast array of empirical and anecdotal evidence concerning variations in cognition and memory processes as a function of the time of the female cycle.
That this rewiring is due to estrogen was shown in experiments using hormone replacement therapy to compare females with low, moderate or high levels. Only when the high physiological level was reached - similar to that seen during the peak of estrogen levels during the estrous cycle - was the growth observed.
The investigators suggest the provocative hypothesis that the ability of the female brain network to modify itself in the presence of increased estrogen may facilitate processing of complex spatial environments to enhance reproductive success, for example, selecting a mate or, as a mother, finding food, water and shelter while avoiding predators.
"Beyond the findings relative to estrogen, and its regulation of female cognition, the results of the study suggest that the brain's capacity for growth is well beyond anything we considered in the past," said Routtenberg, who is director of The Cresap Neuroscience Laboratory and a researcher at the Northwestern University Institute for Neuroscience.
"This growth also occurs during learning, but it is a much slower process," Routtenberg said.
Earlier research has shown that learning encourages growth of mossy fibers, which are axons, or nerve fibers, in the hippocampus. Mossy fibers are unique because they have high concentrations of zinc and the cells that give rise to these axons, the granule cells, show neurogenesis, or birth of new nerve cells in adults.
Northwestern post-doctoral student Matthew R. Holahan and Helen E. Scharfman and members of her laboratory at Helen Hayes Hospital, Columbia University, New York collaborated on this work.
This research was supported by grants MH 65436 from the National Institutes of Health; IBN 0090723 from the National Science Foundation; NS 37562; and TB AG 20506.