Brain memory modifies wiring during the female menstrual cycle

Researchers at Northwestern University and Columbia University have found that "wiring" in female rat brain memory area expands and retracts in relation to the amount of estrogen present during the estrous/menstrual cycle.

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.