In two recent studies published in NeuroImage (and cover story of NeuroImage Vol. 220), assistant professor Emily Jacobs and her team collected dense-sampling, multimodal brain imaging data probing the extent to which endogenous fluctuations in sex hormones across a complete reproductive cycle – 28 days – alter brain gray matter volume and functional connectivity of brain networks at rest.

One of the studies aims to understand changes in the hippocampus and its cortical input pathways as a function of the level of progesterone. Using oral contraceptive to causally and selectively manipulate the level of progesterone, the researchers found no changes in gray matter volume in the participant. During memory formation, the parahippocampal versus perirhinal cortices receive information from different sensory processing pathways and convey it to the hippocampus, so progesterone may promote a bias toward memories for certain types of information. The findings have implications for aging as well as many psychiatric and neurological disease models, which show associations with hippocampal gray matter loss. This work is highlighted in Science Translational Medicine

The other study addresses the unknown question of how sex hormones influence on the functional architecture of the human brain. This study illustrates estrogen and progesterone’s widespread associations with functional connectivity. Time-lagged analyses examined the temporal directionality of these relationships and suggest that cortical network dynamics are preceded—and perhaps driven—by hormonal fluctuations. These results reveal the rhythmic nature in which brain networks reorganize across the human menstrual cycle.