The recent issue of the journal Hippocampus has an interesting article on the structure of the hippocampus throughout the menstrual cycle. By studying women two times during the menstrual cycle (pre- and post-menstrual) using volumetric MR scanning, researchers Xenia Protopopescu and her colleagues at Cornell University demonstrated structural changes in the hippocampus. Specifically, gray matter was relatively increased in the right anterior hippocampus and relatively decreased in the right dorsal basal ganglia (globus pallidus/putamen) in the postmenstrual phase.
Below is an image from that article, showing a t-map rendering showing increased anterior hippocampus (yellow) and decreased basal ganglia (pink) in the postmenstrual vs. premenstrual phase. Seems to me that the entorhinal cortex was also affected
Correspondingly, verbal declarative memory changed throughout the cycle: memory performance increased in teh postmenstrual vs. premenstrual phase. These results support models of estrogen-dependent cyclical alterations in hippocampal synaptic density and function proposed to account for neuronal and cognitive differences seen across the menstrual cycle.
The basal ganglia findings were rather unexpected, and the researchers suggest that:
(…) estrogens have been shown to increase striatal dopamine release, to inﬂuence striatal serotonergic and dopaminergic innervation density, and to promote striatal medium size spiny neuronal maturation in vivo (Korol, 2004b). The apparent opposite effect of high estrogen levels on hippocampal and basal ganglia gray matter may relate to the ﬁnding in rats that high estrogen promotes use of a hippocampally-mediated spatial (place or allocentric) learning strategy, while low levels promote use of a nonhippocampal, possibly striatally-mediated navigational (response or egocentric) strategy (Korol, 2004b). In humans, MRI studies have shown that navigational ability correlates with level of activity in the basal ganglia (putamen) (Epstein et al., 2005), and more speciﬁcally, that navigation using a response strategy is associated both with greater activity (Iaria et al., 2003) and gray matter (Bohbot et al., 2007) in the basal ganglia (caudate), though it should be noted that menstrual cycle effects were not assessed in any of these studies.
I can imagine the jokes that may come out of this… but leave it for now 😀 One thing that strikes me is the question of how these changes are related to the menopause. For example, would these changes mean that intra-individual variation during the month would be reduced after the menopause? As one knows from ageing research, such variance increases with age. So it is even conceiveable that the development goes the opposite way.
I also notice that the same researchers have recently demonstrated a link between changes in orbitofrontal cortex and emotional processing. It’s also worth a read.