The old saying that a woman has “men on the brain” can be accurately supplanted by saying that many women have men IN the brain. This study explains the biological facts:
“Male microchimerism in the human female brain,” William F.N. Chan, Cecile Gurnot, Thomas J. Montine, Joshua A. Sonnen, Katherine A. Guthrie [pictured here], and J. Lee Nelson, PLoS One, vol. 7, no. 9, 2012, e45592. the authors, at the Fred Hutchinson Cancer Research Center, Seattle, and at the University of Washington, report:
“In this study, we quantified male DNA in the human female brain as a marker for microchimerism of fetal origin (i.e. acquisition of male DNA by a woman while bearing a male fetus)…. We report that 63% of the females (37 of 59) tested harbored male microchimerism in the brain. Male microchimerism was present in multiple brain regions…. In conclusion, male microchimerism is frequent and widely distributed in the human female brain.”
BONUS: The 2005 study “Male microchimerism in women without sons: quantitative assessment and correlation with pregnancy history,” which says: “Male microchimerism was not infrequent in women without sons.”
BONUS [only distantly related]: One of the studies honored by the 2015 Ig Nobel Medicine Prize reports how male DNA, obtained via a lengthy, intimate kiss, can sometimes be found in the saliva of the female who engaged in that kiss. That study is “Prevalence and Persistence of Male DNA Identified in Mixed Saliva Samples After Intense Kissing.”