A trip down memory lane about sex differences in the brain.

Scientific studies funded by the United States government must now include both males and females as experimental subjects. This is a welcomed change for those of us who have been reporting on sex differences for decades. That said, there are some issues to consider; I focus on one in this review: females used in animal models of mental illness and health are almost always virgins and yet most adult females around the world, irrespective of species, are not virgins. I am not advocating that all scientists include non-virgin females in laboratory studies, but rather to consider the dynamic nature of the female brain when drawing conclusions through discovery. Stressful life experiences, including those related to sexual aggression and trauma, can have a lasting impact on processes of learning related to mental health and plasticity in the female brain. Her response to stress can change rather dramatically as she emerges from puberty to become pregnant and produce offspring, as she must learn to care for those offspring. The inclusion of females in scientific research has been a long time coming but it comes with a history. Going forward, we should take advantage of that history to generate hypotheses that are both reasonable and meaningful.