Neuroscience is one of the most skewed fields when it comes to testing on female physiology. One review found single-sex brain studies using male animals outnumbered those using females 6.7 to one. Aarthi Gobinath, a neuroscientist at the University of British Columbia, calls this a “hidden gap” in her field. She says there’s reason to question the assumption that the brains of males and females are identical, particularly in unique states like pregnancy.