What does it mean when a woman commits a crime and attributes her actions to PMS? We revisit the first use of the "PMS defense" in this country, back in 1981. What have we learned about the science of PMS since then? Last year, the American Psychiatric Association classified a form of PMS (Premenstrual dysphoric disorder, or PMDD) as a mental disorder in the DSM-V. How can the scientific community study severe premenstrual symptoms without perpetuating the utterly unscientific idea that menstruating women aren’t mentally competent or liable for crimes they commit? We talk to lawyer Stephanie Benson who used PMS as a defense for her client Shirley Santos after Santos was charged with assault and endangering her children.