When mothers are exposed to trauma, illness, alcohol or other drug abuse, these stressors may activate a single molecular trigger in brain cells that can go awry and activate conditions such as schizophrenia, post-traumatic stress disorder and some forms of autism. Until now, it has been unclear how much these stressors have impacted the cells of a developing brain. Past studies have shown that when an expectant mother exposes herself to alcohol or drug abuse or she experiences some trauma or illness, her baby may later develop a psychiatric disorder later in life. But the new findings identify a molecular mechanism in the prenatal brain that may help explain how cells go awry when exposed to certain environmental conditions.