Excerpt from The Female Brain

Because of her ability to observe and feel emotional cues, a girl actually incorporates her mother's nervous system into her own. Sheila came to me wanting some help dealing with her kids. With her first husband she had two daughters, Lisa and Jennifer. When Lisa was born, Sheila was still happy and content in her first marriage. She was an able and highly nurturing mother. By the time Jennifer was born, eighteen months later, circumstances had changed considerably. Her husband had become a flagrant philanderer. Sheila was being harassed by the husband of the woman he was having an affair with. And things got worse. Sheila's unfaithful husband had a powerful and rich father, who threatened to have the children kidnapped if she tried to leave the state to be with her own family for support.

It was in this stressful environment that Jennifer spent her infancy. Jennifer became suspicious of everyone and by age six started telling her older sister that their kind and beloved new stepfather was certainly cheating on their mother. Jennifer was sure of it and repeated her suspicions frequently. Lisa, finally went to their mom and asked if it were true. Their new stepfather was one of those men who just didn't have it in him to cheat, and Sheila knew it. She couldn't figure out why her younger daughter had become so anxiously fixated on the imagined infidelity of her new husband. But Jennifer's nervous system had imprinted the unsafe perceptual reality of her earliest years, so even good people seemed unreliable and threatening. The two sisters were raised by the same mother but under different circumstances, so one daughter's brain circuits had incorporated a nurturing, safe mom and the other's a fearful, anxious one.