Kansas City, Mo. ? A woman accused of killing an expectant mother and cutting the baby from her womb believed so strongly that she was pregnant that she likely went into an out-of-body state when that belief was threatened, an expert testified Tuesday.

Dr. Vilayanur Ramachandran, director of the Center for Brain and Cognition at the University of California, San Diego, said Lisa Montgomery suffered from pseudocyesis, which causes a woman to falsely believe she is pregnant and exhibit some of the outward signs of pregnancy.

Montgomery has pleaded not guilty to kidnapping resulting in death, and her attorneys are pursuing an insanity defense. They contend she suffered from several mental illnesses, including post-traumatic stress disorder brought on by childhood sexual abuse, when she killed Bobbie Jo Stinnett, 23, at her Skidmore home on Dec. 16, 2004.

Ramachandran said the sexual abuse and resulting post-traumatic stress disorder may have predisposed Montgomery to pseudocyesis.

The condition triggers hormonal and physical changes that reinforce the pregnancy delusion, he said. To further heighten the appearance of pregnancy, people suffering from pseudocyesis will swallow air and stick out their bellies but not realize they are doing so, Ramachandran said.

They also may manufacture evidence and obsess about the delusional pregnancy. Doctored ultrasound photos that Montgomery showed off were consistent with the disorder, as were frequent Internet searches for pregnancy, he said.

When the pregnancy belief is threatened, people suffering from such delusions may go into an out-of-body, dissociative state, Ramachandran said. One such threat occurred when Montgomery’s ex-husband, Carl Boman, told her he suspected she was faking a pregnancy and he planned to use it against her in a custody fight.

Montgomery told Ramachandran that on the day of the killing she had gone to Stinnett’s house because both raised rat terriers and Montgomery wanted to breed one of her dogs with one of Stinnett’s dogs.

She told him she couldn’t remember the exact sequence of events. But she recalled trying to rouse Stinnett and cutting the baby’s cord with a knife.

Asked whether Montgomery would have understood what she was doing when she killed Stinnett, he explained that, “You are a spectator, so in a sense you are not really there.”

The court adjourned before the prosecution had a chance to cross-examine Ramachandran.

Also Tuesday, a psychiatrist testified that Montgomery told her she gave birth three days before the crime and buried her baby near her Kansas home.

Dr. Linda McCandless, who has been treating Montgomery since she was arrested in December 2004, also testified that Montgomery believed she was pregnant starting in April 2004, saying she had gained 25 pounds, had morning sickness and that she stopped menstruating.

McCandless testified that Montgomery told her that she had delivered a baby on Dec. 13, 2004, and “I may not have done anything and let the baby die.”

Montgomery claimed to have buried the baby on her property in Melvern, Kan., and said she thought the body was still there, McCandless said.

McCandless said when she interviewed Montgomery in December 2004, Montgomery did not remember the murder. McCandless said Montgomery told her, “She must have done it because she had that baby” and that if she did do it, “I deserve to die.”