NEW YORK — Lawyers for a New York writer accused of kidnapping and assaulting a former colleague showed colorful images of the defendant's brain in court Thursday to support their assertion that he suffered from a mental illness that prevented him from forming criminal intent.

Shortly after Manhattan prosecutors rested their case Thursday afternoon against Peter Braunstein, his lawyers called a psychiatrist to explain the results of a brain scan that he performed on the defendant in April 2006.

Braunstein, 43, admits his involvement in the Halloween 2005 attack on the woman, a former colleague at Fairchild Publications. He has pleaded not guilty to a 13-count indictment stemming from the incident and blames his actions on undiagnosed schizophrenia.

Dr. Monte Buchsbaum, a professor of psychiatry at Mt. Sinai School of Medicine, testified that he performed a PET scan on Braunstein to look for abnormal activity in his brain.

Buchsbaum, a pioneer in the research field of PET-scan technology, said that images of the activity in Braunstein's brain were consistent with a diagnosis of schizophrenia.

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As the doctor stood next to PET-scan images comparing Braunstein's brain to a "normal" brain, he pointed out to the jury light-blue areas in Braunstein's brain, which he said were indicative of low levels of metabolism compared to the other brain.

Buchsbaum said that the "marked" deficiency would affect Braunstein's frontal lobe, which dictates, among other things, the brain's capacity for making "executive decisions," planning, impulse control and making moral judgments.

The alleged deficiency is crucial to the success of Braunstein's defense strategy, which requires that a jury find he was incapable of conscious decision-making the day of the incident and in the months before, while he planned the attack.

"How does it affect the ability to plan, based on what you saw?" defense lawyer Robert Gottlieb asked the witness.

"An individual with severe injuries to the frontal lobe typically exhibits deficiencies in that area," Buchsbaum testified. "These deficits are commonly associated with schizophrenia."

Under cross-examination, Buchsbaum defended the reliability of the PET scan, which assistant district attorney Shanda Strain attacked for its lack of conclusive findings on its own.

The controversial procedure has been used in other recent criminal cases to attempt to explain deviant behavior. Lawyers for Florida sex offender John Couey presented similar PET-scan evidence at his capital murder trial for raping and killing 9-year-old Jessica Lunsford. An expert witness for Couey testified that the scan showed uneven brain formation in his frontal lobe which affected his ability to form sound judgment. Couey was ultimately convicted and sentenced to death.

Braunstein's expert conceded that the results alone were not enough to make a formal diagnosis of schizophrenia. He also testified that the mere showing of low levels of metabolism in the frontal lobe did not automatically imply a diagnosis of schizophrenia.

Lawyers for Braunstein are expected to call another doctor who will corroborate Buchsbaum's claim by making a clinical diagnosis of schizophrenia.

Braunstein's lawyers will also have to overcome the word of his ex-girlfriend, Jane Larkworthy, who testified Wednesday that she never noticed signs that Braunstein suffered from hallucinations or paranoid delusions, two common symptoms of schizophrenia.

Larkworthy, whose two-year relationship with the defendant ended in 2003, accused Braunstein of subjecting her to emotional abuse and harassment, which only worsened after they broke up.

During cross-examination Thursday, she admitted that Braunstein never threatened her with physical violence, nor did she suspect that he would be capable of the acts he is accused of committing.

The defense case resumes Monday. Braunstein faces 25 years to life if convicted.