When his criminal trial begins next week, attorneys for Andres Andy Avalos, a Florida man charged with murdering his wife, a neighbor and a local pastor, will mount an insanity defense on behalf of their client because, as they announced last summer, a PET scan revealed that Avalos has a severely abnormal brain. In March, shortly after an Israeli American teenager was arrested on suspicion that he made bomb threats against Jewish institutions in the U.S. and abroad, his lawyer declared that the teenager had a brain tumor that might have affected his behavior. Both cases are part of a growing movement in which attorneys use brain damage in service of a legal defense.

To support such claims in court, lawyers are turning to neuroscience. The defense brings in hired guns to testify that brain scans can identify areas of dysfunction linked to antisocial behavior, poor decision-making and lack of impulse control. The prosecution calls their own expert witnesses to argue that what a scientist might observe in brain scans shows nothing about that persons state of mind or past actions.

The truth is that even the most sophisticated brain scans cannot show direct correlations between brain dysfunction and specific criminal behavior, nor can they prove whether someone is legally insane. What neuroscience can show is that a persons decision to commit a crime or to do anything in life for that matter is triggered by a series of chemical and electrical interactions in the brain. It can also show approximately where those interactions are occurring.

Consider the case of Charles Whitman, who killed 14 people from a perch atop the Texas Tower at the University of Austin in 1966. (He killed his wife and mother the night before.) In a note he left before going on his killing rampage, Whitman wrote of having severe headaches and suggested that an autopsy might reveal a physical anomaly.

He had a brain tumor, it turned out, the size of a pecan. It was nestled between the thalamus, which relays sensory and motor information and regulates sleep, and the amygdala, which is associated with emotional regulation and behavior. Many of Whitmans family members and friends wanted to believe the tumor was responsible for triggering his actions. Yet a doctor reported that he didnt think the tumor was related to Whitmans psychiatric complaints or headaches, and certainly not to his homicidal rampage.

Texas Gov. John Connally called a state commission to review Whitmans case. In its final report, the commission allowed that the tumor conceivably could have contributed to his inability to control his emotions and actions, but said that it could not establish that the tumor actually caused the killings.

The tumor, then, didnt change Whitmans standing. As long as a person understands the difference between right and wrong and can appreciate the nature and consequences of his or her actions, he or she cannot be found legally insane. Whitmans crimes took care, planning and forethought. It would have been impossible to prove that the tumor qualified him as legally insane.

Its not yet clear if the lawyer representing the Israeli American suspect will submit evidence of his brain tumor in court, but it is clear that the teens actions required forethought and premeditation. He used Tor, a type of software that allows users to hide their computers identifying IP address. He also disguised his voice, an indication that he knew what he was doing and that there would be consequences if he was caught.

Though decades of research tell us that brain damage can alter peoples behavior and impair their ability to make sound judgments and rational decisions, in the legal realm, thats not enough for a successful criminal defense. There is, however, one limited area in which neuroscience can be applied appropriately and responsibly in the courtroom: sentencing.

Our judicial system has long recognized that people who suffer from psychiatric or mental illnesses should not be treated in the same way as their mentally healthy counterparts. Medical diagnoses of psychiatric conditions or cognitive impairment are considered mitigating circumstances that raise the possibility of alternatives to harsher punishments. Neuroscientific evidence can be used to support such diagnoses.

Although the legal system should recognize the value of neuroscience, it must also understand its limitations and guard against its abuse. When neuroscience is applied responsibly, it can mean treatment instead of incarceration, life instead of the death penalty.

Kevin Davis is a Chicago-based journalist and author of The Brain Defense: Murder in Manhattan and the Dawn of Neuroscience in Americas Courtrooms.

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Why are lawyers using brain damage as a criminal defense? The science doesn't support it - Los Angeles Times