Brain PET image wins SNM 2007 Image of the Year honors

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WASHINGTON - A brain PET image that shows the correlation between radiotracer uptake and aggressive traits in men received Image of the Year honors at the SNM meeting this week. In announcing the recognition, Dr. Henry Wagner said it represents the growing ability of molecular imaging to illustrate the relationship between the mind and the brain.

Wagner presented the award to a group of researchers from Brookhaven National Laboratory in Upton, NY, who used PET to measure enzyme activity and its relationship with aggressiveness. The research was presented in a poster today at the SNM conference by Nelly Alia-Klein, Ph.D., of Brookhaven, with Dr. Nora Volkov, director of the National Institute on Drug Abuse, listed as a co-author on the paper.

"The Image of the Year reflects the fact that the chemistry of the brain is now being extensively measured in human beings using radioactive tracer techniques," Wagner said. "(These images) reflect moving further into the relating of brain chemistry to behavior."

The image was collected during a study of the relationship between an enzyme, monoamine oxidase A (MAO-A), and aggressive traits in men. MAO-A plays an important role in metabolizing neurotransmitters that affect human behavior, and the gene that regulates MAO-A activity has already been associated with aggressive and violent behavior for many decades, Alia-Klein said.

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Left, double-helix demonstrating MAO-A gene. Right, PET scan demonstrating uptake of clorgyline radiotracer, which matches levels of MAO-A enzyme in men tested for aggressiveness. Image courtesy of SNM.

For example, individuals with a genotype in which low MAO-A levels are produced tend to be more aggressive, while those with high MAO-A levels are less aggressive. However, few studies have been done of the MAO-A enzyme in the brain and how it specifically affects behavior.

Alia-Klein and co-researchers took a group of 38 healthy normal males and administered a standardized set of questionnaires measuring verbal and nonverbal intelligence, depression, and personality traits. The tests included questions that measured aggressiveness, such as whether the respondents frequently lost their temper or enjoyed watching violent movies. None of the men had violent backgrounds, she added.

The group then administered PET scans using clorgyline, a carbon-11-based radiotracer. They found that clorgyline uptake exactly matched previous knowledge of MAO-A's relationship with aggressiveness. The less aggressive men had higher clorgyline uptake, while the more aggressive men had lower clorgyline uptake.

What's more, no correlation was found between clorgyline uptake and any of the other variables that were measured, such as depression or negative emotions, Alia-Klein said.

"The varying degree of aggressive behavior corresponded to the varying degree of the MAO-A activity, and that's the correlation," Alia-Klein said. "It's really remarkable, because MAO-A is just a general enzyme, it's not something specific that no one has ever heard about."

The study has laid the groundwork for further studies of the link between MAO-A and aggressive behavior by establishing a baseline normal population. Alia-Klein next hopes to conduct a similar study of men who do have violent backgrounds, such as histories of domestic abuse. That study will also involve imaging, she said.

"I'll be doing (the same thing), but where the behavior is extreme, where the behavior is out of control," Alia-Klein said. "It's okay if some of us are more aggressive than others, but it's when you become violent that it becomes a public health issue."

By Brian Casey staff writer
June 5, 2007

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Copyright © 2007

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