PET Scans Link Low Dopamine Levels and Aggression

PET imaging has demonstrated a link between low dopamine levels and aggression in young healthy adults - surprisingly opposite results from what was previously hypothesized, said researchers in a presentation at the Society of Nuclear Medicine’s Annual Meeting, in Miami Beach, Fla., this week.

The neurobiology of aggression is not well understood, but researchers have been aware that there is a relationship between serotonin, a neurotransmitter, and certain aggressive behaviors. To investigate this further, researchers from RWTH Aachen University in Aachen, Germany, assessed 18 healthy adults in their 20s for aggression using the psychological behavioral task known as point subtraction aggression paradigm (PSAP). They wanted to determine if higher levels of dopamine, involved in pleasure and reward, increased aggressiveness, but the results weren’t as theorized.

By playing a computer game, in which the participants were told that an opponent in another room would be able to cheat and steal some of the participants’ winnings, the subjects could punish the cheater (who did not exist in reality), shield against the adversary by repeatedly pressing a defense button, or continue to play the game in order to maximize their ability to win cash. This indicated resilience.

The subjects underwent PET scanning with F-18 FDOPA, a biomarker that lights up enzymes’ ability to synthesize serotonin. The uptake was analyzed to gauge the correlation between the subjects’ dopamine synthesis capacity and aggressive behavior.

The researchers found that there was a significant impact on aggressive response in areas in the brain where dopamine synthesis was present, especially in the basal ganglia, which among other functions, include the motivation center. Minimized aggression was associated with higher dopamine levels in both the midbrain and the striatum, which plays a role in planning and investigative functioning.

Focus on the monetary reward aspect of the PSAP was seen among subjects with a greater capacity for dopamine synthesis, while those with lower capacities had higher vulnerability to act either aggressively, defensively, or both, researchers said.

“We think that a well-functioning reward system causes more resilience against provocation,” said lead author Ingo Vernaleken, MD. “However, we cannot exclude that in a situation where the subject would directly profit from aggressive behavior, in absence of alternatives, the correlation may be the other way around.”