Dopamine Equals ‘Don’t Be Mean’?

By Neuroskeptic | November 14, 2013 3:57 am

Men whose brains generate and store more dopamine are less prone to aggression, according to a group of German researchers: The Impact of Dopamine on Aggression: An [18F]-FDOPA PET Study

To quantify how aggressive the participants were, the researchers got them to play a game, for cash, in which a selfish ‘opponent’ sometimes stole their money. The player could choose to take revenge by pressing a button that, they thought, would punish the opponent (who didn’t really exist – it was all the computer.) Meanwhile, they had to repeatedly press a different button to earn cash.

Dopamine metabolism was measured with positron emission tomography (PET) using the radioactive [18F]-FDOPA tracer.

When they looked at the brain-behaviour correlations, the results were pretty impressive:

dopam

Dopamine (FDOPA concentration) was inversely correlated with aggressiveness across various brain regions (thalamus, midbrain and caudate). More dopamine, less revenge.

Now when I picked this paper up, I was skeptical (shock!) and I thought: this seems too good to be true; did they just run lots of comparisons, and focus on the most significant ones?

Well, they say they did do 12 different dopamine-aggressiveness correlations, because they measured dopamine in 4 brain areas, and 3 aspects of dopamine metabolism. However, correcting for those 12 comparisons still left one standing: the relationship between dopamine synthesis capacity (K) in the midbrain region, and aggression. The correlation coefficient here was a formidable rho = -0.64.

That’s a strong link in any context, but in the world of brain-behaviour correlations it’s remarkable. Still, it’s significant.

The effect is rather unexpected however – you might predict that more dopamine would mean more aggression, because antipsychotics (used as tranquillizers) block dopamine transmission while cocaine and amphetamines, which increase dopamine levels, are popularly known for making people erratic and violent. This is also what animal research suggests.

ResearchBlogging.orgSchlüter T, & et al (2013). The Impact of Dopamine on Aggression: An [18F]-FDOPA PET Study in Healthy Males. The Journal of Neuroscience, 33 (43), 16889-96 PMID: 24155295

CATEGORIZED UNDER: animals, drugs, papers, select, Top Posts
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  • http://bekolay.org/ Trevor Bekolay

    I haven’t read the paper, so this may be addressed in the text, but just looking at those correlation plots, I wonder what the statistics would be without that outlier at the top-left.

  • FdUquillas

    Interesting. Though this shouldn’t be interpreted as more dopamine equals less aggressive behavior. This study, in my opinion, simply reinforces the concept that there’s a favorable dopamine synthesis capacity range.
    If I gave someone with a putative low dopamine synthesis capacity a dopaminergic (which would enhance dopaminergic tone in the circuitry) I would expect an enhancement effect in working memory capacity, reduction in impulsivity, and other PFC-related processes. However, if someone with a normal or higher than average dopamine synthesis capacity is given a dopaminergic, this would cause a ‘overdosing’ of the PFC and actually negatively affect PFC-related processes including inhibitory control (in this context, impulsive aggression).

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  • Malibu Healer

    Cocaine and amphetamine users are erratic and violent because of a lack of REM sleep, not from the drugs themselves.

  • Jona Sassenhagen

    Bonferroni p = 0.004. Midbrain correlation p after dropping the single gigantic outlier: 0.006.
    Now, I’m not a big fan of bonferroni, or their statistical approach in general, but by their own measure, their result is not significant. (Which mainly shows how dumb bonferroni is, because r ~.5 is “significant” by any sensible means. It’s just, they rather should’ve given a CI around the outlier-removed, possibly corrected r.)

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  • Nick Stuart

    What is the ‘normal’ level of dopamine in the brain? Do some people have less or more than normal? What does the science say?

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About Neuroskeptic

Neuroskeptic is a British neuroscientist who takes a skeptical look at his own field, and beyond. His blog offers a look at the latest developments in neuroscience, psychiatry and psychology through a critical lens.

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