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New Study Touts Link Between Serotonin and Impulsivity and Decision-Making

Posted Oct 03 2008 12:52pm

According to this article, new research confirms the relationship between low levels of the neurotransmitter serotonin and the management of emotions during social decision-making. While the impact of serotonin on emotions has been long suspected (and argued about), the authors of this study claim they have documented the link between the two, at least with respect to their particular findings. From the article:

Serotonin has long been associated with social behaviour, but its precise involvement in impulsive aggression has been controversial. Though many have hypothesised the link between serotonin and impulsivity, this is one of the first studies to show a causal link between the two.

According to the article, the researchers manipulated the level of serotonin by withholding food. As serotonin is made, in part, through the use of an amino acid available only by food intake, subjects had their serotonin levels reduced in this manner:

Their findings highlight why some of us may become combative or aggressive when we haven't eaten. The essential amino acid necessary for the body to create serotonin can only be obtained through diet. Therefore, our serotonin levels naturally decline when we don't eat, an effect the researchers took advantage of in their experimental technique.

The experiment then proceeded to measure how the reduced level of serotonin impacted the subject’s sensitivity to unfair social responses (based on a research game):

The researchers were able reduce brain serotonin levels in healthy volunteers for a short time by manipulating their diet. They used a situation known as the 'Ultimatum Game' to investigate how individuals with low serotonin react to what they perceive as unfair behaviour. In this game one player proposes a way to split a sum of money with a partner. If the partner accepts, both players are paid accordingly. But if he rejects the offer, neither player is paid.

Normally, people tend to reject about half of all offers less than 20-30% of the total stake, despite the fact that this means they receive nothing - but rejection rates increased to more than 80% after serotonin reductions. Other measures showed that the volunteers with serotonin depletion were not simply depressed or hypersensitive to lost rewards.

This would be an article definitely worth reviewing in its entirety. Specifically, I would like to learn how the researchers were able to link the results specifically to reduced serotonin levels. I can understand the cause-effect differences based on change in food intake, but how could the authors isolate the results to serotonin levels based on a reduction in food? Let me rephrase - Are there any other changes that occur as a result of a change in food intake besides a change in serotonin levels? I am genuinely curious, as I don’t know enough about the neuroscience behind this. I would think, though, that the body undergoes changes in the levels of multiple chemicals during a food restriction, and I would also imagine those changes may also impact one’s emotional control. Without knowing further, would expect the next step be to assessing the amount of the change being due to a drop in serotonin, rather than an assumption that it is all due to serotonin. But again, I guess I’d have to read the article first!

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