New research by scientists at the University of Cambridge suggests that the neurotransmitter serotonin, which acts as a chemical messenger between nerve cells, plays a critical role in regulating emotions such as aggression during social decision-making.
Serotonin has long been associated with social behavior, 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. The research also provides insight into clinical disorders characterized by low serotonin levels, such as depression and obsessive compulsive disorder (OCD), and may help explain some of the social difficulties associated with these disorders.
These findings highlight why some of us may become combative or aggressive when we haven’t eaten.The only way to build serotonin in the brain is by consuming tryptophan in our diet, through foods such as poultry or chocolate. Serotonin levels are lower when a person has not eaten. Since serotonin levels naturally decline when we don’t eat, the researchers took advantage of this effect in designing their experiment.
- 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.
These results suggest that serotonin plays a role in social decision making.
- Normally, serotonin keeps aggressive social responses in check.
- Changes in diet and stress cause fluctuations in serotonin levels, and this study suggests that the fluctuations in serotonin affect every day decision-making
- This study suggests that patients with depression and anxiety disorders may benefit from therapies that teach them strategies for regulating emotions during decision making, particularly in social scenarios.
This research was funded by the Wellcome Trust and the Medical Research Council.