Finally, there exists a causal link between serotonin and impulsivity. The neurotransmitter serotonin is a chemical messenger in the brain that regulates emotions and it has often been associated with social decision-making.
Scientists at the University of Cambridge have shed more light on the ‘myth’ that people tend to become aggressive when they are hungry. Our serotonin levels decline when we do not eat because the essential amino acid used to create serotonin can be found in food, such as tryptophan rich products like poultry and chocolate.
The researchers of the study, funded by the Wellcome Trust and the Medical Research Council, manipulated the subjects’ diet in order to reduce serotonin levels. They then used the ‘Ultimatum game’ to study the subjects’ reactions to unfair behaviours. In this game, a player suggests a manner in which to divide a sum of money into two portions, one for themselves and another for the other player. If the other player agrees on the split they each keep their agreed-upon portion. If the other player disagrees with the split then no one gets paid. Typically, people tend to reject 50% of offers that are less than 20-30% of the total stake. However, with lowered serotonin, rates of rejection increased to over 80%. As per Molly Crockett, PhD student at Cambridge Behavioural and Clinical Neuroscience Institute:
"Our results suggest that serotonin plays a critical role in social decision-making by normally keeping aggressive social responses in check. Changes in diet and stress cause our serotonin levels to fluctuate naturally, so it’s important to understand how this might affect our every day decision-making" - Article
Now that proof exists that serotonin, which is manufactured through diet, affects the impulsivity of decision-making, it would be interesting to examine how this might apply to other situations involving choices, such as how much impact serotonin levels have on decision-making among users of cocaine, a known appetite suppressant.