Neural AO3

• A strength is that there is support for the serotonin deficiency hypothesis for aggression in humans. Duke et al conducted a meta-analysis of 175 studies and found a small inverse relationship between aggression and serotonin levels. The magnitude of relationship varied over time and with self-reported aggression vs. other-reported aggression. However only other reported aggression positively correlated to serotonin functioning, suggesting the link between aggression and serotonin is more complicated than suggested
• Passamonti et al altered serotonin levels in participants by manipulating their diet to contain levels of tryptophan, which manufacture serotonin. They were assessed on a questionnaire and were given MRI scans when shown a series of faces with angry, sad and neutral expressions. On no tryptophan (low serotonin) days the communication between the prefrontal cortex and limbic system was weaker compared to normal tryptophan (normal serotonin) days. This would be particularly weak in those who were identified as aggressive on the questionnaire.