Serotonin levels -- a hormone that helps regulate behavior -- fluctuate when people are stressed out or haven't eaten.
The study in the journal Biological Psychiatry says rising and falling serotonin levels affect parts of the brain that allow people to control their anger.
The study found low levels of serotonin made communications between certain parts of the brain weaker than normal. They say when that happens it may be harder for the brain to control emotional responses to anger.
The findings could be applied to a range of psychiatric disorders in which violence is the common problem.