People prone to road rage and other outbursts of anger have smaller emotional brains, according to a new study.
Neuroimaging studies suggest that frontolimbic regions of the brain, the parts that regulate emotions, play a role in aggressive behaviour.
Now, it seems that people with intermittent explosive disorder (IED) have significantly lower amounts of grey matter in these regions of their brains.
The study, published in the journal Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, collected MRI scans of 168 subjects, a mixture of people with and without IED along with 58 control subjects.
The team found a direct correlation between those with a history of aggressive behaviour and the level of reduction in grey matter volume.
Study lead author Dr. Emil Coccaro, of the University of Chicago, said: "Intermittent explosive disorder is defined in DSM-5 as recurrent, problematic, impulsive aggression.
"While more common than bipolar disorder and schizophrenia combined, many in the scientific and lay communities believe that impulsive aggression is simply 'bad behavior' that requires an 'attitude adjustment.'
"However, our data confirm that IED, as defined by DSM-5, is a brain disorder and not simply a disorder of 'personality.'"
Dr. Cameron Carter of the University of California, who is editor of the journal that published the study, said: "These important findings suggest that disrupted development of the brain's emotion-regulating circuitry may underlie an individual's propensity for rage and aggression."