Psychiatric diagnoses of the condition, known formally as Intermittent Explosive Disorder (IED) are rare. But Mary Best at the Children's Hospital of Philadelphia says: "Even individuals who do not meet full criteria for the disorder can still have frequent uncontrollable episodes of impulsive aggression, and they can impact society through their violent behaviour. An example would be a spousal abuser."

The disorder usually starts in adolescence, and most cases probably go undiagnosed, says Best. Some psychologists have blamed IED episodes for recent cases of school pupils massacring fellow students.

This is the first study to find a deficit in a particular brain region in patients with IED, says Best. She thinks the work could lead to new behavioural treatments.

Persistent losers
 

Best and colleagues studied 24 IED patients, along with 22 control subjects. They were given a battery of tests designed to evaluate functioning of the orbital/medial prefrontal cortex circuit, which is linked to impulse control and emotion processing.

"For example, we used a gambling task. And across 100 trials, control subjects learned to avoid 'disadvantageous decks' - decks that would result in a net loss of fake money. But IED subjects picked at the same rate throughout the task," says Best.

This supports the idea that the patients have difficulty learning to consistently avoid making choices associated with a high level of punishment. So they may use aggression as a problem-solving strategy, even though they run the risk of injury or imprisonment.

Facial expressions
 

IED patients were also less successful at judging facial expressions. "They were impaired at recognising negative expressions - anger and disgust, and biased to label neutral expressions with negative emotions," Best says.

The work suggests that teaching patients to judge facial expressions more accurately, or at least to recognise deficiencies associated with triggering angry outbursts, might help treatment, says Best.

The underlying cause of the orbital/medial prefrontal cortex dysfunction is not known. But previous research has shown that some IED patients respond to treatment with selective serotonin reuptake inhibitors - such as Prozac, more commonly used to treat depression. This implicates low levels of serotonin in the disorder.

Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.112604099)

Emma Young

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