DO YOU immediately lash out in anger at anyone who criticises you? Or do you mull about it, then take your anger out on innocent victims such as your partner, or another driver on the road?

In the first study of its kind, Sydney researchers have insulted people while scanning their brains and discovered that different regions become active depending on which type of aggressive response a person usually has.

Tom Denson, of the University of NSW, said his team's research might eventually make it possible to determine aggressive tendencies from a simple brain scan. "What is particularly fascinating is that within seconds of being insulted, personality influences which brain regions light up," Dr Denson said.

Aggression had advantages in earlier times. "Think of Genghis Khan. He was extremely aggressive and had many mates and many children."

But in modern society people needed to control this harmful behaviour. "It causes more problems than it has benefits," he said.

Other anger studies have monitored brain reactions to angry faces or memories of upsetting events.

Yet personal provocation is the leading cause of aggressive behaviours such as homicide, aggravated assault and bitter disputes.

"This is the first study to have a realistic provocation, something that might happen in daily life," Dr Denson said.

The unsuspecting participants were asked to solve anagrams and state their answer out loud. On three occasions a researcher asked them to speak up, then finally said in a condescending, rude tone: "Look, this is the third time I have had to say this. Can't you follow directions?"

The 20 participants had previously been tested for personality type. Those who said they often felt intense anger and retaliated with impulsive aggression showed increased activity in a brain region known as the dorsal anterior cingulate cortex after being insulted.

Whereas the ruminators with "displaced aggression" showed increased activity in a different region, the medial prefrontal cortex, which is associated with awareness of negative moods.

The study is to be published in the Journal of Cognitive Neuroscience . Dr Denson said mental distraction was a good way to avoid flying off the handle when criticised or insulted, which was not a wise strategy.

"Something as easy as a word search puzzle can take your mind off it while you wait for the physiological arousal to come down."

Angry feelings usually dissipated within 10 to 15 minutes, he said, when a more rational response was possible.