Science is now suggesting aggression is more than just bad attitude and "explosive" brain responses may be at play. Gerry Byrne reports
Tennis player John McEnroe was famed for his uncontrolled angry outbursts at the umpire as much as for his brilliant playing. Alabama soccer mum Shirley Henson became the subject of a whole new chapter in the road rage saga when she shot dead another middle class woman, Gena Foster, after a minor traffic altercation in 1999.
But meet either person in a different situation and you would have remarked what wonderful, caring considerate people they were.
Yet they typify the people for whom a simple disagreement erupts into the prelude for World War Three. Their behaviour wrecks marriages, traumatises children, creates unhappy workplaces and sometimes leads to violence.
We characterise them as bad, undesirable people with unpleasant personalities but they are proving compelling subjects for study by some scientists who believe they may be on the threshold of major discoveries about how the brain operates.
Neuroscientists, the people who study biological brain functions, have discovered such significant differences in the brain chemistry of anger-prone patients to suggest they have discovered a new psychiatric disorder, intermittent explosive disorder, which may be more common than we think.
They have been probing the role of the various brain chemicals known as neurotransmitters which transmit signals across nerve endings known as synapses. So far they have discovered dozens of them, each one of which may be responsible for triggering or regulating different sensations or emotions.
Dr Emil Cocarro, professor of psychiatry at the University of Chicago, is one of the high priests of this new branch of psychiatry. He leaped to prominence for championing discoveries about one brain chemical, called 5-HT by scientists but better known as serotonin. He discovered people prone to impulsive and aggressive outbursts of anger had less serotonin in their brains than ordinary people.
His discoveries have been borne out by other studies, both in animals and humans. Dr Dee Higley, an American scientist studying a troop of monkeys, found that animals with low serotonin got into more fights, often scrapping pointlessly with stronger, more dominant monkeys.
In Ireland, Dr Ted Dinan, of University College Cork, then working at St James's Hospital, Dublin, participated in research among murderers at the Central Mental Hospital in Dublin which indicated they too seemed to have reduced serotonin. Volatile, angry people are often told they have hair-trigger tempers but Cocarro believes it's not the trigger, but the safety catch, that is at fault.
"Impulsive aggression doesn't happen out of nowhere," he says. "There's an interaction, let's say an argument between the aggressor and his boss. There's a stimulus to react and structures deep within the brain are pushing for the aggressor to do something."
Up till now, says Cocarro, everything is perfectly normal. But then differences start to emerge. In so-called normal people, another area of the brain, the lobes of the pre-frontal cortex, takes over. The pre-frontal lobes are situated just behind the forehead, over the eyes. Here is where Cocarro believes serotonin acts to moderate anger.
In most people, explains Cocarro, this inhibition is occurring before they are even aware of it. But for impulsively aggressive people, the frontal lobes exert less control over their anger. Once provoked, they almost immediately blow a fuse.
This condition probably affects at least one in 50 of the population, possibly more, says Cocarro. Some inherit the condition but environment can play an even greater role.
"The immediate environment where you grew up can have an influence, as a child or adolescent being the victim of aggression or violence as a kid, either by getting beaten up or being subject to corporal punishment, or even witnessing serious aggression," he said. Such traumatic experiences can lead to the brain producing less serotonin, possibly as a primitive defensive coping mechanism, suggests US research.
"If someone sees their father behave in an aggressive way, they are far more likely to behave in an aggressive way themselves when they grow up," says Dinan, now professor of psychopharmacy at University College Cork.
"There is a tendency for aggression to go from one generation to another as a way of coping with problems."
However, Dinan remains unconvinced that serotonin alone is the key to this condition.
"All we can say about serotonin at present is that yes, people who are aggressive appear to display different serotonergic functions to healthy individuals but you might also have hundreds of other different brain chemicals at work, and there are so many social aspects to aggressive behaviour to be considered."