What would drive a rational person to escalate a minor confrontation into a dangerous showdown between a car and bicycle?
Experts say that all it takes is a raised middle finger to trigger the brain's "rage system," which shuts down rational decision-making and activates the "fight or flight" response, sending adrenalin pulsing through the bloodstream and preparing limbs for battle.
When people experience normal anger, they feel frustrated, but can still weigh pros and cons and solve problems.
When they are enraged, they become irrational, lashing out at anyone around them, including those they love, said anger expert Ron Potter-Efron, who has authored half a dozen books on the subject, including one titled Rage. Many report feeling as though their bodies have been taken over. In extreme states, they may black out and forget what they did.
"It overpowers the brain and literally shuts down the sensory systems and the power of reason," said W. Doyle Gentry, author of Anger Management for Dummies and founding editor of the Journal of Behavioral Medicine. "You are literally out of your mind," he said.
People with a reputation for losing their tempers and those who are easily stressed and impulsive are most at risk, Dr. Gentry said.
Scientists cannot say precisely what is happening inside the brain to cause these changes. But Washington State University neuroscientist Jaak Panksepp has identified what he has called the "RAGE system," which centres on the amygdala, the emotion-centre of the brain.
What makes rage so dangerous, he said, is that this system works in a "see-saw balance" with the neocortex - the cognitive, rational decision-making part of the brain - so that, when the emotion-based rage system is triggered, the neocortex shuts down, creating a toxic potential for unchecked violence.
Drugs like alcohol, which limit inhibition, add poison to the brew, said University of Toronto Scarborough neuroscience professor Michael Inzlicht.
York University's David Wiesenthal is one of the country's leading experts on road rage. He said that being behind the wheel in this state can be especially deadly.
Normally, when people are faced with life-altering decisions, from marriage to how to treat a disease, they have time to step back and rationally consider their options, he said.
But on the road, in the heat of the moment, they don't have the time or cognitive ability to take into account potential consequences, from injuring themselves or others to winding up in jail.
"Someone's life can take a tremendous turn in a few moments," Dr. Wiesenthal said.
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When a person becomes enraged, the brain's higher level rational thinking functions, located in the prefrontal cortex, are suppressed. At the same time, the primitive parts of the brain that control emotion, including the amygdala, take over. At the very moment when our decisions may matter most, our ability to think rationally is diminished.
Once the brain's " rage system" is activated, it sends adrenalin and other stress hormones through the body, triggering the nervous system's " fight or flight" response.
Possible physical symptoms include:
Headaches and exhaustion often occur after an episode
Increased heart rate and cardiac output, constricted/ dilated blood vessels, increased blood flow to the muscles
Increased perspiration
Increased blood glucose concentration
Relaxed intestinal and bladder muscles
Increased air flow in and out of the lungs
Dilation of the pupils, tunnel vision
Tremors or shaking
Non-emergency body systems, such as digestion, are suppressed
TRISH McALASTER / THE GLOBE AND MAIL
SOURCE: BRITANNICA. COM