When ISIS terrorists attacked Paris on Nov. 13, they took 130 lives and wounded hundreds more. But their bloody acts may have injured far more people -- both survivors and the countless numbers who experienced the event vicariously through horrific media images -- in an insidious way, by causing potentially harmful changes in their brains.
Indeed, terrorism's effect on the brain is so powerful that those who survive attacks have significantly higher rates of post-traumatic stress disorder than those who make it through accidents or natural disasters. But terrorism also is linked to long-term problems such as anxiety and alcohol abuse in people who only have secondhand exposure to the event by watching it on television.
Recent research shows fear of future terrorist attacks can alter brain chemistry in a way that increases your risk of dying eventually from a heart attack or other ailments that might seem unrelated to the violence.
The latter study, published in 2014 in Proceedings of the National Academy of Sciences, looked at more than 17,000 Israelis, who live in a country where terrorist attacks are a frequent occurrence.
The subjects who had the most fear of terrorism tended to have resting heart rates that were 10 to 20 beats per minute faster than the norm, an indicator of increased risk for heart attacks and strokes. The elevated heart rate was linked to a change in brain chemistry. Blood tests revealed a decline in the function of acetylcholine, a neurotransmitter involved in responses to stress and which acts as a brake to the inflammatory response.
"Our brain reacts to acute stress situations by a rapid burst of acetylcholine release," explained study co-author Hermona Soreq, a professor of molecular neuroscience at the Edmond and Lily Safra Center for Brain Sciences at Hebrew University in Jersusalem.
"The brain sends the acetylcholine to body tissues through the vagus nerve; Since acetylcholine blocks inflammation responses, too much of it weakens the immune system. We found lower prospects to survive in patients after heart attack whose blood tests show weakened capacity to destroy acetylcholine."
Soreq said that terrorism-induced anxiety also causes the production of small molecules called microRNAs, which block the function of numerous other genes, and can alter regulation of the nervous system.
Terrorism triggers mechanisms hard-wired into the nervous system by evolution, which enabled our ancient ancestors to escape from animal predators and rival human clans. The human brain and vision system is fine-tuned to spot things that we should be afraid of, and then react to them in a flash -- even without consciously realizing it.
In a 2012 study, for example, researchers from the University of Edinburgh and New York University trained subjects to fear certain pictures by giving them mild shocks. Some subjects were allowed to look directly at the images, while others only got to glimpse them in one eye while researchers flashed a colorful image in the other eye to interfere with conscious perception.
Even with that hindrance, the subjects who got the one-eyed glimpse actually developed a fear response more quickly.
When a person spots danger -- say, a gunman who bursts into a theater -- the alarm is sounded in the amygdala, a sort of biological alarm system that triggers the body's response. It directs glands to release an array of chemicals such as adrenalin and cortisol, which shift the heart, lungs and muscles into high gear. The senses shift into narrowly focused hyper-awareness of information that might aid in survival.