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Fear short circuits the brain, especially when it hits close to home, experts say— making coping with events like the bombings at the Boston Marathon especially tricky.

“When people are terrorized, the smartest parts of our brain tend to shut down,” says Dr. Bruce Perry, Senior Fellow of the ChildTrauma Academy. (Disclosure: he and I have written books together).

When the brain is under severe threat, it immediately changes the way it processes information, and starts to prioritize rapid responses. “The normal long pathways through the orbitofrontal cortex, where people evaluate situations in a logical and conscious fashion and [consider] the risks and benefits of different behaviors— that gets short circuited,” says Dr. Eric Hollander, professor of psychiatry at Montefiore/Albert Einstein School of Medicine in New York. Instead, he says, “You have sensory input right through the sensory [regions] and into the amygdala or limbic system.”

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This dramatically alters how we think, since the limbic system is deeply engaged with modulating our emotions. “The neural networks in the brain that are involved in rational, abstract cognition— essentially, the systems that mediate our most humane and creative thoughts— are very sensitive to emotional states, especially fear,” says Perry. So when people are terrorized, “Problem solving becomes more categorical, concrete and emotional [and] we become more vulnerable to reactive and short-sighted solutions,” he says.

Every loud sound suddenly becomes a potential threat, for example, and even mundane circumstances such as a person who avoids eye contact can take on suspicious and ominous meaning and elicit an extreme, alert-ready response. Such informational triage can be essential to surviving traumatic experience, of course. “Severe threats to well-being activate hard wired circuits in the brain and produce responses that help us survive,” explains Joseph LeDoux, professor of psychology and neuroscience at New York University, “This process is the most important thing for the organism at the moment, and brain resources are monopolized to achieve the goal of coping with the threat.”

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Says Hollander, “To some extent, that type of behavior is good because if you’re in a forest and get attacked by a snake or a lion, you want to be able to react quickly without too much thinking.” Indeed, our ancestors who spent time contemplating whether or not a risk was real more often that not would not have lived to rationalize their way through such situations again.

But once the immediate threat has passed, this style of thinking can become a hindrance, not a help. “The problem is that often people have these intense reactions and are not able to think about the situation or concept more realistically,” Hollander says. The fear can become generalized so that ordinary experiences like being in a crowd or seeing a backpack trigger intense anxiety.

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Traumatic events typically evoke a whole suite of brain responses, such as making people faster to startle, increasing their reaction time and producing hypervigilance to any type of sensation that might be linked with the threatening experience.

And this warping of perspective is exactly what terrorists aim to achieve. “Terrorists are trying to induce fear and panic,” says Hollander, noting that media coverage that repeats the sounds and images of the events maximizes their impact. The coverage keeps the threat alive and real in people’s minds, and sustains the threat response, despite the fact that the immediate danger has passed. The marathon attacks were particularly damaging, he says, because “All of sudden, there’s trauma associated with what had been a meaningful, communal event.”

It doesn’t help that the most common coping mechanisms can make matters worse. People who live in fear tend to want to sleep, drink alcohol or turn to sedatives to ease their anxiety. But, says Hollander, “It turns out that you are better off staying up than trying to go to sleep.” Sleep tends to consolidate and lay down traumatic memories. And that’s partly why the Israeli army, for example, tries to keep traumatized soldiers awake immediately after a difficult experience and engage them in warm social contact, both of which help reduce the risk of post-traumatic stress disorder (PTSD).

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Fortunately, our brains are designed to modulate fear responses and at least 80% of people exposed to a severe traumatic event will not develop PTSD. Studies show that the more support, altruism and connection people share, the lower the risk for the disorder and the easier the recovery. Because such interactions aren’t always easy in the immediate aftermath of a harrowing experience, Hollander is investigating whether medications based on oxytocin— a hormone linked with love and parent/child bonding— might help to ease this connection.

If fear short circuits the brain’s normally logical and reasoned thinking, social support may be important in rerouting those networks back to their normal state. Which is why the selflessness and altruism we see in the wake of terror attacks is often the key to helping us to process and overcome the shock of living through them.