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Hormones such as glucocorticoids are one way that chronic stress “gets under the skin,” according to the late Rockefeller University neuroscientist Bruce McEwen, who pioneered research in this area. When released under conditions of acute stress, glucocorticoids power fight or flight by shunting metabolic energy away from processes such as digestion and toward the heart, lungs, brain and muscles. These emergency reactions consume energy and cause wear and tear throughout the brain and body.

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Lisa Feldman Barrett, a professor of psychology at Northeastern University, argues that the brain is not necessarily trying to minimize cost—it’s simply trying to spend energy efficiently. States of uncertainty that cannot be resolved can be particularly inefficient. “In uncertainty, your brain has to assemble many plans and maintain those plans over a period of time,” she says. “And that’s just expensive because there’s more going on. There’s more signaling. There are more chemicals.” Symptoms such as a lack of motivation or pleasure and a feeling of being stuck can be “indicators of being strapped for energy,” Barrett says. When less energy is available to update predictions and you see the world as bleak, you may continue to have that view even when conditions are actually improving.

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Anxiety disorders may involve a different type of prediction problem that relates to reduced plasticity. Here you overgeneralize from one bad experience: if you get bitten by one dog, you might fear all dogs; if you fail one test, you may see yourself as a failure. “The more you avoid, the more you think your prediction was accurate,” says Philip Kendall, director of the Child and Adolescent Anxiety Disorders Clinic at Temple University. “‘I can’t go near that dog; it’s going to bite me.’ So [you] don’t go near the dog. [You] don’t get bitten. And you go, ‘See that—the dog would have bitten me, but I’m safe.’ That’s a false confirmation of a prediction, [and it] leads to more avoidance.”

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Still, the majority of people faced with traumatic experiences don’t develop psychiatric problems such as PTSD or depression. George Bonanno, a psychologist at Columbia University, explains that many people who have intense symptoms initially—such as nightmares and flashbacks—won’t develop PTSD. These symptoms may reflect the brain’s attempts to integrate and learn from what happened. “Your brain is trying to make sense of all that information,” Bonanno says. “This is one of these things that the public doesn’t hear about—that intrusive memories [or] even nightmares after something really disturbing or life-threatening are not uncommon, and they’re actually adaptive. But then, for some reason, that turns into PTSD in some people.”

Read the whole story (subscription may be required): Scientific American