Researchers at the University of Colorado at Boulder believe they have an answer as to why some people can quickly bounce back from a terrible event, while some seem to never recover.
They discovered that an area in the brain called the ventral medial prefrontal cortex computes whether or not stress-inducing events are under behavioral control, and if they are, it sends an "all clear" message.
"If you feel that you have control, it sends a message to the brain stem to cool it, bad things are happening but you don't need to get so excited," said Distinguished Professor Steven Maier of the CU-Boulder psychology department, who led the study.
The discovery could lead to better understanding and treatment of disorders like post-traumatic stress disorder and depression.
Maier presented the results of the study during the American Psychological Association's annual meeting this month in Washington, D.C.
The fact that everybody reacts differently to stress partly has to do with what is called variable behavior control, according to Maier. Prior to this study, it was generally believed that a lack of control caused the brain to spark up the body's stress-induced defenses like heightened awareness and anxiety.
"When something bad happens to you, your brain works to figure out whether you can control what is stressing you out or not," Maier said. "What we found is that it is the belief that you have control over something that allows you to not experience undue stress and other primitive reactions.
"So I would argue that those who bounce back from bad events quicker feel like they have control over the event. Perhaps they have a positive outlook while the others don't feel in control."
During their study, which involved rats, they determined that the ventral medial prefrontal cortex in the brain detects whether a stressor is under control, and if it is, the stress-induced activation of the brain stem is stopped.
"When you experience something bad, very primitive regions in the brain stem are activated, causing things like elevated stress that allow us to respond to whatever is bothering us," Maier said. "In primitive organisms the same thing happens when the brainstem is activated. However, as organisms evolved and became more complex they developed the ability to alter threatening events by behavioral means.
"Thus it is not surprising that more newly evolved regions of the brain, such as the medial prefrontal cortex, developed the means to inhibit activation of stress-responsive sites in the brainstem."
Regions in the brainstem that control stress levels are unlikely to be able to perform the complex computations necessary to process or detect whether or not a stressor is controllable. So they studied the prefrontal cortex and determined that it is the place making the determination, Maier said.
When you experience a dire emergency, all of these systems in the brainstem are activated and function to start a fight-or-flight reaction, he said.
Now that they know that a small part of the prefrontal cortex keeps the brainstem in check, they can work to understand how problems with this control mechanism develop.
"The problem is our own world has changed," Maier said. "The environment we live in changes much faster than the genome. When you get fired from your job, the same mechanisms are activated as in a fight-or-flight situation. This is a situation where it would be very beneficial to stop these functions, rather than allow the stress to continue until the body is worn down and you get sick or something worse happens."
He said the next step is figuring out how the process works.
"Once we understand in detail how the prefrontal cortex interacts with the brainstem in times of stress, then we can work on figuring out therapy or drug treatments," he said.