People handle stress differently, but previous studies show these differences are not entirely genetic. What, then, determines how a person responds to stressful situations and predicts his or her susceptibility to mental illness? A recent study using a mouse model attempts to find the answer.
In the study, researchers looked at the electrical signals that pass between the brain regions responsible for fear and stress--the amygdala and the prefrontal cortex. The pattern of signals between the regions allowed researchers to predict the animal's response to stressors.
The prefrontal cortex is responsible for planning and higher-level functions. The amygdala is the fear center that is involved in the "fight-or-flight" response. Together, they communicate via electrical patterns that can be used to predict susceptibility to stress.
Kafui Dzirasa, assistant professor of psychiatry and behavioral sciences at Duke University Medical Center led a team of researchers to study the pathway to stress and mental illness. They implanted electrodes into the brains of mice to hear the electrical patterns of signaling between the two regions in question. What they heard helped them determine the strength of the connection, or cross talk, between the two.
When they exposed mice to stressors daily, they found that the extent to which the prefrontal cortex controlled the amygdala correlated with the animal's response to stress.
They then tested the response to initial stress, before the mice were placed in a stressful situation. The researchers found that the mice that exhibited greater sensitivity to chronically stressful situations showed higher activation of the electrical pathway between the prefrontal cortex and the amygdala, when compared to the less sensitive mice. In other words, even before entering a highly stressful situation, the brain has a particular "signature" of electrical patterns that makes it more or less sensitive to stress.
Using this signature could help prevent mental illness, if Dzirasa and colleagues can harness the findings into a treatment.
"In soldiers, we have this dramatic, major stress exposure, and in some individuals it's leading to major issues, such as problems sleeping or being around other people," said Dzirasa, who hopes that pairing the electrical signatures with a stress treatment may prevent symptoms of stress-related mental illness, such as PTSD.
The findings were published in Nature Communications.
The group will look next at the potential connection between the circuit's signature and any genetic variations that make a person susceptible to stress-related mental illness. Eventually, research may yield more clues to separate susceptibility to stress from resilience, and will one day help curb the onset of psychiatric disorders in an increasingly stressful world.
