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Scientists Discover "Switch" That May Turn Off PTSD Fear Response

People with post-traumatic stress disorder (PTSD) suffer from fear and anxiety long after the traumatic events that triggered their PTSD.

We try to stop these debilitating feelings with a gamut of remedies, from counseling to medication, but what's the neural mechanism that sustains fear in people even when their environment is now safe?

A team of neurobiologists from the University of California San Diego (UC San Diego) researched the mysterious mechanism behind this response and found what they characterize as a switch in the brain that causes "fear generalization." In fact, they even uncovered a method that may stop fear in its tracks.

In a new study published in the journal Science, they detail how they came upon this mechanism by experimenting on lab mice, studying their brains, and comparing them to the brains of people who have suffered from PTSD.

First, they took a group of lab mice and subjected them to electric shock, which caused the creatures to overreact in different situations — a sign that they had acquired a generalized feeling of fear.

The scientists studied their brains and found that a neurotransmitter, or a chemical that allows neurons to communicate, switches to another type of neurotransmitter that allows for this "generalized fear" to persist after the stressful trigger is over.

The switch happens in the dorsal raphe, which is in the brainstem of the mouse brain, the scientists found. They found a similar situation in postmortem dissections of brains belonging to people who had known PTSD.

In order to stop this fear response in mice, the scientists injected them with a harmless virus meant to stop this neurotransmitter switch, which curtailed the mice's generalized fear reaction. In addition, they gave the mice Prozac right after they experienced a stressful situation. Both methods appeared to stop fear in its tracks.

The study suggests ways we can mitigate PTSD and other mental disorders in the future, the scientists write.

"Our results provide important insights into the mechanisms involved in fear generalization,” principal investigator and UC San Diego neurobiology professor Nicholas C. Spitzer said in a statement. "The benefit of understanding these processes at this level of molecular detail — what is going on and where it’s going on — allows an intervention that is specific to the mechanism that drives related disorders."

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