What's going wrong in your brain when you can't shake traumatic memories

Study in mice bolsters theories of fear regulation

A new study published in the journal Science Advances has identified a brain circuit that helps regulate fear resulting from psychological traumas and could potentially lead to more advanced treatment for certain anxiety disorders.

Humans and other animals naturally begin to fear stimulus perceived by our brains as startling or potentially harmful. Luckily, the brain has an ability determine when such stimuli are in fact "harmless or resolved," Bret Stetka writes in Scientific American.

Previous research has identified the relationship between the amygdala (which is involved in emotional reactions) and the prefrontal cortex (which helps with decision-making) as key to this process. Often, those areas are damaged in people with post-traumatic stress disorder (PTSD). However, the precise relationship between the two regions of the brain and their connected role in preventing recurring traumatic memories has not been clearly understood.

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Study findings

To better understand how the brain regulates fear, a research team led by Andrew Holmes of NIH manipulated the brains of mice using a virus that caused their cells to turn off or on based on scientists shining light of a certain color at the rodents.

The researchers then conditioned the mice to fear a certain sound by administering an electric shock every time it was played. Normally, mice that later repeatedly hear that same sound without being shocked will lose their fear of the tone. But when the researchers disrupted the ventromedial prefrontal cortex-amygdala pathway, they found the mice did not unlearn their fear of the tone.

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They also found stimulating the connection enhanced the ability of mice to extinguish their fearful memory of the tone.  

Implications

Holmes says isolating the brain connection that helps regulate fear could help to improve the treatment of PTSD, and the researchers say the findings could have implications for combating other anxiety disorders, too.

"To regulate fear extinction," Holmes says, "I think it will be better to isolate and fix that one line of communication as opposed to trying to reengineer the hubs themselves" (Stetka, Scientific American/Salon, 8/6; Lewis, Business Insider, 7/31).


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