If you've ever been suddenly and unexpectedly reminded of a past trauma, you may wonder if those old fears will ever stop haunting you.
Now, neuroscientists say they've discovered a group of brain cells that controls frightening memories, and they suggest that the finding could lead to new ways to treat anxiety, phobias and post-traumatic stress disorder, or PTSD.
The newly identified "extinction neurons" suppress fearful memories when they're activated, or allow fearful memories to return unexpectedly when not activated, according to researchers at the University of Texas at Austin.
It's long been known that memories believed to have been buried can suddenly appear and trigger a form of relapse called "spontaneous recovery," the study authors explained in a university news release.
"There is frequently a relapse of the original fear, but we knew very little about the mechanisms," said study senior author Michael Drew, an associate professor of neuroscience.
"These kinds of studies can help us understand the potential cause of disorders, like anxiety and PTSD, and they can also help us understand potential treatments," he said in the news release.
Drew and his team discovered that brain cells that suppress fear memories are in the hippocampus. This was a surprise because fear is associated with another part of the brain, called the amygdala.
The hippocampus, responsible for memory and spatial navigation, appears to play a significant role in giving fear a context. For example, it may link a fearful memory to the place where it occurred.
The findings may help explain why exposure therapy, one of the leading ways to treat fear-based disorders, sometimes becomes ineffective.
This type of therapy is designed to create new, safe memories that can override an original fearful memory. For example, if someone is afraid of spiders, exposure therapy may involve letting a harmless spider crawl on the patient. The safe memories are called "extinction memories."
"Extinction does not erase the original fear memory but instead creates a new memory that inhibits or competes with the original fear," Drew said. "Our paper demonstrates that the hippocampus generates memory traces of both fear and extinction, and competition between these hippocampal traces determines whether fear is expressed or suppressed."
With these new findings, the frequency and timing of exposure therapy may need to be reconsidered, and new pathways for drug development explored, the study authors suggested.
The study was published April 1 in the journal Nature Neuroscience.
The American Psychological Association has more on exposure therapy.
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