Today the most effective PTSD treatments are cognitive behavior therapies, also known as exposure therapies.
In such treatments, patients are encouraged to confront their traumatic memories, and therapists help them overcome the associated anxieties.
Richard McNally, a PTSD expert at Harvard University in Cambridge, Massachusetts, compared exposure therapy to watching a scary movie again and again so that over time the movie no longer seems frightening.
However, he said, some people are reluctant to participate in such therapy because they find it too distressing. Others "may enroll in therapy but not participate fully for the same reason and may therefore not benefit," he added.
LeDoux, the NYU researcher, said the idea of using beta-blockers to treat PTSD is based on a recent finding that recalled memories are vulnerable to interference, LeDoux said.
"When you retrieve a memory, you're not retrieving a carbon copy of the experience but some concept of what you think actually happened. And you have to reconstruct that in your mind as a memory," he said.
The reconstruction is based not only on the event but also on things the brain has learned and stored in the meantime. When the memory is re-stored, the new experiences are re-stored with it.
LeDoux and his colleagues believe that propranolol can interfere with this re-storage process.
The drug blocks the effect of stress hormones on the body, relaxing blood vessels and calming nerves. It is effective in curbing high blood pressure and is also used to aid people in stressful situations like public speaking, McNally said.
McNally's Harvard colleague Roger Pitman has shown that propranolol may prevent emotionally vivid memories from taking hold, if it's given to patients immediately after a traumatic event such as a car wreck or an assault.
Previous research conducted by James McGaugh, a psychologist at the University of California, Irvine, found that propranolol weakens the formation of stressful memories in rats exposed to traumatic experiences.
In a follow-up study, LeDoux and colleagues used an electric shock to condition rats to fear a tone. The researchers found that the rats lost their fear of the sound if they were given propranolol after the tone started. Following this finding, the researchers shifted their focus to humans.
Current trial participants are asked to take a dose of the beta-blocker when they feel the onset of PTSD symptoms. In theory "you'd only have to take it once if it works the way animal studies suggest," LeDoux said.
But because human memories are more complicated than those of rats, effective treatment will likely require repeated doses.
Paul McHugh, a mental health professor at Johns Hopkins University in Baltimore, Maryland, told Nature that treatment of PTSD with drugs like propranolol could be abusedfor example, to desensitize soldiers to the atrocities of war.
"If soldiers did something that ended up with children getting killed, do you want to give them beta-blockers so that they can do it again?" the journal quoted him as saying.
Rothbaum and McNally told National Geographic News that such fears of abuse are unfounded.
LeDoux acknowledged that the study raises "big ethical and moral issues" but said there is no indication that beta-blockers will erase memories.
"We're altering the emotional impact of the memory," he said.
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