If the response in rats is any indication, re- ! searchers believe they have made a discovery that could eventually help people with anxiety and post-traumatic stress disorder (PTSD).

Like humans, rats learn to be scared of events or things that they relate to pain. But when researchers electrically stimulated a part of the brain, the rats "forgot" they were afraid, according to study coauthor Gregory Quirk, a professor of psychiatry at the University of Puerto Rico School of Medicine. "'We've fooled the brain into thinking that it's safe."

When faced with something frightening, rats will freeze and their heart rates and blood pressures go up—a classic fight-or-flight response, Quirk says. It's a hard-wired way that organisms deal with danger. That's true across many species—people, rats, birds and lizards, he adds.

In his study, Quirk taught rats to associate an audio tone with a mild shock to their feet. They froze each time they heard the tone. Then the researchers tried to make the rats forget about their fear by playing the tone without administering the shock. The rats lost their fear of the tone after it was played many times without a shock, but as soon as the tone was followed by a shock again—even after a lot of time had gone by—the fear and freezing response came right back, Quirk says.

The rats did a better job of forgetting their fear—and not reacting to the tone—when researchers electrically stimulated a part of the brain that's associated with learning that something is no longer scary.


The findings could help people who can't learn to stop being afraid, such as those who have PTSD, he says. "In the current therapies, you find what the person is afraid of, and keep showing it to them again and again to extinguish their fear. But with time, the fear response slowly recovers, and that's a problem," he explains.

The proposed brain stimulation may be too broad to be effective in humans, says James L. Olds, a neuroscientist and director of the Krasnow Institute for Advanced Study at George Mason University It would turn on too many nerve cells in an important part of the brain, he says. But the findings are still remarkable and provide much insight into how the brain works, he says.

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